Bad Key Switch on 71 XS1B?

[Jerm]

Non Charging issue on XS1B. Specifics inside.

I have a 2 Volt drop from battery to the brown wire coming out of key switch with the key on. I have full battery voltage all the way to the red wire entering the key switch.

Charging guide points to a bad key switch.

Are they serviceable? I opened it up and cleaned all the round contacts inside that hook to the wires and the piece that rotates back and forth to make the connection. It seems pretty straightforward. Seems like it would either work or not, not just rob 2 of the 12.5 volts. Thoughts?

 

[gggGary]

Yeah I've rebuilt several. early and late, did a 73 a month ago that was causing an intermittent headlight. cleaned polished, make sure that the spring in the rotating nylon part is creating some tension on the contacts. Maybe I got lucky, but this switch is working great now.

 

[Jerm]

Sounds good. I'll do it again.

 

[Jerm]

Tried it four times only to get the same result. Maddening to say the least. Next stop is a want ad in the classifieds. Thanks for the info!

 

[TwoManyXS1Bs]

Try resoldering the contacts...

 

[Jerm]

Its not the key switch. I swapped a new one on and got the same results. Also tested rotor, stator, and regulator. Here is what I have.

12.2 V at battery, engine off. 12.2 V on red wire entering key switch, key off. 10.7 V at Brown wire exiting key switch and brush with key on.

11.7 V at battery with bike idling. Apply throttle and voltage does not increase above 12 V at battery.

Rotor: 5.5 Ohms

Regulator unplugged and jumper from Positive Battery to Green Brush: Battery 12.2 not running. Drops to 11.6-12 running at idle, but does not climb on its own. Blipped throttle and it shot up to 15.

Stator:
Probing White wires at idle: 6.4 - 6.6 AC
Disconnect and Ohm check between whites on stator plug: .4 ohms

I also swapped another Stator onto the bike and got the same results.

Bad Regulator?

 

[TwoManyXS1Bs]

...12.2 V at battery, engine off. 12.2 V on red wire entering key switch, key off. 10.7 V at Brown wire exiting key switch and brush with key on.

That's a 1.5v drop, a bit much. If both ignition points are open, draw should be around 3 amps. If one of the points is closed, draw would be upwards around 6 amps. Of course, that would be with headlight off.

Same test on mine, I get 0.3v drop. In theory, that's also too much, so I'm going thru mine as well.

There's a major connector, battery/fuse line to harness (double red wires) between the backbone and battery box to clean. The brown, from headlight bucket back to regulator, has connection branches in the harness, like where it emerges at the coils, that could be failing. Member Angus67 chased some of that in his '71 XS1B thread(s).

... Regulator unplugged and jumper from Positive Battery to Green Brush: Battery 12.2 not running. Drops to 11.6-12 running at idle, but does not climb on its own. Blipped throttle and it shot up to 15.

That tells me that the rotor, stator, and rectifier are working. Also sounds like a poor battery that's drawing too much current during charge, keeping voltages a bit low.

... Bad Regulator?

Yep, that's what's left. The possible hi-current draw of the battery might have helped burn the contacts in the regulator. Cleaning/servicing the regulator can be done. Check its simple internal connections. Here's a schematic:

View attachment 57035


Also, include the observed voltages of the green brush wire in your tests...

 

[TwoManyXS1Bs]

Here's a couple of views of the backside of the regulator, showing the wiring to the main resistor.
Check, or even resolder, those terminations.

 

[Jerm]

Picked up another regulator and that cured the non charge issue. I still have to figure out the voltage drop. I installed a new AGM battery and repro wiring harness from mikesxs when I put it back together last month. Is there something in the LH bar switch that could be causing the voltage drop on the Brown wire coming out of the key switch when it is in the on position? Headlight is off. Turn signals are off. Only thing left is my Horn which does not currently work. Done probing wires for the weekend. I'll be back at it Monday.

 

[TwoManyXS1Bs]

Picked up another regulator and that cured the non charge issue. I still have to figure out the voltage drop. I installed a new AGM battery and repro wiring harness from mikesxs when I put it back together last month...

Great! That eliminates at least 2 gremlins.

Is there something in the LH bar switch that could be causing the voltage drop on the Brown wire coming out of the key switch when it is in the on position? Headlight is off. Turn signals are off. Only thing left is my Horn which does not currently work...

The horn is fed 12v by the brown, and its other side pink wire goes to the horn button, and grounds there. The headlight switch is fed by the red/yellow, so no brown there.

However, the flasher relay is an active internally-timed unit, and will draw a little bit. In a very quiet room, you can just barely hear it 'click' energize, under the battery box, when you switch ignition on. Maybe that's your mystery current draw?