Headlight problems?

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DirtDonk
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Post by DirtDonk » Tue Nov 14, 2017 1:19 am

Wow, no highs all this time, eh? I wonder if after all that it's the new(ish) relay harness?
But before we go down that road let's check some more ground aspects.

The only grounds associated with the headlights are right there behind each headlight into the core support. If you have painted the rig before installing the new harness, or there was any rust in the area under the terminals, you should remove the grounds from the studs, scrape/sand the area underneath, the re-attach the wires. If you're like me and hate future issues like I do, give a quick shot of spray paint over the tight connections. This way the bare metal that counts is in contact with the ring terminals, and any other that shows is now covered by paint. Almost rust-proof.

Next, did you add any grounds to your harness? This means more than just what you would normally have seen on an old Bronco. Of course there is the main battery cable ground from the negative terminal to the engine block. BUT (and this is the one that is left out most often) you also need a good connection directly from the battery to the body. This would usually be a 10ga wire right to the body. Typically the fender well under the starter relay. Use one of it's attaching screws to hold the new ground. Alternately you can use the original hole on the wheel well's inner side facing the exhaust manifold on the passenger side. You'll see a small-ish (1/4" maybe?) hole already punched into the metal.
After you ground the body, run a secondary jumper wire between the new body ground and the core support where the headlight grounds are.
Next add another auxiliary ground between the back of the engine and the firewall.
If you've a mind after all this, add a jumper ground between the engine and the frame, or the body and the frame. Or both. You can do it real clean and tidy down at the motor mount area and most people will hardly notice the extra wires.

I don't really know that this is the issue, or that you haven't done all that already. But it's good to get grounds out of the way first, before pulling your hair out tracking down a problem.

If that doesn't do anything, let's check out the high-beam section of the relay harness. We can talk about that in detail when you get back after the grounding party.
But in the meantime you can verify that your high/low switch on the floor is working. Assume you have a test light or a volt-meter? Check the output of the switch with the lights on. See if it's getting past the switch.

Good luck.
Oh, and sorry it took so long to get to this. I did not get a notification for once. Or if I did I forgot about it.

Paul
'71 Bronco - 302 4v
3.5" WH/Skyjacker Lift
33 x 11.50 x15 Thornbirds on 15x7 Enkei's
Kayline soft top
Hanson bumpers
Dual batteries, Large 1G alt.

WWW.WILDHORSES4X4.COM :mrgreen:

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Puff Daddy
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Post by Puff Daddy » Wed Nov 15, 2017 11:46 am

Thanks for the advice. I've already checked the floor switch by using a jumper cable on the cannon plug. They didn't work even when the switch was isolated. I also replaced the dash headlight switch for good measure. I'll start doing a good cleaning on the grounds.

One thing I don't have that you just mentioned is a ground from the starter relay to the wheel well. I always thought that it was grounded through the base of the relay itself. Let me check all that and I'll get back with you.

Tom
Tom

Uncut '73, stock 302 w/Headers, Holley TA Carb, Centech Harness, Wildhorses 3.5 inch lift.

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Post by DirtDonk » Wed Nov 15, 2017 11:57 am

The relay is indeed grounded through the base. It was the body itself I was worried about. There is always supposed to be an additional ground wire to the body. This gets left out of the equation more often than not, when an owner replaces the original ground wire.

What ford did was use a metal clamp to the body before the cable reached the engine block. What many people don't realize is that this "clamp" is not just for holding the wire in place, but in fact is soldered and/or crimped to the actual conductor to act as the body ground.
So when an aftermarket cable is used, it's up to the installer to add the ground back to the body somehow.
Often you see the ground cables with an additional 10ga pigtail and yellow butt-splice crimped to it's end. That's there for you to extend it to the body.

The problems also come up with headlights because over the years the core support gets less and less contact with the rest of the body and grounding bonds. This seems strange, since it's literally spot-welded to the fender skirts. But 50 years of rust and dirt and dust and layers of light corrosion block the path of electrons so you get a bad connection. Hence the need now, more than ever, to add multiple additional grounding points.
All the OE's including Ford have done that for decades, including while the Broncos were being built still. For some reason they decided to scrimp and save by leaving out some key wiring components that every other passenger car and it's brother did get. Heck, even the later seventies full-size trucks had multiple braided straps just bonding the cabs to the frame, and the body to the hood! Everything got a ground.

If your Bronco can't tolerate AM radio because of too much noise, we can probably thank lack of grounding at least in part.

Paul
'71 Bronco - 302 4v
3.5" WH/Skyjacker Lift
33 x 11.50 x15 Thornbirds on 15x7 Enkei's
Kayline soft top
Hanson bumpers
Dual batteries, Large 1G alt.

WWW.WILDHORSES4X4.COM :mrgreen:

DirtDonk
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Post by DirtDonk » Wed Nov 15, 2017 11:58 am

While you're mucking about in the wiring, swap relays from one to the other. You know the low-beam relay is working, so try swapping it to the high size just to see if the trouble follows. If it does then you have a bad relay. If it doesn't change, then the fault is back in the wiring.
It could actually be in the harness itself.
Either the truck harness, or the headlight relay harness. Just gotta' narrow down the suspects.

