Rear Turn Signal/Brake Light Issues

[adistler1]

The next thing to tackle on the new 78 FJ40 is a turn signal/brake light issue. Everything is in working order, except for the rear passenger turn signal and brake light and the front drivers side marker light.

When I turn on the lights, everything lights up including the rear passenger taillight. When I hit the brakes, the rear passenger brake light does not work. When I do the right turn signal, the rear passenger turn signal does not work. When I turn on the hazards, everything works but the rear passenger.

The windshield wipers work fine. The horn does not work at all.

I have checked all fuses and changed out the bulbs, but that's as far as I've gone because I know absolutely NOTHING about electrical.

I did notice that on my drivers side marker light that one of the wires needs to be cleaned up and soldered. It's broken free. I didn't know if that might be the issue in completing a circuit or if it could be something else.

 

[John Smith]

The main thing you need to know about FJ40 electrical issues is to always check the ground first, it is usually the culprit. For tail light issues you may also have completely corroded connector pins that have rotted away to nothing. Pull apart the connectors for the rear signals and inspect. Since you eliminated bulbs as the problem by replacing them all focus on bad grounds.

 

[adistler1]

The main thing you need to know about FJ40 electrical issues is to always check the ground first, it is usually the culprit. For tail light issues you may also have completely corroded connector pins that have rotted away to nothing. Pull apart the connectors for the rear signals and inspect. Since you eliminated bulbs as the problem by replacing them all focus on bad grounds.

Would I start by pulling the housing out? Like I said, I don't know the first thing about electrical. I don't know where to find the ground. I see the wire coming out to the back bumper and there are some connectors and lots of tape.

 

[John Smith]

Yes, pull the entire housing so you can check the condition / connection of the wires.

 

[Tim71FJ40]

The electrical systems in these trucks are very simple. In general, a light ( for example) needs power and ground. A complete circuit is a power source to some device (a light, a heater motor, windshield wiper motor) to ground. "Ground" is going to be a good, clean, metal surface - body, frame... There also used to be grounding blocks that everything tied back to.

You do not get a complete circuit or current flow without a good path to ground. Some of your dash lights are grounded directly to the metal dash when the light housing is inserted into the dash hole and tightened down. Some lights will have a separate ground wire that needs to be connected to a clean solid ground point. Some people can't get a consistent ground and will solder a wire to the outside light housing that should be grounded to the truck and run the wire to a better ground point.

So whether your switch is providing 12V when activated or whether it is switching the ground in and out of the circuit (like the wipers) a complete circuit is always power, device, ground.

Since a good ground relies on good wires, connectors, and a clean (no yuck, no rust) metal surface... Ground issues will be 90% of your electrical issues on there rigs.

We need to rule this out before we tear into the next thing to check.

Hope this helps a little.

 

[adistler1]

I pulled out the housing. This is what it looked like. I pulled the ground off the light and cleaned it a bit and reattached it. I didn't remove the ground bolted onto the metal inside the bumper. Nothing changed. Here are some photos of what I have going on back there.

 

[Tim71FJ40]

Do you have a digital multi-meter? It will help troubleshooting a ton if you do. They are pretty inexpensive and extremely valuable.

With a meter you can test to see if you are getting 12V when you are expecting it. If you are but still no light then you have bad bulb or bad ground. If you don't have 12V when you expect it then it doesn't prove you have a good ground but you know that one problem is further up the circuit on the power side.

If you don't have a meter we can improvise.

 

[adistler1]

I have access to one, I believe. It might be next week before I can get my hands on it though. Do I just touch each wire?

 

[John Smith]

I pulled out the housing. This is what it looked like. I pulled the ground off the light and cleaned it a bit and reattached it. I didn't remove the ground bolted onto the metal inside the bumper. Nothing changed. Here are some photos of what I have going on back there.

Nice... A PO has butchered your wiring. The hose clamp is a new one, but I have seen wire nuts used before. You need to trace those wires to where they meet the factory harness and see what nightmare is on that side. I would get out the soldering iron, some wire, and fix that whole mess now. The wire nuts need to go and I bet you find some more terrible work where this meets the factory harness.

 

[jdayment]

I had a similar issue and i ended up having to replace some wires in my harness due to thePO butchering my harness i had wires fused together behind the dash that was the culprit.

Sent from my iPad using IH8MUD

 

[adistler1]

The entire rear end is a hack job. I can't unlock the tire carrier to even open the door.

 

[Tim71FJ40]

You probably want to clean it up. I think most people would but be careful if your not comfortable yet with wiring.

Trace one circuit at a time. Hack job or not the light still operates the same way. You need to get voltage when you expect it and ground the lights.

 

[adistler1]

With the meter do I hold the black to metal and the red to the wire? I've never used one.

 

[Tim71FJ40]

Set the meter to measure voltage. Set the scale to a setting over 12V. Touch the black lead to a good metal ground. Put the red lead to the bare wire or connector where you are expecting the 12V.

Not you need to set the condition under which you are expecting the light. If its a taillight, pull the light switch. If its the brake lift you need someone to step on the brake.

You need 12V at the input. Your meter is measuring the voltage prior to the light and you are providing a new path to ground. If your ground point is good and you are getting 12V at the input, then you will read 12V on the meter.

If you don't have 12, then the problem is further upstream. If you have 12 and still no lights, then the problem is downstream.

 

[sggoat]

Those pics of the tail light ground show a very suspect connection. I would remove the clamp and wire, clean the case,(down to bare metal), then resolder the ground wire. The terminal end connection is not good either-remove it, clean to metal(get all the corrosion off) reconnect(make sure to check inside the crimp connection on the lug) I might just snip it off and install a new lug

 

[Tim71FJ40]

Agree completely. Almost always a ground issue. But play with the meter and get familiar with it. Down the road you'll be glad you did when you decide to re-wire the whole truck.

 

[adistler1]

Thanks for all the help, guys. I plan on getting into this tomorrow.

 

[Tim71FJ40]

Did you ever get them working?

 

[peesalot]

That ground sucks. Use a piece of wire, new, put one end under hose clamp and other to a clean ground.
Use test light with probe to verify power at light, under those household wire nuts.
If good there then with a good ground your done.
If no power there then follow it back until find issue.
The blink and brake use same wire if that helps.
you should replace those wire nuts with some automotive disconnects.

 

[AlexJet]

I'd get rid of those yellow twisters and do a proper wiring. Ground is not a promising point on your picture either.