Brake Light / Running Light Issue

[Okie69]

Alright guys. I’m a little stuck fighting electrical gremlins. Here’s what’s going on.

I have headlights as well as front and rear turn signals the indicators flash at normal speed with the turn signal stock. The hazard switch turns on both sets of flashers but they flash quick and dim. I don’t have running lights or tail lights at any time, and I don’t have brake lights ever. I’ve also lost the gauge cluster back lights. I don’t know if that’s related.

What I’ve done. I started just trying to work through the brake light circuit.
-All fuses are good
-The red wire going into the brake switch has power.
-The brake switch closes and opens as it should (verified voltage passing through as well as checked ohm readings).
-Checked the red w/black wire that goes to the turn signal connector and then to the emergency flasher switch has power when the brake switch closes.

Jiggling the turn signal stalk or the wires running up the column has no effect.

 

[Jdgephar]

Something after the hazard switch must have a short. Higher than normal current causes the flashers to go faster, as the bi metal heats up faster with more current. However, not enough to open a fuse.

Maybe something in the gauge cluster wiring, since the turn indicators are there and light up with the hazards (not sure why turn signal works normally)

Edit: the more I look at the diagram, I'm thinking it is an issue in the turn signal switch in the steering wheel. What year do you have?

Sent from my SM-G981U using Tapatalk

 

[DirtDonk]

Could be turn signal AND headlight switches.
The lack of running lamps and dash illumination can come from a failed/faulty headlight switch, but the illumination can also be the small fuse in the panel or the rheostat not turned up enough.
If it’s an original ‘66 switch it might have it’s own fuse piggyback on the switch itself.
However that would probably make the headlights not work.

Since the hazards work (sort of) you know the wiring between the column and the back are at least partially intact. But aside from the switch, some buggered wires along the way or bad lamp sockets could be the cause of the short.
I would at least verify that all the tail lamp sockets on wiring are good first. Not because they’re higher on the list, but mainly because they’re just easier to check!

 

[Okie69]

Something after the hazard switch must have a short. Higher than normal current causes the flashers to go faster, as the bi metal heats up faster with more current. However, not enough to open a fuse.

Maybe something in the gauge cluster wiring, since the turn indicators are there and light up with the hazards (not sure why turn signal works normally)

Edit: the more I look at the diagram, I'm thinking it is an issue in the turn signal switch in the steering wheel. What year do you have?

Sent from my SM-G981U using Tapatalk

It’s a ‘69.

 

[Okie69]

Could be turn signal AND headlight switches.
The lack of running lamps and dash illumination can come from a failed/faulty headlight switch, but the illumination can also be the small fuse in the panel or the rheostat not turned up enough.
If it’s an original ‘66 switch it might have it’s own fuse piggyback on the switch itself.
However that would probably make the headlights not work.

Since the hazards work (sort of) you know the wiring between the column and the back are at least partially intact. But aside from the switch, some buggered wires along the way or bad lamp sockets could be the cause of the short.
I would at least verify that all the tail lamp sockets on wiring are good first. Not because they’re higher on the list, but mainly because they’re just easier to check!

The brake lights use the same filament as the turn signals right? So don’t I know the wiring to the back is good because of the turn signals working?

I’ve got a new headlight switch on order. Might need to get a turn signal switch too it looks like. I need to tear into the column and replace a worn out shift collar anyway.

 

[BigBronco16]

Check all grounds and make sure they are clean and well connected. Corrosion/rust can really play havoc with this. All my gremlins have been traced back to a grounding issue. Good luck.

 

[Rustytruck]

swap the 2 flasher units and see if it changes. check the mounting screw for ground at the high beam switch on the left front floor. check the harness ground drivers side rear frame back at the frame horn. do you have a separate ground from the negative battery post to the body tub?

 

[Okie69]

swap the 2 flasher units and see if it changes. check the mounting screw for ground at the high beam switch on the left front floor. check the harness ground drivers side rear frame back at the frame horn. do you have a separate ground from the negative battery post to the body tub?

