Electrical problems - voltage drop

[Nipedley]

Hey guys

Wondering if you can help me out here, having electrical problems with my 1990 GS500e:

Battery: 12.9v (just charged, 2 years old, charger tested the battery good)
Battery to reg/rec (permanent live): 12.9v
Battery to starter relay (permanent live): 12.9v
Battery to ignition switch: 12.7v

Now here's the problem, I turn the switch and:
Battery to ignition switch: drops to 0.5v
Switched live (to the rest of the bike from ignition switch): 0.5v
Battery to reg/rec (permanent live): still at 12.9v

I gotta figure the only possible culprits are the wiring from the battery to the ignition switch, or the ignition switch. But since the voltage has already dropped from 12.9 to 12.7 at the ignition switch (with it off), that the wiring is at fault? And when I hit the switch, the resistance in that wire grows and the voltage drops down. It doesn't drop at any other battery live, only at the switch. Would you conclude the same? Would you also conclude it'd be easier to run a new live wire up to the ignition switch than tear the wiring loom apart to repair the old one?

Thoughts much appreciated!
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CBR600 (1988) | GS500 (1989)

[stinkwheel]

Just to check you're using the multimeter correctly.

So you have the black lead earthed by connecting it to either the battery negative (best) or a piece of bare metal on the frame and you have the red lead on the connector leading away from the ignition switch?

And you're NOT testing the voltage across the terminals of the ignition switch which would give the results you describe on a normally functioning bike.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Nipedley]

Hey stinkwheel

Yeah I was using negative lead on the battery terminal, I did manage to answer my own question and find out why..

Resistance on the live wire to the ignition switch was 40k ohms ! And I ripped what looked like factory wiring conduit apart to find this (piccy below)

That's the wire to the ignition switch that's badly crimped, it's not even falling out, it was crimped like that. They also cut off 3 connectors (reg/rec and headlight) and stuck the bare pins in, so I guess it's time to sort out the wiring.. The funny thing is, I've had this bike for 4 years and done 12,000 miles without a hitch, crazy it lasted that long.

The even funnier thing is, when I finally had a problem with it, I started the bike absolutely fine, hopped on and only when I flicked the headlights on did the bike die (and has been dead since), it must have been the last straw
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CBR600 (1988) | GS500 (1989)

[Nipedley]

And the other end... !
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CBR600 (1988) | GS500 (1989)

[Raffles]

I experienced similar symptoms with my bike yesterday. It turned out to be a corroded terminal underneath the main fuse.
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A good loser will always be a loser.