Hello, my basic question after searching posts on this site is...how do I test the headlight switch to see if it's bad? More info below if you want to read it.


Thanks.



I have a 79 F-250. Just got it back from body shop due to right front collision damage repair. I still don’t have the right front parking light and side marker light installed yet but both have a bulb in them and are not making any metal to metal contact with anything.

Repair shop said battery went dead and they felt it was faulty voltage regulator so they replaced it. Now my parking lights and side marker lights don’t work. Rear turn signal and brake lights are ok. Headlights work both dim and bright but they flicker. I hear a noise coming from the headlight switch area. It’s an on and off metallic type noise that is in sync with the flickering headlights. I also see the dash voltage gauge moving toward neg when the noise occurs. I’m guessing it might be a built in circuit breaker I hear but the lights only flicker, they don’t go off and then back on.

I checked the ground on the new voltage regulator by attaching another known good ground and no change. I examined the fuses in the panel and all appear ok.

I plan on having the battery checked for any damage.

 

The way you check it is to turn it on... if it works well, it works.

Your assumption of the headlight switch also being a circuit breaker is correct. However, before replacing it (which is the only way to truly "test" the headlight switch is to swap it with another and see if the problem goes away) you need to verify what the voltage is at the battery:

With engine off, no accessories
Engine running, no accessories
Engine running with lights on

Sounds like the voltage regulator and alternator are your problems in my opinion, not the headlight switch.

Josh

 

Well, I put a new headlight switch in and it didn't fix the problem. I also took it to the local auto parts store and they said the voltage reg, altn, and batt are ok. They did find a .26amp draw on the battery with everything turned off. I've been ckecking all my connections (unplugging them, cleaning, tugging on wires etc) and so far nothing. I've been looking for damaged or missing insulation on wires too but nothing. I've disconnected both headlight bulbs and I still get no parking lights (well they faintly blink for a sec then nothing). When I replaced the radiator core support, I painted the replacement. Could this cause a grounding problem? I ran a wire to the neg terminal of the battery and then to the grounding wire attached to the core support but it made no difference.

Thanks for the suggestions.

 

To check for parasitic drain... you start with pulling fuses until you narrow down the circuit that is effecting the system. (Don't forget modern radios with memory)

If the fuses do not make a difference, it is basically narrowed down to the alternator and voltage regulator and to a lesser extent the solenoid.

However, it definately sounds like a ground issue.

Battery NEG straight to engine block.

Ground cable from engine block (or intake manifold) to firewall.

The rest are optional but needed...

A ground from block to frame

Ground from frame to bed.

There are also various grounds behind the dash as well.

I am surprised a little the parts store told you all your stuff check out ok, but that doesn't mean they it right. How did they test all that? With their mobile diagnostic machine?

Josh

 

Have you replaced your dimmer switch?

 

Josh, they did use that hand held machine that prints out a receipt type report. I will do as you suggested on pulling a fuse a t time. I guess it's time I learn how to use my multimeter too.

And highboy, no we have not replaced the dimmer but I tried to clean it. Perhaps I can simply bypass the dimmer to test it.

 

The reason i ask is i had similar problem as yours with my headlights flickering on and off or sometimes just going out completely and having recently replaced my headlight switch i didn't suspect it, it turned out to be my dimmer switch was the culprit, just a thought.

 

Well I got it fixed. I started unplugging the harness (s) and found when I unplugged the left front (headlight, park/marker) harness the problem went away. I then traced it to a positive wire going to the side marker light that had been smashed and was wedged between a bolt head and the radiator core support. I released it from the bolt head, cut out the damaged section and everything is good now. Well, all my connections are clean, got a new headlight switch, and cleaned the dimmer too. Good learning experience.

Thank you all for your help.

Don