I do have a ground to the body and to the frame at the front. Haven’t checked for a rear ground.

I’ll check your other suggestions when I get back to the house later.

 

[DirtDonk]

Yes, from the turn signal switch all the way back to the tail lamps the turn, brake and hazards all use the same wires, socket contacts and filaments. But because it seems like you have a short somewhere, that’s why I said to closely inspect all those things so they don’t create false readings when you’re checking other things.
But checking and renewing the tail lamp socket grounds is a great suggestion. Lack of grounding can cause the current to go hunting for another ground path and that could end up being something in the housing. Also giving you strange readings.

The highbeam switch on the floor does not have a ground. It works even when unbolted. It is simply a pathway for 12 V to pass either from the light switch to the low beams, or the light switch to the high beams. The grounds are all up at the lights themselves.

 

[Okie69]

I’m about ready to just add a half dozen grounds in various places on this thing.

 

[Rustytruck]

Very important grounds battery to engine block, battery to sheet metal, mounting base for starter solenoid. voltage regulator to body sheet metal, back of head to fire wall. wiring harness to dash, frame to wire harness at drivers side rear. light buckets to body. if you run a 3G alternator alternator case to engine block ground since you loose the stock regulator connection.. dash to gauge cluster. there are more grounds like courtesy light to windshield frame and ground to defroster/heater motor. you really need good ground frm the battery to the body tub especially if all your factory body seams are really rusty.

 

[Okie69]

Well all I had time to do tonight was switch the flashers around. When I did the turn signals went from a ~1 second on off cycle to ~1/2 second on 1/2 second off. It could be in my head but they seemed brighter on the shorter cycle. Which makes sense I guess.

I seem to remember about 1 second on 1 second off being normal but I’m not sure.

 

[Okie69]

Alright so I got the new turn signal switch, headlight switch, and flashers in. This is what happened.

Turn signals:
before new parts all turn signals good.
After new parts all work except front driver and the left turn signal indicator in the gauge cluster.

Hazard lights:
before new parts quick and dim flashes
After new parts clicks heard but no lights flashing except for very dim gauge cluster lights and very very dim front right indicator ammeter jumping wildly across full gauge

Park lights:
Before new parts nothing.
After new parts very dim light at front right indicator comes for a split second then off and repeats. Same clicks heard and same wild swings of the ammeter.

Headlights/ taillights:
before new parts headlights worked. No taillights .
After new parts headlights work. No taillights.

Found a number of wires behind the dash that looked like they had been nibbled on but not bad. Repaired those. Found a ground at the rear Driver side that wasn’t connected fixed that. Ran a ground to front indicator light cup.

Jiggling wires behind the dash doesn’t change anything. (Hoped to move them and see a change indicating a short)

Clicking seems to just be from the gauge cluster but I’m not sure. It’s not the flashers when the ammeter is going nuts.

Also I found this and cannot find where the other end of it is. Any ideas? On left hand side of the image which is heading off to the left of the dash it’s a black w/red wire and an orange w/yellow wire. On the right hand side it’s orange w/yellow, Black and yellow w/black. The yellow w/black wasn’t connected and I couldn’t find a matching end further up the harness.

I did find out that if it (yellow w/black wire) touches ground it pops the turn signal fuse.

Don’t judge those grounds they were the infamous previous owners doing!

 

[DirtDonk]

Dunno, but that busted up Yellow wire sure looks important-like!
For general purpose discussions with Broncos, any Black w/yellow stripe wire is always hot, directly to battery and should be treated carefully.
The big black blob in the middle of the pic is a standard Ford molded splice. In your case, looks like a ton of wires in that one.

