1982 xj750 seca aux light being funky

So my aux light is not working. It is among the last two things I have to get working in order for the bike to be completely operational. Not a big deal but I'd still like to figure it out.

I tested the bulb in its reflective housing and the bulb works fine (the voltage across the power supply system drops about 2V). I tested the wires from the motorcycle and they put out about 10.5V when the aux beam switch is "on" and 0V when the switch is off. I made sure to clean the connections which looked good in the first place but when I connected the wires, the light doesn't work and the voltage drops to zero.

Everything else is working on the bike except the 5A fuse for the brake lights is blown. The only thing I can guess is that perhaps the battery isn't cranking out enough amps.

Any ideas?

Thank You

 

do you have a ground wire attached to your aux light? I think from the factory they grounded through the housing. Just a thought to check and make sure you have ground.

When I got my 750 it already had a ground wire run for it separate.

 

Yes, it is grounded to the housing. I've been working on the problem more today looking for anywhere where there could be a short circuit. I even took apart the right handlebar control unit and resoldered the connections to the switch (they looked a little crappy).

Still no good. The sleeves around the wires all looked good. As far as I know, the wire just loops back to the super high tech LCD display. I will look there tomorrow, but that is the only other idea that i have.

 

both my 750 secas have a red and black wire couming from the housing, so no internal or mechanical ground. they both run into the headlight area wiring and get power and ground there.

 

I stand corrected, there is a black ground wire from the factory.

R/B and B connect in the headlight bucket.

 

Yeah, that is the way it is on my bike too. Coming from the bucket, there is a R/B positive and a Black that hooks into the same coupler as the flashers and brake fluid sensor. Still can't find the problem. I've been trying to figure out what direction things are going in the wiring diagram to narrow down my search, but I'm stuck there too.

Does anyone know a systematic way to track down a short circuit?

 

Get an ohm meter and measure across R/B and B, tell us if you get open circuit or an ohm reading.

You SHOULD get an ohm reading (the bulb) if open then you have a borked bulb, or a broken wire.

 

A short (from positive to ground) would blow a fuse or melt wire insulation. In your original post you said you already tested the bulb (I assume directly connecting it to the battery) and it works. Then you said that you "tested the wires from the motorcycle and they put out about 10.5V when the aux beam switch is "on" and 0V when the switch is off". Was this test at the R/B and black wires at the aux light? If so then the bulb should light (but might not be that bright at 10.5v - looks like your switch and the in-line wire connectors are dirty, giving you about a 2V drop).

FWIW - Harbor Freight sells rectangular fog lights with 55w H3 bulbs that will fit directly in place of the aux light and it does not have the shield around the bulb that creates the "tailored" OEM beam pattern. Both clear and amber.

 

Yes, I tested the light which worked, and I tested the red and black wires going into the housing. What I assumed about electricity is that it takes the path of least resistance which is why it would show a voltage when there is no resistance present and show no voltage (electricity is routed to a different, short, circuit) when a load is applied.