Paul
'71 Bronco - 302 4v
3.5" WH/Skyjacker Lift
33 x 11.50 x15 Thornbirds on 15x7 Enkei's
Kayline soft top
Hanson bumpers
Dual batteries, Large 1G alt.

WWW.WILDHORSES4X4.COM :mrgreen:

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Puff Daddy
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Post by Puff Daddy » Mon Nov 20, 2017 6:56 pm

DirtDonk wrote:While you're mucking about in the wiring, swap relays from one to the other. You know the low-beam relay is working, so try swapping it to the high size just to see if the trouble follows. If it does then you have a bad relay. If it doesn't change, then the fault is back in the wiring.
It could actually be in the harness itself.
Either the truck harness, or the headlight relay harness. Just gotta' narrow down the suspects.

Paul
Swapped relays, cleaned grounds with no luck. Before I got into creating extra grounds, I went out and bought a circuit tester...which I should have done in the first place. I started testing the circuits at the plugs using the plug grounds. All the plugs are getting power (using the plug grounds) to include plugs that attach to the light bulbs.

It seems weird to me, that the problem would be the headlamps. I find it unusual that the brights would be burned out at the same time on both headlamps. Is that strange to anybody else?
Tom

Uncut '73, stock 302 w/Headers, Holley TA Carb, Centech Harness, Wildhorses 3.5 inch lift.

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SHAWN
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Post by SHAWN » Mon Nov 20, 2017 7:19 pm

A 'circuit tester' will not put a load on the system... your volt meter may say everything is good, but if you run a load on it, poor connections or an 'open' may pop up as a result an inoperative lamp. If you ohm test the headlamp itself, is there continuity between the terminals of the bulb (when it is NOT plugged in!)? Try back-probing the headlamp connector with everything plugged in. Is this an intermittent problem,, low beams too? the system must be failing while testing for anything to show a fault.

wow, you sure did bring an oldy back up

...Hey Tom, glad to see you back checking this site.
8)

Shawn.
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Post by Puff Daddy » Tue Nov 21, 2017 12:26 am

SHAWN wrote:A 'circuit tester' will not put a load on the system... your volt meter may say everything is good, but if you run a load on it, poor connections or an 'open' may pop up as a result an inoperative lamp. If you ohm test the headlamp itself, is there continuity between the terminals of the bulb (when it is NOT plugged in!)? Try back-probing the headlamp connector with everything plugged in. Is this an intermittent problem,, low beams too? the system must be failing while testing for anything to show a fault.

wow, you sure did bring an oldy back up

...Hey Tom, glad to see you back checking this site.
8)

Shawn.
Thanks for the advice Shawn.

It's a constant problem...been going on for probably a year and a half. I just started tackling it in earnest now. The low beams work fine. I'll check the continuity of the bulbs in the morning.
Tom

Uncut '73, stock 302 w/Headers, Holley TA Carb, Centech Harness, Wildhorses 3.5 inch lift.

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Post by Puff Daddy » Tue Nov 21, 2017 10:41 am

It turns out that the problem was the headlamps. Both brights were burned out. I installed a new lamp on one side just to double check my theory this morning and it was confirmed...it worked just fine. Still not sure how it happened. Thanks for all the input. I still learned a lot about trouble shooting the electrical system.
Tom

Uncut '73, stock 302 w/Headers, Holley TA Carb, Centech Harness, Wildhorses 3.5 inch lift.

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Post by DirtDonk » Sun Dec 03, 2017 12:16 pm

It's not really unheard of. Not common of course, but not impossible. As you found out!
And they may not even have burned out at the same time either. They could have due to some voltage spike or another, but it could have happened to one and you may not have noticed right away. Then the next one went out and of course you would notice at that point no matter how often you used them.

Might even have been due to bouncing around over the years, but normally the filaments are pretty robust to handle all the heat and vibration normally. But you never know.
Are these sealed beams or H4's? New or old? Name brand or cheap copies?
Reason I ask is that a buddy had an H4 conversion and both (or at least one?) of the bulbs was defective right out of the box. I should say right away rather than right out of the box though, as I don't remember if he got any use out of them before failure or not. But new bulbs fixed it.

Glad you found it!

Paul
'71 Bronco - 302 4v
3.5" WH/Skyjacker Lift
33 x 11.50 x15 Thornbirds on 15x7 Enkei's
Kayline soft top
Hanson bumpers
Dual batteries, Large 1G alt.

WWW.WILDHORSES4X4.COM :mrgreen:

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Puff Daddy
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Post by Puff Daddy » Thu Dec 07, 2017 6:18 pm

They were old, and probably the cheapest I could buy 18 years ago, which was the last time I replaced them. (Cracked one in a fender bender. My winch bumper took a beating, but the Pontiac Sunbird was totaled). They're gone now, so I can't tell you for sure. Upgraded to the LEDs...wish I had done it long ago. The difference is literally like night and day.
Tom

Uncut '73, stock 302 w/Headers, Holley TA Carb, Centech Harness, Wildhorses 3.5 inch lift.

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