why does my running light have 2 Volts

[rubyasaurus]

Thanks to everyone for all the help with my carbs, its running great.
My tail light is not working, and dont really want to get pulled over, (manual didnt seem too helpful) is it only suposto have 2 volts, it seems to have a different resistor than the brake light which works fine. Is it possible I just have the wrong bulb?

any help would be greatly appreciated, I have beeen avoiding night cruising and its starting to bug me.

Thanks
Tim

[CatatonicBug]

What bulb do you have? It should be an 1157 (dual filament) bulb. One filament can burn out at a time. Try swapping it for another known-good bulb to check the circuit/connection. They're pretty cheap, and you should have a couple spares handy anyway.

[rubyasaurus]

I have been trying a 2057 bulb, but it makes contact (seems the same, dont think its the problem) have chaecked the voltage at the terminal and it is only 2 volts,I checked V at the the plug under the seat (black, ground was good ..white brake tested 12 volts with the pedal depressed...blue, tested only 2 volts).
now that I have the light off, I see some idiot put electrical tape instead of shrink on some joints... ohh that was me about 12 years ago.

I also tested continuity and found the blue wire behind the headlight where it looks likes its ready for accessory lights, still only 2 volt, the wierd thing is while testing I did get 12 volts once but never again, what connector am I missing,\ive taken apart and cleaned every connection behind the light,

When I tested The connector under the seat that goes to the tail light(from wiring harnes), white to ground gave 1000 ohms, and the blue gave 2000 ohms, so I assume the running light runs on less volts? are the filaments different on a 1157 for the running light, or should they be the same?

I dont usually have trouble changing a light bulb.

Thanks again
Tim

[rubyasaurus]

I just found a good wiring diagram here, thaks, anybody ever have a light checker unit go?

[Just In Case]

AFAIK there is no electronics in the tail light circuit. The bulb runs at 12V. The resistance in the circuit ought to be only a few ohms, whatever the bulb resistance is.

If you're getting 2V at the fitting, you have a major poor connection somewhere in the wiring or earth circuit. Check the earth side too! Your missing 10V might be there.

The only way is to liven up the circuit and probe every connection back up the harness until you find the missing volts. I ended up replacing the multi-pin connector under the seat to sort out a low volt issue (along with a PO issue too). I've also had a layer of oxide on a fitting, which took time to isolate, then clean off. Think logically and double check before the wire cutters come out!

You can also leave the bulb in, and by connecting a wire (with a 10 amp fuse in it) with a suitable probe on it to the battery, supply 12 volts at the various correct connector pins along the harness to see if the bulb lights up. That might help track down the fault, or at least confirm your DMM results. High resistance faults can be tricky to follow at times as a DMM is too sensitive.

[rubyasaurus]

thanks

the lights are on. good advice and wiring diagrams thanks again.