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Headlight's won't work......odd

TexasDude

Jr. Member
Joined
Dec 1, 2017
Messages
66
Loc.
Dallas
So, I just bought this bronco and one of the many problems is that ALL the lights and turn signals work except the headlights. The dimmer/high beam switch turns on the little red light on my gauge cluster, but no headlights. All the orange side and turn signals work and turn on. The rear lights work perfectly. The brake lights work as well. It's just the headlights.

I can't seem to find a fuse for the headlights. I've read there isn't one and that there is a breaker box in the actual switch. However, if the switch was broken, why would all the other lights work?

Thoughts? I need to get these lights to work so I can take it to inspection.

It's a 1976 and it has bulbs on it that read HB02. Do they need a special harness for these to work?
 
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Teal68

Contributor
Bronco Guru
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Mar 28, 2013
Messages
2,566
Loc.
Inlet Beach
Since the headlights aren't flicking on and off I doubt it is the circuit breaker. First I would disconnect the headlights and see if you have power with the switch on. If you do then either the connection is bad or the bulbs are burnt.

If you don't have power then either the switch is bad or there is a short. I doubt the switch is bad since the other lights work, but I'm not 100% sure on that. Hopefully someone with more knowledge will chime in.
 

Slowleak

Bronco Guru
Joined
Sep 12, 2013
Messages
3,732
Loc.
Georgia
Does it have the original factory wiring? I have never heard of those bulbs.

It doesn’t sound like your dimmer switch, or headlight switch is the issue. The dash indicator is fed from the green/BLK wire in the dimmer switch which also feeds the high beams. The red/BLK wire feeds the low beams.

It could be ground wires. Those are normally on the radiator support. It may be something as simple as a breaker/fuse that was added, or the PO may have added relays.

Chances are any added wiring for relays is at the end of the existing harness near the headlights themselves. That’s the way most conversion kits work. Easiest way might be to get a meter and check for power along the path from the bulbs back to the dimmer switch.
 

Wyflyer

Bronco Guru
Joined
Apr 1, 2008
Messages
2,920
The good news is your headlamp indicator is working, which indicates the problem is somewhere between the dimmer & the headlamp bulb.

Here's a diagram which shows the circuitry from the light switch to the headlamps.

http://www.bronco.com/graphics/diagrams/75_77wd4.gif

I'd check the headlamp connectors at the lamp, then move back to the firewall connector next. Or look for frayed wires or bad ground at the headlamp itself. Use a tester or voltmeter for testing, the headlamps may both be bad.
 

1strodeo

Squirrel Watcher
Joined
Sep 15, 2016
Messages
3,596
Loc.
Wisconsin
Did you try a jumper wire on the dimmer switch?

I had an old Mustang and that was the only way the headlights would work, tried three different switches, weird...anyways it's a quick and easy test good luck
 

B RON CO

Contributor
Bronco Guru
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Jun 29, 2016
Messages
2,412
Loc.
Statesville, NC
Hi, to jump the dimmer I think means he bypassed it. To do that, take your test light and see which wire is hot when the headlight switch is pulled full on, to bypass the dimmer switch, feed the hot wire to one of the other wires ( one feeds the low beams, and the other feeds the high beams).
Before jumping the dimmer I would take the test light out to the left headlight and check for current. With the switch pulled all the way out, The top terminal should be hot for the low beam, and the side terminal with the colored wire should be high beam. The all black side terminal is the ground. IF there is no current out there, follow the loom in to the firewall and into the Bronco to the dimmer switch, checking for current at each connection. If there is current out there, the bulb or ground is bad.
If there is no current coming out of the dimmer switch, you can try to jump (bypass) it and if the wire is hot going in, your headlights should come on, or at lest the plug at the headlight bulbs should be hot. Good luck
 

1strodeo

Squirrel Watcher
Joined
Sep 15, 2016
Messages
3,596
Loc.
Wisconsin
Hi, to jump the dimmer I think means he bypassed it. To do that, take your test light and see which wire is hot when the headlight switch is pulled full on, to bypass the dimmer switch, feed the hot wire to one of the other wires ( one feeds the low beams, and the other feeds the high beams).

Yes thanks Ron I should've said try a jumper wire on the pigtail, not the switch itself ;D
 
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TexasDude

Jr. Member
Joined
Dec 1, 2017
Messages
66
Loc.
Dallas
Thank you so much for the help. I've narrowed down the problem. I think. Okay, the bronco came equipped with the upgraded front halogen headlight harness from Tom's Bronco Parts. Basically, the original factory passenger's side 3 prong outlet now ties in to Tom's upgraded halogen headlight harness. Then, the harness takes over and powers the headlights. The TB headlight harness does have to red wires that tie directly to the battery in addition to the adapter that ties in to the original factory 3 prong harness. So, TB harness has to hots going directly to the battery posts. Then, TB harness ties in to the the original passenger's side 3 prong outlet (I think that is what it is called).

So, this is what I have found...........

The original 3 prong outlet has a red and a green wire. It has a black wire but that is the ground. The red wire has power when I turn on the lights. The green wire ONLY has power when I turn on the high beam/dimmer switch. Also, when I turn on the high beam dimmer switch the red wire no longer has power. Is this normal? Shouldn't they both have power if I hit the dimmer switch?

It's a 1976 Bronco. I can't thank you enough. Any help you can give I'd be greatly appreciative. I'm not very good at reading wiring diagrams.
 

garberz

Bronco Influencer
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Jun 24, 2007
Messages
6,856
Loc.
Conejo Valley, Ca.
........So, this is what I have found...........

