Chasing Electrical issues (1 Viewer)

[FJ rookie]

I recently purchased my 1980 FJ40 - non US model. After the first day or two of driving - testing all the switches etc - my head lights would not turn off. I have learned the headlights are connected to both the turn signal/ high beam and hazard switches. I have isolated the issue by removing fuses, and determined the the lights turn off when I pull the turn signal fuse. So, I am getting constant power from somewhere in that circuit. I am not the best with electrical, looking for ideas on where to look. Turn signals all work properly, as does the hazard lights.

All other market lights, dash lights etc work as intended including High Beams

 

[ceylonfj40nut]

First make sure you every ground on your truck works! Number one issue for your symptoms!!!

 

[South Texas 97]

If not already done so go to @Coolerman ‘s site and get the electrical diagrams for your year, model of truck. You should be able to trace the circuit with that diagram. Take your time, and if you don‘t already have it grab a test light and a cheap multimeter

 

[charliemeyer007]

Some times switches go bad inside. On my 72 I have taken several of them apart and "fixed" them. I had my wiring diagram blown up to like 24x18 and then laminated - very handy. +1 for a test light and VOM

 

[Malleus]

24x18? You're eyes are way better than mine. I had mine blown up to F size. That's 28x40 for you non engineering types.

I'd kill for lamination. Back when I was in the field, we used up yards of what we called combat acetate, for maps. I'd kill for a roll of that stuff. (Side note: I asked a Marine buddy if he knew of a source for it once. He asked, " is there such a thing as non-combat acetate?")

 

[45Dougal]

Your headlights shouldn't be powered through the turn signal fuse. Check which fuse is which. Test for volts on them all - appearance is often misleading - even if they look good, they are often bad.

If the turn fuse really is powering them then it sounds like someone has either hacked your wiring around, or your harness has overheated at some point and you now have a short circuit between wires.

With the turn fuse removed, can you switch them on with the switch?
Yes - sounds like a short circuit in the harness
No- maybe the wiring at the fuse panel is modified

Removing your headlight fuse should kill them.
If this is the case then it may just be a bad switch - reach up underneath and unplug the connector from it - replace the fuse - are they now off?

Yes - your switch needs a clean out.
No - you have a short circuit downstream - possibly where the harness goes through the bulkhead or around a tight bend.

Try adding some photos of your fuse panel wiring, headlamp wiring, and your harness near the bulkhead

 

[45Dougal]

First make sure you every ground on your truck works! Number one issue for your symptoms!!!

Which bad ground would cause the headlights to stay on?

 

[FJ rookie]

Ill add some pictures next week when I have time to work it again. Head light fuse - bottom of the 8 slot panel - does not turn off the headlights. Number 6 slot should be the turn signals per haynes manual. Headlights turn off when fuse is pulled. Started checking grounds around the front end with my multi meter. Wiring in the engine bay is not factory. Wiring under the dash appears to be.

With positive lead on the battery, driver side headlight shows 11.4 volts( yes I know this is low but not my current issue ) on all three wires/connectors. Battery reads same terminal to terminal. Passenger side does not respond the same way. I am thinking I have a short in between the two lights - wiring comes from the passenger side to the driver side.

 

[FJ rookie]

Ill test the turn signals with fuse pulled and respond.

 

[45Dougal]

Sounds like you have an earlier fuse box, so maybe the fuses are not exactly as listed.
My guess is that pulling the turn fuse does not kill the turn signals but only the headlights.

Both head lights are connected in parallel so should come on together - maybe you have a loose connection. Do they both come on in any way?

Do your tail lights function normally?

You say that you have battery voltage at all terminals on the headlight connector - this suggests that both high beam and low beam are both on while the switch is off.

The only single fault that can cause this is the high/ low switch on the steering wheel.

Try jiggling the high low switch a few times and otherwise spray some contact cleaner inside it - you might need to remove it and clean it out

 

[45Dougal]

An easy thing to try is to unplug your steering wheel connector - that should isolate the faulty switch