pulsating head lights
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Junior User
Joined: Jun 2009
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From: boones mill,va
pulsating head lights
the headlights on my 79 will start flashing on and off by themselves randomly it doesn't happen often but enough to get annoying. I replaced the headlight switch a while back when it first started doing it but now its doing it again. just wondering if there are any suggestions as to what causes this. I was guessing a bad ground?
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
The headlamp switch has a thermal circut breaker as part of a safety feature.
If there is a problem with the headlamp circut, the circut breaker will trigger, on and off causing the "pulsating". This is so the circut wont get too hot and burn, and so you don't lose your headlamps all at once like a conventional fuse would do.
A Bad headlamp switch will also cause the circut breaker to trigger. (Infact it's the most comon problem, the thermal circut breaker wears out with age.
)
Since you replaced the switch and it still does it, check and/or replace the dimmer switch on the floor. This is also a cause of the circut breaker to trigger. It gets wet on the floor, the connections corrode and causes resistance.
It can also be bad wiring on the truck, or even a defective headlamp switch out of the box.
I'd Check the dimmer switch myself.
If there is a problem with the headlamp circut, the circut breaker will trigger, on and off causing the "pulsating". This is so the circut wont get too hot and burn, and so you don't lose your headlamps all at once like a conventional fuse would do.
A Bad headlamp switch will also cause the circut breaker to trigger. (Infact it's the most comon problem, the thermal circut breaker wears out with age.
)Since you replaced the switch and it still does it, check and/or replace the dimmer switch on the floor. This is also a cause of the circut breaker to trigger. It gets wet on the floor, the connections corrode and causes resistance.
It can also be bad wiring on the truck, or even a defective headlamp switch out of the box.
I'd Check the dimmer switch myself.
Elder User
Joined: Sep 2008
Posts: 563
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From: DeKalb, Ill.
Just another idea. Check all of your grounds. The main one
to be concerned with is your firewall to engine. Make sure that
there is something there, a cable or a braided strap.
This may, or may not fix your problem, but being sure that
this firewall to block ground is in good shape is a good general
place to start.
Murph.
to be concerned with is your firewall to engine. Make sure that
there is something there, a cable or a braided strap.
This may, or may not fix your problem, but being sure that
this firewall to block ground is in good shape is a good general
place to start.
Murph.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
As mentioned before, this is the circuit breaker triggering. If you replaced the headlight switch and it still happens, that means the wiring itself was causing the breaker to trigger. You're going to have to trace the headlight wiring and look for frayed insulation that may be shorting to ground. As 81-F150 mentioned, the dimmer switch is the best place to start.
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Junior User
Joined: Jun 2009
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From: boones mill,va
thanks for the help guys I didn't know there was a breaker in the switch. makes perfect sense now because they flash as if they were on a timer I'll check the dimmer switch
my truck has no floor mat and the pans are rusting out so its very possible rain/water has got to the switch. as a matter of fact it was raining yesterday when they started doing it.
FUNNY STORY
I noticed it when I pulled up behind an small import car that had cut me off just before a stop light changed and caught both of us. I seen my lights flashing in the rear trunk lid of the car and I thought man I bet this guy thinks I wanted to kill him for cutting me off " he keeps flashing his lights at me" the light changed and he sped off and I just laughed turned my lights to park so I wouldn't be flashing any one else. the only reason I had them on is in Virginia you must have the lights on if your wipers are on so luckily I wasn't out on the road in the dark.
my truck has no floor mat and the pans are rusting out so its very possible rain/water has got to the switch. as a matter of fact it was raining yesterday when they started doing it.
FUNNY STORY
I noticed it when I pulled up behind an small import car that had cut me off just before a stop light changed and caught both of us. I seen my lights flashing in the rear trunk lid of the car and I thought man I bet this guy thinks I wanted to kill him for cutting me off " he keeps flashing his lights at me" the light changed and he sped off and I just laughed turned my lights to park so I wouldn't be flashing any one else. the only reason I had them on is in Virginia you must have the lights on if your wipers are on so luckily I wasn't out on the road in the dark.
