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Electrical Issue -- Headlights

Oakland Bronco

Sr. Member
Joined
May 13, 2010
Messages
721
Loc.
San Francisco, CA
I discovered that when I take the Bronco out at night, the headlights and running lights seem to work find. Until the Bronco is warmed up. At that point, the headlights and running lights flash on and off intermittently. To be clear, the headlights and running lights turn on and off at the same time.

The person who worked on the electrical believes that the grounding is loose, but it seems to me that the lights would flash on and off as soon as I hit any bumps. The lights are solid with bumps until the engine is warm.

I recently had a new stereo unit put in, and the installer said that the ground wire seemed unusually hot.

Thanks for any thoughts and suggestions you have. Obviously not being able to drive at night is killing me.
 

Viperwolf1

Contributor
electron whisperer
Joined
Aug 23, 2007
Messages
24,316
A hot ground cable is a sign of high resistance. Take it off and clean it up. Replace the cable if it's stiff or the insulation is swollen from corrosion. Fix that first.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
What he said.
But once you've done that, if your lights continue to go on and off at intervals, it's likely your headlight switch is old and needs replacing.
It's either that, or something else in the headlight circuit is drawing too much current and causing the internal circuit-breaker to overload and momentarily break the connection.
Could be aftermarket headlights that are putting out too many watts. Could be something added to the light circuit that shouldn't be. Maybe the radio?
With Broncos having so few open circuits to use for aftermarket stuff, you need to verify where anything you've added on is pulling it's power from. If anything else is hooked to the headlight circuit, you'll probably be better off moving it somewhere else.

It's usually an old switch, but in your case you've got other issues that can do funny things. The ground wire (and all battery cables actually) should not only be in perfect condition, but of sufficient gauge to handle anything you throw at them and then some.

Good luck. Oh, you can test the headlight switch theory by disconnecting one headlight. If it stops doing it, your switch is overloaded Probably from being old.

Paul
 
OP
OP
Oakland Bronco

Oakland Bronco

Sr. Member
Joined
May 13, 2010
Messages
721
Loc.
San Francisco, CA
Issue Resolved

What he said.
But once you've done that, if your lights continue to go on and off at intervals, it's likely your headlight switch is old and needs replacing.
It's either that, or something else in the headlight circuit is drawing too much current and causing the internal circuit-breaker to overload and momentarily break the connection.
Could be aftermarket headlights that are putting out too many watts. Could be something added to the light circuit that shouldn't be. Maybe the radio?
With Broncos having so few open circuits to use for aftermarket stuff, you need to verify where anything you've added on is pulling it's power from. If anything else is hooked to the headlight circuit, you'll probably be better off moving it somewhere else.

It's usually an old switch, but in your case you've got other issues that can do funny things. The ground wire (and all battery cables actually) should not only be in perfect condition, but of sufficient gauge to handle anything you throw at them and then some.

Good luck. Oh, you can test the headlight switch theory by disconnecting one headlight. If it stops doing it, your switch is overloaded Probably from being old.

Paul

You were right about the switch and the current. I had the switch replaced, but the lights only stayed on for about 30 minutes before starting to flash on and off again. A lighting relay solved the problem. Also got new battery cables installed, as they were looking a little worn. Thanks again for your suggestions.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
Great news.
That relay setup is a bonus even if you didn't have a problem with anything else. It's just a good way to run headlights, so that they obtain their full potential.

Paul
 

miikee73

Shadetree Guru
Joined
Dec 14, 2010
Messages
3,551
Loc.
Aloha
Great news.
That relay setup is a bonus even if you didn't have a problem with anything else. It's just a good way to run headlights, so that they obtain their full potential.

Paul

I did the relay mod before any problems came up.I don't think the quality of the light switches you buy today are as good as the original.
Just one more subject I read about on here that enlightened me about the quirks of the Broncos.
 
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