GL1200 Electrical System - Connecting to the System

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:Egyptian: Connecting new/additional loads, or aftermarket replacement components to the GW electrical system.

Previous electrical threads:

Power Junction: viewtopic.php?f=12&t=12677
GL1200 Electrical System: viewtopic.php?f=12&t=12703
1985 GL1200 Rectifier Testing: viewtopic.php?f=24&t=12722

There is a lot of information and discussion regarding this subject. There are as many recommendations on how to do this as well, and I expect some interesting discussion may ensue. The information provided is not to influence or change how someone else manages and maintains their bike's electrical system., but is presented as my understanding of the topic, and how I will undertake any electrical system changes to my '85 LTD.

I must caveat the following with an admission that I too have not always adhered to a best practice regime. I do; however, continue to look for a better understanding of what I am working on and when I find what appears to be a better way ahead that is based on sound information and logic, I try to include this new information into what I do.

I have also had real life experience with some of what I write, and sometimes the added expense associated with my decision(s) could have been avoided.

I have been researching how the electrical system is designed and works on my '85 LTD. I have come to an understanding of the electrical system on my '85 LTD and expect this to be common with the other GW models.

There will be some exceptions such as the 1500/1800 that have external alternators. How these alternators are designed and compared to an automotive alternator, and how these are connected into the respective electrical systems is anther subject.

Back to the older GWs such as my bike.

First tenet that I use is that the electrical system on the GW is designed the same as that of a car, and that the GW is a car on two wheels with everything crammed into a very small space.

I have browsed, read, researched the internet, and various forums to gain an understanding of electrical system design and concepts with regards to the various design components. This was expanded to include the addition of new components/loads to the electrical system, and aftermarket replacement components.

There has been one key element that is common between the motorcycle and automotive industry. The key element that is common between the two industries is the use of a junction, sometimes called a power junction, that distributes the electrical system power to various components. This is to be expected because the motorcycle industry is based on the automotive industry for a lot of design aspects.

This junction is where the alternator output connects to the vehicles electrical system. It is where the alternator output current is distributed to the various loads. I mention current at this point because another tenet that I observe is that the electrical system voltage is maintained at 14.2 VDC by the regulator, even though it will fluctuate but return to 14.2 VDC, depending on the various loads being applied/removed from the electrical system.

Another reason for this is that alternators are expected to maintain this mean electrical system voltage of 14.2 VDC (give or take a point or two) regardless of amperage output size. Discussion regarding alternators never revolves around voltage, but around amperage rating.

Having mentioned the above, I have looked at a number of motorcycle and automotive schematics, and have found this common element, I will call it a power junction, where the alternator current output is sent to all the loads, to be consistent. There is generally two wiring branches, one to the ignition switch and one to the battery. In reviewing electrical system schematics, you will notice that all loads (there are a few exceptions – not many) are after the ignition switch, or controlled by the ignition switch. The only primary exception is the battery.

The battery is used to start the bike, load levelling – voltage spike absorption, and supplemental power should the charging system not produce sufficient power for the electrical system operation. The industry mean voltage of 14.2 VDC is considered the optimal voltage to operate the vehicle electrical system and keep the battery fully charged.

At start, a battery in good condition is discharged approximately 3% of state of charge. Once the vehicle is started, the battery is quickly charged back to a 100% state of charge. The mean electrical system mean voltage of 14.2 VDC is forced into the battery at a high current rate. The battery accepts the charge until it gets back to or close to 100% state of charge, after which it starts to resist the current flow (in actuality the battery starts to resist the influx of power as soon as it starts), reducing the charging rate (amperes) until it gets to a point that results in a trickle charge to the battery. At this stage there is very little current flow to the battery.

As mentioned before, all loads are after the ignition switch. There are no additional loads connected to the wire going from the power junction to the battery, good design and works well.

Here are a few schematics to illustrate what I have mentioned above.
1985 GW Starter System 1.jpg
GL1200 LTD Schematic

In the GL1200 LTD schematic, there are no additional loads on the battery, all loads are after the ignition switch. This schematic shows one exception to the no additional loads on the battery side of the electrical system; however, the electrical system was designed this way, and my premise presented in this article is still sound.

Alternator Change.JPG
Automotive Electrical System

In the automotive electrical system schematic, you will notice that a junction block, a power junction, is used to distribute the output from the alternator. It also shows that the sense wire to the regulator is joined at the junction block as well.

