Headlights

[fyreduck1921]

I have a 76 Bronco Sport and the other night I pulled the headlight switch and ****: both headlights came on for a fraction of a second, then went off. I cycled the switch on and off and nothing. Dash lights work, dome light works, but no headlights. I stepped on the dimmer switch, and the high beams came on. Switched back to low beams and still nothing. Also, with the dimmer switch on Low Beams, the volt meter is bouncing all over the place. Any ideas would be greatly appreciated.

Thanks,

Steve

 

[Bully Bob]

Test lamp blades for continuity ...,   & female plug for voltage.

Might also want to check/test the alternator output.... some times they can "run wild" & over charge.

The headlight switch is a busy unit & may have failed internally. The (exposed) dimmer switch  wires get dirty & a rarely used dimmer switch's contacts get a 'lil corroded over time. 

 

[fyreduck1921]

Thanks for the tips BullyBob. I was in the parts store ordering parts for my 77 F-250 project and picked up a dimmer switch. $7 and 5 minutes later, I had Low-Beams again.

Steve

 

[fyreduck1921]

Ok, so I drove to the parts store tonight, which is all of 2 miles from my house. When I got back in the Bronco to leave...**** the low beams went out again. Same symptoms. When just the parking lights on, or the high beams on, everything is normal. When I attempt to turn on the low beams, they don't work and the voltmeter goes crazy.

Could it be

1. The headlight switch itself?

2. Or do I have a short in a wire somewhere? Do the low beams and high beams have separate power wires coming from the dimmer switch?

Thanks,

Steve

 

[Bully Bob]

"....Do the low beams and high beams have separate power wires coming from the dimmer switch?

Yes.., power (+) comes from the light switch to the dimmer. There's two "out" leads.., one to hi & one to lo beams.

Sounds like the light switch is OK.

"....do I have a short in a wire somewhere?"

This is a possibility. Trace the two (one being the lo beam) fr. the dimmer switch.

These two should run up to (the other half of) the rubber plug under the dash.

Another test would be to "wiggle" the rubber plug on the firewall (under hood). Most all the wiring goes thru that plug & sometimes a connection will get corroded.

I've never un-plugged mine.., the thought worries me.  However, I've not had a loss of power anywhere so

there hasn't been a need to.

Sounds like the ground wires at ea. headlight are OK but you might check & clean them while you're at it.

Keep us posted...,

B

 

[Bully Bob]

I took a quick look at mine.., the hi/lo beam wires run along the driver side fender well, to the driver side

headlight. the same wire leaves there & runs along the rad. support to the pass. side headlight.

Soooo.., the circuit is pretty simple.., from the dash switch, to the dimmer, thru the rubber plug, to the headlights.

NOTE: these wires are wrapped in a group with others. At some point, it may req. un-wrapping to inspect.

 

[fyreduck1921]

Thanks Bullybob for the help. It took about 3 hours but I finally found the problem. The previous owner had installed an aftermarket radio under the dash just below the factory radio. Apparently when he ran the self-tapping screws into the dash, one of them punctured the low-beam power wire, grounding it out. What tipped us off was when we realized that the radio shut off when the low-beams were kicked on.

 

[Bully Bob]

Good job..!!!

Thanks for the feedback.., we rarely hear back from folks as to a problem solved..., or not.

B