electrical gurus pleae help!!!

[Land Schmoozer]

'64 FJ40
front lights all work fine
rear license plate light works fine
brake lights work fine

however... no tail-lights (running lights) and rear turn signals both blink about half power regardless of which light should be on...

ok so you take out one of the rear bulbs other turn signal works fine... but never any running lights and they are on the same power line as the license plate light...

grounds are all good... metered them...

any ideas???

it the brake lights are working off the top filament of the bulb... i assume the running lights should be running on the bottom filament...

any suggestions w/b helpful... two of us spent 4 hours with a meter testing this and that and they should work... but put that second buld in and nothing.... makes no sense!!

thanks!
casey
'64 FJ40, '83 FJ60, '97 Tacoma

 

[Pin_Head]

It is what is known as a "ground loop" problem. The light case ground is bad, so the current runs through another filament (like brake or running lights) until it finds a good ground. It is hard to find this type of problem with a meter. You would have to remove the bulbs and have a meter that can accurately measure resistance in the 0-10 ohm range. Try running a separate ground wire from the light case to the frame and see if your problem goes away.

The running lights may be a separate problem if they are outside of the tail light/turn/brake assembly. Do you have 12V at the bulb? If so, how many amps with the wire sink when you ground it through the filament or a 10 ohm resistor?

 

[skyshark186]

Pin Head seems to have a much smarter answer than i do.

Mine did the same thing, the PO had some nasty looking wiring going back to the lights. One of them was only connecting on three out of the six internal wires. Cut the bad sections out, layed in new ones and presto. Blink like mad now.

 

[Steve C]

Ok, as a recovering engineer, here are a few suggestions for wire tracing:

1. Get a volt meter, set it up to measure 0-15 VDC (or so).
2. On the positive probe sharpen the tip so you can poke through wire insulation and extend the length of the probe to about 10-15 feet ( the size of your cruiser).
3. On the negative probe, have a clip that can attach to the negative terminal of the battery, and also the 10-15 feet of wire. (don't worry about the length effecting the measurements, it won't)
4. Clip the negative probe on the battery. This establishes the point of reference for all other measurements. You never need to move this one.

5. measure the battery voltage with the positive probe. This will tell you what the max voltage to look for will be. (It will be 12-13 volts)

Now you are set up to look for where the volage is dissapearing.

6. With the BULBS STILL IN (sorry, not yelling) and the lights on. poke through the insulation of the wires and measure the voltage right before the wire goes into the light assembly. If it is more than a little below the battery voltage, then the voltage is lost in the positive path from the battery through the switches, then to the wiring to the back. If it is right around the battery voltage, pull the bulb out and look at the connections, do they look OK? If so, put the bulb back in and sneak your probe in to measure the voltage at the outside of the case of the bulb (the negative terminal). If the outside metal part on the bulb is much above 0 volts (which sounds like the case) you have a ground problem.

Dont forget to put some liquid electrical tape on the little holes you poke.

 

[Land Schmoozer]

guys thanks for the suggestions... will be trying them this weekend... going to go out and get a good (digital) meter... will be easier on these old eyes to see!

casey

 

[warpdriv]

On my 1/71 I had a random brake light outage. I ended up being in the turn signal switch. Not sure about how a 64, but just a suggestion.

HTH,