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Discussion Starter · #1 ·
On my 83 vt750 if I apply the foot brake OR hand brake, all the lights dim. This suggests there's a short somewhere. I tried using a different "stop sensor" box (from my parts bike) that sits under the air filter box because I thought maybe that thing had gone bad, but still the same result. I guess they both could be bad. Does anyone know how to test the stop sensor?

All other electronics still work fine. The only thing I've changed electronically is adding a ground wire to the metal plate on the bottom of the fuel pump because there must be a loose ground connection and it wasn't always pumping when it should have been. I don't think this should be related to the brake light but who knows.

I guess the light bulb could be bad but I don't understand how that would create a short and pull so much current that all the lights dim.

thanks
 

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Well definitely not the bulb. I guess it's time to bust out the wiring schematic and try to track down the problem. Any other thoughts?
Maybe a bad ground? I know on trailer lighting; if you have a bad ground to the trailer, when you use a turn signal, the opposite signal dims when the other side is lit.

Just a thought,
Phil
 

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Dollars to donuts you have a short. I'd start tracking back from the brake light. Betcha find a bad (bare) spot.
 

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Remember, the 83 has "tail light" idiot light...in instrument panel. Check that circuit for short as well.

IDK, water in light bulb?
 

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My money is on a weak ground. Good enuff to handle a small load but you add more to it and all lights dim.

Yeah, I'm leaning towards a ground issue too. With a short, you're gonna' blow fuses, and with an open circuit/connection you're gonna' get nothing.

Phil
 

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Discussion Starter · #9 ·
Remember, the 83 has "tail light" idiot light...in instrument panel. Check that circuit for short as well.

IDK, water in light bulb?
Yeah, so is the idiot light supposed to light up when the tail light is NOT working, and is it affected by the brake light circuit?

Also I'm leaning towards a bad ground somewhere too. Still searching....
I wish the wiring diagram was in color. I'm thinking about photo-shopping it in color. I'll post it if I ever follow through with that idea.
 

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Discussion Starter · #11 ·
UPDATE:
I hate when people don't update their own thread with the solution they came to. Well mine turns out not really be a "solution" but a good story about a dumb a*s. So it turns out that I had accidentally swapped the fuel pump wires with the front brake light wires. This in turn did something bad to the fuel pump relay thing because it was getting a bit hot. Luckily I had another relay I took off my parts bike. In the process of things I checked the indicator box and the taillight failure box and they both worked fine. I also found the brake lever switch up at the handlebar had broken and I again had a spare part I could use. So now everything works. I still however, notice a very slight dimming of lights when the blinker flashes or the brake light comes on. More so when I have my brights on so I think there is probably still a weak ground somewhere, but I'll worry about that later (last famous words).
 
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