Electrical issues

[MccMason]

There's been multiple variations of my problem on here, which has been helpful, but I haven't really found the exact thing yet. I'm looking for a little trouble shooting guidance. I have a 1973 Bronco and my rear lights don't work at all. No brake lights, no tail lights, no blinkers. My headlights work, my front turn signals work, my front hazards work. My fuses are good, my brake pedal switch is good, my next spot I'm going is the turn signal switch. Is there a good way to diagnose that without just replacing it? Or should I check anything else? Also, does anyone know how power is routed for the rear lights? For example, from the battery, through the fuse box, to pedal switch, up the column, etc. Any help is appreciated, this is my first Bronco so I'm still figuring everything out. Things have been updated but its an original column, original wiring, original dash. Thank you!

 

[ared77]

You've come to the right place! I don't have wire color code info but others on here will chime in soon with what exactly to test. I'd think, because you have no tail, brake or turn signals, culprit could be the turn signal switch. Unless you have no ground for the rear lights, not likely but had to add that.

 

[Bruners4]

My first check would be with a verified working test light with a good ground. Then remove the taillight bulb from it's socket. Use the test light probe to check each of the little button terminals that make contact with the little contacts on the bottom of the bulb. When the taillights are on. the test light should illuminate as the filament in the bulb would. Same for the brake/turn signal contact. If the test light doesn't illuminate, without moving your ground connection, verify that the test light is still working. If the test light works when verifying it, then battery positive is not reaching the contacts in the bulb socket. If the test light does illuminate, replace the bulb, verified working, and test the outer surface of the bulb socket while the tail or brake/turn are turned on. If the test light illuminates during this test, the ground is missing for the bulb socket. Note that there can also be a loss of connection between the base of the bulb and the bulb socket that will also appear to be a bad ground.

Yes, the turn signal switch could cause the Brake/Turn signal light to not illuminate, but not the taillights. Checking the turn signal switch column connector with the test light on the correct output wires would show this.

 

[Bruners4]

And Welcome to the forum.

 

[Oldtimer]

If front turn signals are working, the turn signal switch may be OK.

After checking grounds at brake light housings, I would check harness, from firewall to rear of Bronco.
May be damaged by rocks, or chewed on by rats.

Driver side between firewall and inner front fender is where the harness to rear of bronco plugs into dash harness.

The single connector is black/red stripe for backup light power.
The quad connector has
Brown wire, running lights
Green wire, Right turn/brake light
Yellow/black stripe wire, Left turn/brake light
Orange, fuel tank sender
If you have an auxiliary fuel tank, there will be a single Yellow wire from its sender.
The yellow wire goes thru open hole in fire wall below the above harness.

The harness that runs to rear, down inside of frame rail, has a connector in the driver rear wheel well just in front of shock mount.

Here is link to seabiscuits excellent schematics: http://seabiscuit68.tripod.com/

 

[chuckji]

You didn’t mention, are the tail lights LED?
How about the reverse lamps, do they work?

 

[MccMason]

Thank you guys for the help, I’ll keep on working on those. The entire tail lights are new but are not LEDs. There is also not a ground on the taillight buckets themselves. Should there be or do they ground through the mounting hardware?

 

[MccMason]

Update: found some broken wires along the frame rail this morning, obviously a problem. I’ll splice it all back together tonight and see if that fixes it. Thanks again!

 

[DirtDonk]

Should there be or do they ground through the mounting hardware?

They do ground through the mounting screws to the body. But on a 73 I thought there would’ve also been a separate ground wire attached to the body inside the taillight cavity.
Do you see a screw hole or a wire hanging anywhere?

 

[MccMason]

They do ground through the mounting screws to the body. But on a 73 I thought there would’ve also been a separate ground wire attached to the body inside the taillight cavity.
Do you see a screw hole or a wire hanging anywhere?

No, not that I noticed. I'll take another look to double check though.

 

[DirtDonk]

Actually, I think I was corrected recently and that ground is for the running lamps? I can’t remember, but there is a wire in there. Maybe I thought it was for the tail lights because it’s part of the same harness.
I think I even said during that conversation, that I was gonna have to dig back into mine to see what I was talking about!

 

[MccMason]

Actually, I think I was corrected recently and that ground is for the running lamps? I can’t remember, but there is a wire in there. Maybe I thought it was for the tail lights because it’s part of the same harness.
I think I even said during that conversation, that I was gonna have to dig back into mine to see what I was talking about!

No worries, i appreciate the help either way. For the record, i fixed the broken wires along the frame rail, there was no individual ground on the tail luck buckets and my lights are now working!

 

[ared77]

Congrats!!!!

 

[joebronco73]

They do ground through the mounting screws to the body. But on a 73 I thought there would’ve also been a separate ground wire attached to the body inside the taillight cavity.
Do you see a screw hole or a wire hanging anywhere?

I know OP has resolved his issue, but I've got a '73 and it's got me curious. If the license plate light is self-grounding, are the rear running lights grounded through it as well? I don't have the schematics handy to check...just a passing question in my head.

 

[DirtDonk]

The license plate lamp should have two wires. One power and one ground.
They figured the tailgate itself was not a reliable ground, so ran a ground wire down to the body underneath.
Double check yours and make sure it’s got two wires.
But as Oldtimer mentioned in another thread, there were different bulbs (or was it sockets?) listed by Ford.

Can’t remember where the running lights ground. But maybe that’s the ground wire in the taillight cavity that I’m thinking of.
Do yours all work?

 

[Oldtimer]

Different bulbs and therefore different sockets, but they all had a dedicated ground wire in the pigtail that went from light assembly to a sheetmetal screw.

 

[joebronco73]

The license plate lamp should have two wires. One power and one ground.
They figured the tailgate itself was not a reliable ground, so ran a ground wire down to the body underneath.
Double check yours and make sure it’s got two wires.
But as Oldtimer mentioned in another thread, there were different bulbs (or was it sockets?) listed by Ford.

Can’t remember where the running lights ground. But maybe that’s the ground wire in the taillight cavity that I’m thinking of.
Do yours all work?

Mine does, however, PO did some roadside wiring it seems and I've got a license plate light on order. Just got me curious, since I didn't see a ground in my tail light assemblies...maybe I did and just didn't catch it. The mystery continues!