Automotive Electrical Schematic 2

In the above schematic, a junction block, power junction, is used to distribute the output from the alternator.

gl1200 charge system schematic.JPG
GL1200 Electrical Schematic

The GL1200 electrical schematic above also has a power junction where the alternator output is distributed to the electrical system.

In all the above schematics, there is a power junction to distribute the alternator output to the electrical system. Even though the battery is an essential element in the operation of the electrical system and bike operation, that when it comes to power distribution, the battery is considered only as a load on the system that we know requires varying degrees of current input. The automotive schematics provide a simplistic representation of the electrical system; however, the follow on schematic details regarding electrical loads would be after the ignition switch.

Enter the human factor. This is where the design intent of the OEM meets us, and then all bets are off.

As our bikes have aged, replacement parts from the OEM have been discontinued, and aftermarket components have been developed, we have had to adapt to the changing landscape. There have been technological improvements that have us upgrading various components for better performance and reliability.

I would like to discuss aftermarket components that are intended to be direct replacements for OEM components.

One of these is the replacement of the OEM shunt type regulators. These degrade over time, and do fail. This type of regulator is very inefficient, but technology has improved and surpassed this shunt type regulator. Enter the series type regulator that uses the latest technologies.

With these new series regulators being used to replace the original OEM shunt type regulators, there is generally a difference in the number of wires from the regulator to the electrical system. This in itself is not an issue; however, it becomes an issue when the aftermarket manufacturer/distributor recommends connecting its unit to the electrical system that is not the same as for the unit that is being replaced.

Manufacturer/distributor installation instructions should be such that you can install the new unit using the existing wiring from the unit being replaced. There may be some modification to the OEM wiring connection, but this should be explained in the installation instructions, complete with how to make the changes. Installation instructions that do not do this, but recommend installation by bypassing/circumventing the original system wiring design for ease of installation is not a best practice scenario.

I understand the reasoning/rationale that has been the impetus for certain practices to become a matter of rote over the years. I submit that even though this approach will work, it may not always be a best practice scenario.

Not adhering to the original design of the electrical system can be problematic, and the system operation may be impacted and not in the best sense. As the owner/operator, you will probably question the change from the previous installation, and may or may not get an answer that fits your specific situation.

Another area of interest regarding this issue is the external alternator modification to replace the internal engine alternator stator, commonly called the “Poorboy” conversion.

Again, with the alternator conversion there is a lot of information on how to install the various components, but very little on alternator selection and how to connect the alternator into the bike's electrical system.

I have installed the alternator modification on my '85 LTD. Before I hooked the alternator into the electrical system, I removed the old charging system wiring, including the power junction. With the power junction removed, I installed a new wire from the starter solenoid to the ignition switch and commenced installation of the wiring to connect the new alternator up to the bike's electrical system.

RR Red-White Wire Splice - 2.jpg
Power junction Removed

When I removed the original charging system wiring, I did not have the same understanding of the electrical system as I do now, or understood how this affected the electrical system operation.

The alternator I selected for this modification was a 3-wire alternator, rated at 55 amps. It fit the operation profile and was small enough in size to be successfully hidden behind the lower left fairing without any modification(s) to the fairing. It is readily available at the local auto wrecker and very reasonably priced. I have since replaced the alternator first used with one from a 1988 Pontiac Firefly 1.0 litre turbo.

I have covered the different alternators that can be used for this modification in another thread. Suffice it to say, I would recommend a 3 wire alternator instead of a one or two wire alternator. Your requirements may differ and as such your choice of an alternator as well.

I installed the alternator output wire directly to the battery with a 50 amp circuit breaker in line. I connected a 12 VDC switched wire for excitation, a lamp wire for visual indication as to whether the alternator was working and the sense wire directly from the battery.

The charging system never worked quite as well as when the OEM system was installed. I submit that if the stator had not failed, I would not have an external alternator installed.

The integral dash voltmeter always indicated an electrical system voltage of some 05. to 0.7 VDC less than actual at the battery. The electrical system never seemed to adjust to voltage fluctuations as well as it should have, especially when the rad fan would come on. The electrical system voltage would drop, but not recover as one would expect.

Fast forward a year and a half, and armed with new knowledge of the electrical system, I decided to rewire the electrical system to replace the power junction that I removed.

Wiring schematic - 1.jpg
Schematic for Rewire of '85 LTD

I used this schematic as the template for the install of the new power junction and associated wiring change(s).