A Yellow wire that I'm familiar with off the top of my head is constant 12v power for the ignition switch. If there is a Black w/yellow wire in that splice then you can pretty much guarantee that they all have power all the time. But that does not sound right, so maybe you can call out all the colors that are in that splice? Most of the big splices can be categorized into two groups. Switched, and Constant 12v. Not sure about that one until you say what colors are included, and which wires are just running next to it.

Is the big Black wire behind the splice the one with the yellow stripe? If so then that's your main power wire-loop between the alternator and battery. With all constant 12v sources tapped/spliced into it at one point or another along it's length. It powers the constant 12v fuses, the ignition switch, the headlight switch, and probably a couple of other things.

Nice wire nut in the background. That a PO ground, or another circuit?

Paul

 

[Okie69]

I put a lot of work into that post and you just skimmed it huh?

So the black behind isn’t part of it. It’s just the orange w/yellow and black w/red on the left side of the splice then the yellow w/black, orange w/yellow, and black on the right side of the splice.

That wire nut is a temporary splice I just did for a chewed up wire on the brake switch. I’ll make everything pretty after I know the problem.

I should check when it has power but I got frustrated and came inside haha

 

[Okie69]

Oh if you were asking about the clear plastic wire nut in the background that has been like that since I got the bronco so who knows.

 

[DirtDonk]

Of course! Didn't have time to really dig into your symptoms that time, and did not even have my diagrams to list out all the functions of the other wires you mentioned. Just touched on the basics.
And no, funny as it is, I didn't even notice the clear nut. Was thinking about the orange one in the back! Unless that's some other kind of fitting and just looks like a wire nut?

Anyway, hopefully I can actually help a little, a little later.

Paul

 

[Okie69]

A little more information. The yellow wire with black stripe mentioned above is keyed hot. I still can’t find where it goes.

**Edit: apparently the black with blue stripe is the map light**


I found this over by the gauge cluster unplugged. It goes to the position on the headlight switch circled in red.

 

[DirtDonk]

Also I found this and cannot find where the other end of it is. Any ideas?

You were referring to the Yellow wire, correct?
As mentioned, could be power for the ignition switch. But it might also be power up to the horn button.

On left hand side of the image which is heading off to the left of the dash it’s a black w/red wire

Leave it to Ford, for using this color for grounds in some areas. But under the dash the only thing I can think of is the power source for the backup lamps
There is also a Black w/orange stripe that could have faded to red, so to speak. That's power to the headlight switch I believe.

and an orange w/yellow wire.
On the right hand side it’s orange w/yellow,

Listed as "#8" in the old chart, but with no 8 showing in the actual diagram. Still looking in the newer diagrams for '72 and later.

Black and yellow w/black. The yellow w/black wasn’t connected and I couldn’t find a matching end further up the harness.

I did find out that if it (yellow w/black wire) touches ground it pops the turn signal fuse.

In early diagrams it is for the Left Side stop/turn lamp. Later diagrams it disappears, so looks like one they changed. You can check this at your rear housing to see if it's the same color.
Would explain why it blows the fuse though.

Paul

 

[DirtDonk]

A little more information. The yellow wire with black stripe mentioned above is keyed hot. I still can’t find where it goes.

Check both turn signal wires, but should be left according to the diagram.
You can check either at the lamps, or up at the firewall, or wherever. If you don't have this color wire in your new turn signal switch it's likely due to the manufacturers using only the later colors and not the early.

**Edit: apparently the black with blue stripe is the map light**
I found this over by the gauge cluster unplugged. It goes to the position on the headlight switch circled in red.

Yes, it would have been in all the harnesses whether that option was checked or not. If the buyer wanted it all they had to do was mount it to the dash and plug it in.
Same for later years ('73 and later I think?) up at the wiper motor where there was an extra plug for a dome light if they got that option. But if not, the wire was still there.

You can verify your conclusion by measuring for voltage at that wire with the headlight switch knob twisted all the way until it clicks. Just like a dome light on other cars, you should see 12v at that wire when the knob is twisted.


Paul