Magneto/wiring help please

[Larry710]

1977 GT500

I am nearing the final stages of my build. I bought this bike last summer when it was stripped down to the crank, so every step has been a experience, and it continues....

The wire harness, and most lights were in bad shape. I had purchased and installed a plug and play lighting kit on a dirt bike in the past to make it street legal, and got the idea to do the same with this build. This one --> https://www.rockymountainatvmc.com/p/11 ... ghting-Kit" onclick="window.open(this.href);return false;
It has EVERYTHING need minus the headlight, which I had purchased a smaller 6" round one earlier.
So I stripped everything to do with the lighting away from the ignition; ignition switch and gauges,(i'm going to use a speedometer app on my phone). This is a cafe racer style build, minimal and clean!
Since there is no starter, the small 12v battery that comes in the kit will be easy to hide.

I replaced both charging coils, since they both had broken wires. Used new OEM suzuki parts. After getting the engine together and installed in the frame, the engine started on the second kick! the bike runs very well in the garage but still unable to test ride it, obviously.

I was trying to incorporate the lighting kit wiring harness into the magneto to charge the battery, and power the headlight. I put my multi-meter on the red wire from the regulator, to meter the voltage going to battery. I could only get 2.5v at best. This is where my troubles begin.

Why would I only get 2.5v? I just noticed tonight in the parts manual I have that the two charging coils are different part numbers, I forgot that when I installed them, could I have mixed them up and put in the wrong locations on the stator assembly? (Note, I did not remove the primary coils.) If I switch their locations, and wiring, would that cure my problem?

The R/G wire that comes from the regulator (and stator), and the G/W that comes from the stator, shows on my wiring diagram it goes to the "lighting switch" I assume this would be on the left handle bar control switch? I do not have the OEM. I can not read and voltage from either one, would this be AC voltage? do they need to be connected?

Summer time has arrived and I want to ride
Thanks in advance.

[tz375]

I am no expert on GT500 wiring but it should have PEI - magneto ignition. The rest of the charge coils connect to the charging system.

Red at the regulator comes from the rectifier and that gets its power from the battery, so that should read 13v or thereabouts without any charging going on. Do you have a wiring diagram? You need to get one and work from there.

Start by checking the battery and follow the red from battery to rectifier and to main (keyed) switch and from there it emerges as Orange to the lights etc. The red also goes from rectifier to regulator to alternator.

At rest with everything off, you should have full battery power on any Red line. Disconnect one at a time to see where the p[ower is getting lost, but start at the battery - is it fully charged?

Stock, one of the charge circuits from the alternator is wired via the headland switch (left bar) so that when the lights are on, that circuit is engaged and charges at a higher rate. If you run with lights on all the time, that can be connected directly to the rectifier.

You could also disconnect the charge coils and check their resistance to see how they compare to what the Workshop manual says they should be.

Next after that is to test and repair or replace the regulator. If it were my bike I'd see if Sparckmoto.com has a suitable unit and replace them both with new solid state devices. Ask Matt if he has one that will work on your bike.

[jabcb]

The GT500 wiring diagram is here: viewtopic.php?f=29&t=4743&start=15

Some dirt bikes have lights that operate on AC. We have no idea how your lighting kit is designed so its hard to provide advice.
Is there a wiring diagram for you lighting kit?

Stock, the GT500 uses a lighting coil to match the alternator output to the load. Only one charging coil provides power when the lights are off. Both charging coils provide power when the lights are on. That is why the G/W wire goes to the lighting switch.

Are you using the stock left-hand handlebar switches?
Are you using a modern rectifier/regulator?

[Larry710]

Thanks for the feed back.

Yes that is the exact wire diagram I am working with, but all lights and corresponding wiring is removed. I am left with one red to/from battery, and R/G & G/W to the lighting switch.

I do not have the original left handed switch at the handle bar, it wasn't with the bike when I bought it. however the new kit comes with one.

new kit is plug and play, simply connect new harness to battery, and the oem headlight wire to the new left hand bar switch.
what I am understand, I need to connect the R/G & G/W wires together, this in turn provides charging for the battery (red wire) and power for the headlight( orange wire, which I do not have)?

I can provide more info later today, currenty at work and don;t have much time.

thanks again

[tz375]

When you say that the wiring has all been removed, do you mean ALL as in the alternator to rectifier and regulator as well? Stock switches connect in that second lighting coil when the lights are on and it should be possible to wire both coils in to charge at all times.

The Kit is just a set of indicators plus relay and horn and rear light. As long as you have the stock ignition and charging circuits, wiring the rest shouldn't be too hard.

But step back for a moment. Leave the kit unconnected. You should have >12v at the red wire from the regulator/rectifier if your battery is not dead. First you need to determine what is going on between the battery and R/R. Without the bike running you should have more than 12 volts on red. Is the battery flat?

[Larry710]

The GT500 wiring diagram is here: viewtopic.php?f=29&t=4743&start=15

Some dirt bikes have lights that operate on AC. We have no idea how your lighting kit is designed so its hard to provide advice.
Is there a wiring diagram for you lighting kit?


Stock, the GT500 uses a lighting coil to match the alternator output to the load. Only one charging coil provides power when the lights are off. Both charging coils provide power when the lights are on. That is why the G/W wire goes to the lighting switch.Does the G/W connect to the R/G to activate both charging coils?

Are you using the stock left-hand handlebar switches?I do not have it, wasn't included with the bike when I bought it

Are you using a modern rectifier/regulator?

No, using all oem rectifier and regulator, I guess I need to learn how to verify they work.