I used a Blue Sea power bar and installed it where the OEM regulator used to be located. The connections at this power bar are:

1. Alternator output wire;
2. Alternator sense wire;
3. Wire to ignition switch;
4. Accessory fuse block power supply;
5. Battery Tender connection; and
6. Charging wire to battery.

After the rewire, trialled the new power junction installation. The results were very good, and mirrored the electrical system operation before I did the external alternator modification.

This new power junction gives me the flexibility of adding additional power bars (power junctions) if required, and expect the electrical system operation to operate as designed.

The in dash voltmeter indicated electrical system voltage that was the same as that seen at the battery with a voltmeter – 14.2 VDC. I have 2 sets of driving lights that can be switched on/off, as well as the rad fan. I switched on the driving lights and the system recovered as it should. The rad fan was turned on, and the system voltage dropped but recovered as well. The charging/electrical system is now operating as it should.

Had I not removed the old charging system wiring, I would have been able to connect the alternator output and sense wire to the red/white wire going to the power junction and starter solenoid. The original rectifier black wire would be used as the 12 VDC excitation, and the only other wiring would be the indicator lamp on the dash.

If you are using a one wire alternator, the alternator output wire connects to the red/white wire going to the power junction and starter solenoid.

If you use a two wire alternator, the alternator output wire connects to the red/white wire going to the power junction and starter solenoid, and the original regulator black wire is used as the 12 VDC excitation to the alternator.

The last section of this article will deal with adding new/additional electrical loads to the bike's electrical system.

The accepted practice by most is to use the battery as a load/connection centre. There are aftermarket products such as accessory fuse blocks that are designed to attach to the battery terminal(s) to provide expansion possibilities for you, the owner. It is also the sentiment of many that this is the best way ahead. I have mentioned above and in my other threads that this is not always a best practice scenario.

The schematics I have included in this article clearly illustrate that the OEM design considerations are such that connecting new/additional loads at the battery terminals is not a best practice scenario as there are none. In researching this issue, the automotive industry, specifically in the vintage and early model car restoration sites, recommends installing or expanding on power junctions for new electrical loads instead of using the battery as a connection/load centre.

Having mentioned this, I would recommend that to add new loads to your bike's electrical system be be undertaken such that the connection is on the upstream side of the power junction (ignition switch side). This can be accomplished by connecting a new wire splice at or near the power junction. You can also install a new power junction, with the associated rewire.

There are many ways to accomplish what you want to do, but I again submit, that installing new loads correctly, and from the correct location in the electrical system wiring, will ensure continued correct electrical system operation.

To summarize:

1. Our older GWs have a power junction that is a key element in the correct operation of the electrical system;
2. Aftermarket replacement unit(s) should be installed the same as the OEM unit(s) being replaced;
3. DIY modifications should be installed the same as the OEM units that it is replacing; and
4. Connecting new loads to the electrical system should be at the correct location in the electrical system wiring harness.

I trust you have had a good read. It is a long post. The opinions expressed herein are mine based on my research and real life experiences. As I mentioned previously, I am not trying to convert or change how you work on and/or maintain the electrical system on your bike, but to present information as I have come to understand it.


dan filipi

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I believe some if not all of the voltage drop you were seeing when comparing battery and bike meter voltage has to do with voltage drop through the stock wiring. I could be wrong of course, but that was the case on my '83.
The reason this would be so is the stock "junction" point is closer to the loads being served, I.E the volt meter, and by moving the alternator feed wire (further) away from that point, to the battery instead, voltage drop through the additional smallish wire can be seen. Especially so when introducing additional load to that stock OEM main feed wire like the cooling fan.
The OEM alternator junction point is more at the center point of the loads in relation to distance from the battery.

Voltage and current, and the effect one has on the other by increasing or decreasing either is rather interesting.
If you increase the voltage, the current draw (watts) of any given load will drop. If current (load) increases, voltage will drop if voltage is not increased to compensate for the additional load.

Wire length and gauge have a profound affect on both. I often have to do voltage drop calculations at work. Sometimes if it's too cost prohibitive to increase the wire size, one solution is to change the taps on the transformer in 5% increments to compensate.
On the bike and car alternators, the alternator is designed to maintain a constant voltage output. The voltage is what the regulator maintains, the current draw follows. The alternator does not monitor current draw. It simply maintains the voltage at a set point all the way to it's maximum output capacity.

