R100GS PD charging light not lighting up.

[bubbles]

My 1991 GS appears to have a charging fault, it has Thunderchild diode board which has been fitted for probably 20 years, and I’m struggling to understand what the voltage regulator looks like. The Haynes wiring diagram shows the voltage regulator with 4 wires, 3 connections D+, D-,DF but I’m unable to find that on my bike. I have taken the instrument panel apart and checked the charging lamp and that’s ok. I understand the charging system on my 1978 80/7 and have changed the voltage regulator, alternator, rotor, stator and diode board on that in the past but I’m at a loss to know where to start on the GS, any help would be appreciated.

 

[Stirlingmoz]

The regulator is usually under the tank on the right side of the frame behind the headstock.

Once you’ve located it, a quick check you can do to determine if it is the voltage regulator or alternator system giving you problems is to remove the plug from the voltage regulator. Jump the blue and black wire and start the bike up. If the charge light goes out, you have an issue with the regulator. If the charge light stays on, the problem is likely in the alternator or diode board.

Alternator brushes are also worth checking

 

[bubbles]

The regulator is usually under the tank on the right side of the frame behind the headstock.

Once you’ve located it, a quick check you can do to determine if it is the voltage regulator or alternator system giving you problems is to remove the plug from the voltage regulator. Jump the blue and black wire and start the bike up. If the charge light goes out, you have an issue with the regulator. If the charge light stays on, the problem is likely in the alternator or diode board.

Alternator brushes are also worth checking

Yep that’s where it is on my 80/7 but can’t find anything that looks like the voltage regulator on the GS?

 

[mikeyboy]

I’m not familiar with the thunderchild rectifier,
Can you post a photo or two of it along with the wiring connectors?

 

[bubbles]

I’m not familiar with the thunderchild rectifier,
Can you post a photo or two of it along with the wiring connectors?

Thanks for your interest, will see what I can do tomorrow.