[Larry710]

When you say that the wiring has all been removed, do you mean ALL as in the alternator to rectifier and regulator as well? Stock switches connect in that second lighting coil when the lights are on and it should be possible to wire both coils in to charge at all times. All lights, and associated wiring has been removed. Rectifier and regulator is still being used.

The Kit is just a set of indicators plus relay and horn and rear light. As long as you have the stock ignition and charging circuits, wiring the rest shouldn't be too hard. Yes, that is what I was assuming as well, however I need to determine the charging circuits are functioning

But step back for a moment. Leave the kit unconnected. You should have >12v at the red wire from the regulator/rectifier if your battery is not dead. First you need to determine what is going on between the battery and R/R. Without the bike running you should have more than 12 volts on red. Is the battery flat? I have 12.2v everywhere on the red wire when the engine is not running. BUT.... I did just notice tonight, that when the engine is running and I hold my meter on a red wire it first reads 12.2v then after a few seconds gets erratic, briefly jumping from 12v-13v-6v-0v! Something not right!

[Larry710]

To add to all the comments I made above in red text...

I put my meter on the R/G and G/W when the engine was running and there was nothing. I connected them and checked again, nothing.
I switch the meter to AC and nothing on the R/G, but 30v on the G/W!!! I checked the Y/G from the stater to rectifier and noting.
I would expect AC voltage from all 3 wires from the stater Y/G, R/G, and G/W?

Also, Rectifier is very warm/hot when engine is running. almost to the point where I can not touch it. I don't recall previous bikes I've had that got that hot.


I am second guessing myself with the earlier install of the two charging coils. they have separate part numbers
32131-15320 Coil, charging A
32132-15320 Coil, Charging B

Coil A is shown in the 8:00 position on the drawing, and B is at the 4:00. If I mixed them up and switched the locations, would that be causing my issues?

[tz375]

The alternator generates alternating current, so you have to check them - prior to the rectifier - on the AC setting. If one coil is not generating anything, check to see if it open circuit or shorted out.

You should get ac volts on all three legs if I read the wiring diagram correctly. Wait for jabcb to confirm.

Disconnect them and check resistance. One may have lost its ground or may be faulty. Both G/W to Y/G and R/G to Y/G should be around 1 ohm.

The factory workshop manual has details of testing procedures for the full bridge rectifier.

Regulator and rectifier tend to get hot, but it sounds like you have a dud rectifier. I would buy a new modern one from Sparkmoto or other supplier. With R/R correctly connected the battery voltage should rise to something around 14.5volts at 3,000 rpm.

[jabcb]

As tz375 suggested, with the alternator disconnected:
1) check resistance between Y/G & G/W, should be around 1 ohm
2) check resistance between Y/G & R/G, should be around 1 ohm
3) check resistance between Y/G & ground, should be open circuit

If you check AC voltage with alternator disconnected & motor running:
1) AC voltage between Y/G & G/W, should be over 15V (increases with rpm)
2) AC voltage between Y/G & R/G, should be over 15V (increases with rpm)

I recommend that you upgrade to a modern rectifier/regulator.
This topic shows wiring diagrams for the upgrade on a GT500: viewtopic.php?f=29&t=5963&hilit=gt500+r ... r&start=30
Since you don’t have the stock left handlebar switches, use the 3rd diagram.

I’ve had good luck with Tympanium rectifier/regulators.
https://www.ebay.com/sch/i.html?_from=R ... h&_sacat=0

[Larry710]

Been pretty busy, finally got time to put the 500 back on the work bench!

As tz375 suggested, with the alternator disconnected:
1) check resistance between Y/G & G/W, should be around 1 ohm I get 2ohm
2) check resistance between Y/G & R/G, should be around 1 ohm2 ohm again
3) check resistance between Y/G & ground, should be open circuityes

If you check AC voltage with alternator disconnected & motor running:
1) AC voltage between Y/G & G/W, should be over 15V (increases with rpm)
2) AC voltage between Y/G & R/G, should be over 15V (increases with rpm)Sorry for a stupid question, but with checking these, I'll be in AC setting of course, positive lead on the YG and negative on the GW? Same for YG-RG?

I recommend that you upgrade to a modern rectifier/regulator. Got a modern one ordered
This topic shows wiring diagrams for the upgrade on a GT500: viewtopic.php?f=29&t=5963&hilit=gt500+r ... r&start=30
Since you don’t have the stock left handlebar switches, use the 3rd diagram.

I’ve had good luck with Tympanium rectifier/regulators.
https://www.ebay.com/sch/i.html?_from=R ... h&_sacat=0

[Larry710]

Remember, I replaced both A and B charging coils.

But I am second guessing if I put them in the right locations. Looking at the parts manual, they have separate part numbers!

[jabcb]

Its AC, so it doesn’t matter which multimeter lead is connected which wire.

Originally one charging coil was for daytime use & the other was for powering the lights. So how you hooked them up might make a difference.

You will be wiring up the charging coils to be on all the time, so it doesn’t make a difference.
The coils are in phase. So two wires (one from each coil) connect to one rectifier wire & the other two connect to the other rectifier wire. You have to correctly match up the two charging coil wire pairs.

[Larry710]

If you check AC voltage with alternator disconnected & motor running:
1) AC voltage between Y/G & G/W, should be over 15V (increases with rpm)
2) AC voltage between Y/G & R/G, should be over 15V (increases with rpm)

Yes I get 20-30volts on both at idle! That is reassuring

I'll sit tight for my rectifier/regulator to arrive.

Thanks for all your help

[Larry710]

I thought it would be pretty straight forward

This is all the wiring diagram I have for the ebay purchased rectifier/regulator. How would you connect to it? What should I expect?