On my 1100 I installed a relay to power the fuse panel. I did this to remove the high current load from going through the ignition switch because I'd read numerous posts about ignition switches overheating and I wanted to avoid this.
The first benefit I saw was brighter lights. I then replaced the glass fuse panel with a new blade type panel.
After this, voltage reads on various wires on the bike and in the fairing were .1 volts +- to the battery voltage. This was true running or not, and whether running my external alternator or the stock internal alternator.

Your 1200 is loaded with a lot more stuff than mine so I think that these affects could be even more pronounced, but I'm glad you did the research and came up with a very good solution.


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This has all been a very good overview of the basic electrical/charging system. Much appreciated and should be tagged for reference.

But it also bears mentioning (and I haven't heard a whisper) that instrument calibration is critical toward confidence in any reading. The 7V regulator in the old wing that feeds the gauges is a notorious weak point. Not only is it prone to failure (most commonly reported), there is considerable drift in the measurement as the reference changes. So, in addition to the voltage drop and base reference point Dan mentions, the calibration is often jacked. That's yet another reason the factory gauges rarely agree with a DMM comparison.


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Dan/Desertrefugee - thanks for the comments. Agree with all your points. Don't be surprised if you find your thoughts/points are plagiarized in another post of mine as I expand on this issue. Having information consolidated in one location is a good thing I think, besides winter is coming, and a budding novelist such as myself needs to keep busy in retirement.

I have read and know that voltage drop is an issue with older wiring in vehicles. I have read about this in the various forums and have been thinking about changes I can do to improve the electrical system operation on my bike such as reducing the electrical load through the ignition switch much like what you have done Dan. I know of two power feeds into the fuse block on my bike. Will investigate this as it would just be another power feed from my new "power junction". Also have to find real estate to fit additional items such as relays - like these little items.

Interesting about the dash voltmeter. The increase in wire length was maybe 24 inches. I used an 8 gauge wire from the alternator to battery through a 50 amp circuit breaker - new marine grade wire. The wire size to the ignition switch is 12 GA - new marine grade wire, but after the ignition switch a myriad of smaller wires with lots of branches and the voltage reading was low by 0.5 to 0.7 VDC by the in dash gauge..

Fast forward to the rewire, and the alternator 8 GA wire is shorter by about 24 inches, the ignition switch wire is still 12 GA, but shorter by about 24 inches. There are multiple taps at the new "power junction". The web of wiring after the ignition switch is still the same. In dash voltmeter now reading within 0.1 VDC of battery reading using a voltmeter.

Lot of voltage drop for new wire and short lengths. Electrical was not my strong suit in my previous life. Regardless, like the new arrangement and dash voltmeter reading.

Agree with the instrument calibration. I have mentioned in previous posts on this (I think) and other forums that the installed meters should be used to demonstrate consistency in a system performance. It's when this changes that you should take notice, monitor and investigate if necessary.

Again, thanks for the comments. Always learn from these, and sometimes get idea(s) for small projects, and additional posts relevant to this subject line. Like doing the research as well.



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My previous post was done at 0300, and there are only so many brain cells firing at that time.

Connecting an external alternator or a series regulator (excellent upgrade to be considered) in place of the OEM rectifier has been well documented in various post/threads. In this thread I mention about connecting both these units to the OEM wiring harness instead of bypassing and going directly to the battery.

I had done this when I first installed the external alternator mod and I have mentioned how the electrical system was not responding as I would have expected. Having done a rewire and put the "power junction" back in, the electrical system is working as it should. Out for a ride this morning, a crisp 1 deg C, bike system, both sets of driving lights on and my heated gear hooked in - liner and gloves (heated gear needs approximately 8 amps when in use), on the highway the dash voltmeter indicated a steady 14.1 VDC. Doesn't get any better.

Regarding the upgrade to a series regulator, Joebarteam on another thread was having issues with charging and such and installed the Roadster Cycle series regulator IAW the install instructions. Improved system performance, but the volt meter readings were still less than actual. Recommended to connect the regulator up to the original wiring and the voltmeter readings reflected actual alternator output.

These are two examples where connecting the replacement units to the original wiring has been beneficial. This as tweaked my interest in that I will peruse the forums and look at the results of the various changes, how the change(s) were done. Be an interesting research project.

I'm definitely going to look into the power to the main fuse block relay mod as well.



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what's about this? have you already made a thread for it?

I'm definitely going to look into the power to the main fuse block relay mod as well.