Headlight switch disconnect from stator

[Larry D]

My '81 GS 450S, wired properly with a new SH775, charges fine until I turn on the headlight, especially the high beam.
Will disconnecting the headlight switch from the "3rd"stator leg cure this ?
What effect does this procedure have on the charging system exactly ?
Keep it simple please, I'm an idiot on electrical.
Thanks.

[unfocused]

My issue with this swap based on my experiences after doing it. GS750 wiring harness - GS1000 engine

I had charging issues - would not charge above 12.9 volts and would drop to static battery voltage the longer it idled... with lights on, it was worse.
I only used x3 wires as I removed the headlight circuit from the stator prior to my swap.
All this does - when you turn the key on, the headlight doesn't come on until the bike is started. After removing these wires from the stator and wiring them up to your harness, your headlight comes on with the key switch instead. Motorcycle batteries back then were poor at best and the charging systems never got any better until they went to external charging systems.

First thing - all bulbs that have an LED replacement got one - helped a little.
2nd - I had to swap coils because of my swap to electronic ignition - helped a little more - this was a big issue with my setup and shouldn't apply to yours
3rd - new AGM battery - help a little more
4th - check, clean, repair all battery connections at BOTH ends of the cables. I run a couple of extra grounds.
5th - time to check the stator for any issues.

My charging system WITH the lights on ( i have an off/on switch and this switch turns all lighting off except for the brake light ) averages about 13.4 volts at idle - I'm ok wth this.
Charges 14.2 volts with lights off or when engine is above 2000 rpms aka when riding.

Also - make sure you fused the the V.R.

[Grimly]

My '81 GS 450S, wired properly with a new SH775, charges fine until I turn on the headlight, especially the high beam.
Will disconnecting the headlight switch from the "3rd"stator leg cure this ?
What effect does this procedure have on the charging system exactly ?
Keep it simple please, I'm an idiot on electrical.
Thanks.

I suspect there's a duff connection in the extra wiring that used to bring in the third phase when you put the headlight on. As a result, only two phases of the stator are trying to supply the load that needs three to run it.

Take the three stator wires directly to the SH775 and disregard the bypass wire that goes up to the headlight switch.

[Nessism]

Try this. Super simple...

SH775 Install by nessism, on Flickr

[Larry D]

I don't have alot of time until next week to go thru the wiring connections. I did test the positive terminal on the battery to the positive on the RR with DC selected. The result was 2.0 - 2.1

[Larry D]

....sorry.....
It was .20 - .21

[Nessism]

I don't have alot of time until next week to go thru the wiring connections. I did test the positive terminal on the battery to the positive on the RR with DC selected. The result was 2.0 - 2.1

That's no good. There is a lot of resistance in the circuit.

Edit: Larry updated while I was replying. .2V is good!

Edit2: Realize, that the voltage loss along the + wire between R/R and battery is not related to resistance and looses in the stator loop wires. That is totally different.

[Datsa Noydb]

My '81 GS 450S, wired properly with a new SH775, charges fine until I turn on the headlight, especially the high beam.
Will disconnecting the headlight switch from the "3rd"stator leg cure this ?
What effect does this procedure have on the charging system exactly ?
Keep it simple please, I'm an idiot on electrical.
Thanks.

The stator has three sections, or "phases". Two of them are connected directly to the R/R (your SH775), the wire for the third one takes a detour to a second set of contacts on the headlight switch. When you turn the light OFF, it opens a connenction from the battery to the light, but it also disconnects the third phase of the stator to prevent overcharging. If your bike does not have a headlight switch that actually turns off the lights, the detour wire is still there, but stops in the harness under the tank, then loops back to the R/R. All those connections can get dirty and create a LOT of resistance, which is why we say to bypass the "headlight loop" and wire all three stator wires directly to the R/R inputs.

With your SH775, you have a better regulating systeim that will not overcharge the battery, but will also give you better charging at lower engine speed operation (idle).

Is your lack of charging only at idle,or is it low at higher engine speeds, too? At idle, it's not unusual to have lower voltage, but if it's lower at riding speeds, you need to see why it's not working right.