Headlight dimmer trouble - Vintage Mustang Forums
 
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post #1 of 12 (permalink) Old 07-19-2019, 07:04 AM Thread Starter
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Headlight dimmer trouble

Hey guys. I have a new problem to me on my 66 coupe. Some time after restoring it, the high beam switch stopped working, or at least mostly so. The indicator light stays on all the time when the lights are on, although it doesn’t look as bright as normal. When I press the switch, I can see a very slight change in the headlight strength, but definitely not normal. I replaced the dimmer switch and cleaned the harness connector, but no change. What’s next?

By the way, I had changed the main headlight switch with a nice NOS unit after having the lights flicker on and off. That problem went away, but the dimmer thing came on later, it was not something I noticed right away, and the first few times it happened, it would work after a few presses of the switch, but now doesn’t change at all. It also doesn’t appear that the high beams are on, even though the indicator is lit, so I think I’m stuck on low beam at this time.

Thanks for any advice!
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post #2 of 12 (permalink) Old 07-19-2019, 08:02 AM
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Check the headlight wiring and connectors for corrosion.
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post #3 of 12 (permalink) Old 07-19-2019, 08:10 AM
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If you look at the headlight circuit here it looks like the high beam indicator light is powered off of the same wire (12/34 Green/Black) as the high beams. So since it's staying on you're probably stuck in high beam mode.

My first thought would be that the beam selector switch might be shorting out to the floor or something, but I definitely think it's got to be with the switch or the wiring to it even though you've already worked on it.

You could pull a headlight out and test the connector to see if you're getting power on the high or low beam, or both. But I think ultimately you're going to have to test where you're getting power on the connectors at the switch itself and make sure whether it's actually switching and that it's not grounding out.

Since the headlights come on you know the headlight switch is working so the problem has to be downstream. So it's got to be the dimmer switch, the wiring or a headlight just because there's nothing else in there. It could be a weird headlight shorting out from one filament to the other, or a connector shorting from one to the other but something is putting power on wire 12 when it shouldn't be. There's only the switch, lights, and wires that it could be.

Last edited by Magnus; 07-19-2019 at 08:12 AM.
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post #4 of 12 (permalink) Old 07-19-2019, 08:10 AM Thread Starter
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Originally Posted by awhtx View Post
Check the headlight wiring and connectors for corrosion.
That’s possible, but it’s all new wiring looms and headlights within the last year. I’m starting to think the headlight switch plug may be the key. I’m wondering if the feed wire to the dimmer has worked loose from the plastic plug body. I’m going to pull the instrument bezel to check.
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post #5 of 12 (permalink) Old 07-19-2019, 09:11 AM
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The switch is a mechanically operated push-push, which rotates the contacts. It's probably just stuck. Replace it.

Amateur restorer. Well, sometimes I have been paid for it. But not right now.
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post #6 of 12 (permalink) Old 07-20-2019, 11:04 PM Thread Starter
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The switch is a mechanically operated push-push, which rotates the contacts. It's probably just stuck. Replace it.
That’s the trouble, I DID replace the switch, and it still behaves the same. I’m really thinking the main headlight switch still holds the key. I’ll update once I figure it out. Thanks guys!
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post #7 of 12 (permalink) Old 07-20-2019, 11:09 PM
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It Does sound like a Stuck Dimmer switch...

)

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post #8 of 12 (permalink) Old 07-21-2019, 08:01 AM
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Originally Posted by kellysedars View Post
Iím really thinking the main headlight switch still holds the key.

If any of the headlights work it's not the headlight switch. If you are getting power into the dimmer switch then your problem is in there or in the wiring and connectors downstream.
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post #9 of 12 (permalink) Old 07-21-2019, 08:10 AM
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sounds like a good time to think about installing relays to power the headlights ,It's how they should have been designed from the beginning


Brad
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post #10 of 12 (permalink) Old 07-21-2019, 08:52 AM
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Thatís the trouble, I DID replace the switch, and it still behaves the same. Iím really thinking the main headlight switch still holds the key. Iíll update once I figure it out. Thanks guys!
Strange. The headlight switch has nothing to do with selection of high/low beam. It supplies power to the selector on the floor. Unless a prior owner has rewired the carÖ

Amateur restorer. Well, sometimes I have been paid for it. But not right now.
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post #11 of 12 (permalink) Old 07-21-2019, 09:40 AM Thread Starter
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Yeah, I just wonder if the power feed to the dimmer has worked loose from the main headlight switch, therefore not getting power. I mentioned (I think), that when I changed the light switch with a NOS Ford unit, a few of the female spade connectors were working loose from the plug body, I wonder if a little driving has disconnected the power feed to the dimmer. I guess I could check with a volt meter to confirm, but I’ll likely be pulling the instruments anyway, so may as well check that they are all plugged in.
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post #12 of 12 (permalink) Old 07-21-2019, 10:33 AM
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Did you recheck your headlight grounds?
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