The original 3 prong outlet has a red and a green wire. It has a black wire but that is the ground. The red wire has power when I turn on the lights. The green wire ONLY has power when I turn on the high beam/dimmer switch. Also, when I turn on the high beam dimmer switch the red wire no longer has power. Is this normal? Shouldn't they both have power if I hit the dimmer switch?

It's a 1976 Bronco. I can't thank you enough. Any help you can give I'd be greatly appreciative. I'm not very good at reading wiring diagrams.

They way you’re reading it is correct, it’s either low beam or hi beam. Not both when the hi beams are on. Some headlight harnesses have the option to run both hi and low at the same time, but it requires a diode so the lows operate independently. Also a lot of standard halogen housings can not handle the added heat of running both high and low at the same time.

Mark
 

Slowleak

Bronco Guru
Joined
Sep 12, 2013
Messages
3,732
Loc.
Georgia
Thank you so much for the help. I've narrowed down the problem. I think. Okay, the bronco came equipped with the upgraded front halogen headlight harness from Tom's Bronco Parts. Basically, the original factory passenger's side 3 prong outlet now ties in to Tom's upgraded halogen headlight harness. Then, the harness takes over and powers the headlights. The TB headlight harness does have to red wires that tie directly to the battery in addition to the adapter that ties in to the original factory 3 prong harness. So, TB harness has to hots going directly to the battery posts. Then, TB harness ties in to the the original passenger's side 3 prong outlet (I think that is what it is called).



So, this is what I have found...........



The original 3 prong outlet has a red and a green wire. It has a black wire but that is the ground. The red wire has power when I turn on the lights. The green wire ONLY has power when I turn on the high beam/dimmer switch. Also, when I turn on the high beam dimmer switch the red wire no longer has power. Is this normal? Shouldn't they both have power if I hit the dimmer switch?



It's a 1976 Bronco. I can't thank you enough. Any help you can give I'd be greatly appreciative. I'm not very good at reading wiring diagrams.


That’s normal. Either the red wire or the green wire will have power. Not both at the same time.

I have the Toms wiring kit on mine as well. There is an installation video here. https://www.tomsbroncoparts.com/pro...duty-wiring-harness-kit-66-77-ford-bronco-new
b8e15bf6ab54a2c47fc19141efe11431.png
 
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DirtDonk

Contributor
Bronco Guru
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Nov 3, 2003
Messages
47,345
Check both inline fuses in the relay harness.
After verifying they're good, and since you seem to have a volt-meter or test light I would pull the relays out of their sockets and test the wires coming in for power. You should have power to one of the contacts all the time (that's the one from the battery with the Red wires) and one that's only got power when the headlight switch is pulled. Then there's the last one that has power only when the high-beam indicator is on.
If these have power as expected, then it's on to test the relays.

Maybe even before you remove them for testing, smack the relays with something to see if that helps loosen something up inside.
Relays are just fancy switches, and they do fail now and then. If you think the relays are questionable (as opposed to something wonky with the wiring itself) then maybe you can get replacements from Tom's.
Sounds like you're not the original owner so you might not be able to take advantage of any warranty if it's still in force after this time. But even though they are a relatively unfamiliar relay style, they are available locally still.
Sorry I can't remember the part number, but it has been discussed here before so maybe someone can dredge that information up for you, if you can't find it in a search.

Good luck.

Paul
 

Jaxgtc

Sr. Member
Joined
May 2, 2016
Messages
520
Along the lines of Dirtdonk, also check the connector at the battery terminal. I had corrosion once that got into the end of the ring connector on the relay wire and ate the thin wire inside the insulation just enough to interrupt flow only on high beam when it needed more juice.
 

blubuckaroo

Grease Monkey
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Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
Pull out the bulbs and check for power and ground at the bulb sockets.
Squirrels chewed the wires from both sockets on mine on a campout. Fortunately repair pigtails were available at the local NAPA.
 
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TexasDude

Jr. Member
Joined
Dec 1, 2017
Messages
66
Loc.
Dallas
Oddly enough, smacking the relay harness really hard worked. The lights now work, However, when I turn on the high beam/dimmer switch they turn off. Ugh, at least now it will pass inspection. They won't ask me to put on the high beams.
 

DirtDonk

Contributor
Bronco Guru
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Messages
47,345
Well that gets you through the first phase anyway. Do it quickly though, before they decide to stop working five minutes before your testing!

I meant to suggest checking the lamps themselves too, like I think someone else did. This is often a first resort, since bulbs do burn out and often can go undiscovered until the second one goes out leaving you without lights.
It's not common that both low and both high beams are out, but it's happened so can't be ignored.
However, sounds like you've narrowed down the issue to either a connection or the relays themselves.

You can verify the high-beam relay too by swapping the relays for one another. If the highs work then and the lows don't, then the other relay is bad.
But even if the one now works, it's a bet that it's not going to work forever if it's stuck once already.

Paul
 

Jaxgtc

Sr. Member
Joined
May 2, 2016
Messages
520
I suspect you could buy just the relays somewhere. A whole new relay wiring kit is only about $35. Time is money... unless you are having fun.
 

B RON CO

Contributor
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Jun 29, 2016
Messages
2,412
Loc.
Statesville, NC
Hi, maybe by just working on it and pulling the terminals apart and putting them back together cleaned up some corrosion for a better connection . I have terminal cleaner spray, and a small wire brush for cleaning. The female plugs are much harder to clean up. Good luck
 

YNOTBOB2007

Full Member
Joined
Oct 2, 2007
Messages
207
Clean the grounds on the radiator support really well. My lights would go completely off when I depressed the high beam switch and once I cleaned those grounds, the lights worked fine.
 
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