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1975 fleetwood headlights not working...

Started by Rdtreur, May 03, 2019, 05:02:52 AM

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Rdtreur

So last night I noticed that my headlights did not work.... I thought a bad dimmer switch but That’s not the problem.
I did some testing and found out that:
- I got power to the blue wire at the dimmer switch, when no headlights are conneted.
- as soon as i connect a headlight to the switch, voltage drops to 0.

Now my question:
- is this a bad wirring problem or a bad headlight switch? Or something else?
- is there a way to do more testing?

It’s got the twilight and auto-dimmer
Many Thanks , Ramon Treur
R.D. Treur
Past caddy’s:
‘68 convertible ‘70 Eldorado,  ‘75 sedan, ‘75 Fleetwood

Cadillac Fleetwood

Ramon,
Start by turning off both the Twilight Sentinel and the Guide-Matic. Rotate the toggles past the detents.  Operate the light switch manually. Taillamps, parking lamps, and side marker lamps will operate in the first position.  In the second, outermost position, the headlamps should illuminate. Operate the dimmer switch. The headlamps should alternate between high and low beams.

You can also bypass the Guide-Matic system.  Lift the carpeting near the dimmer switch.  Disconnect both the three-way connector and the single connector from the dimmer switch. Unplug the three-way connector from the power relay (mounted to the toe-board nearby) and plug it into the dimmer switch. This is the standard "non-guide-matic" wire harness. Operate the lighting switch and dimmer switch again, and check for proper operation.

Charles Fares
Forty-Five Years of Continuous Cadillac Ownership
1970 Fleetwood Brougham
1969 DeVille Convertible
1989 Fleetwood

"The splendor of the most special occasion is rivaled only by the pleasure of journeying there in a Cadillac"

bcroe

Sounds like your 12V is feeding through a high resistance (burned
or corroded) connection, so when the lights are connected, 12V can
not be maintained.  A test light will show where the 12V drops out. 

Bruce Roe

Rdtreur

Thanks bruce, I bench tested the headlamp switch and that worked fine. The problem was in the wire connectors . All the connectors Where a bit heat-worm at the blue wire...
So replaced all the blue wire connectors and the dimmer switch. I think the dimmer switch got worm and caused to much heat stress on the blue wire... not that I am a great electric tech guy, so Please help me if i’m wrong😬
R.D. Treur
Past caddy’s:
‘68 convertible ‘70 Eldorado,  ‘75 sedan, ‘75 Fleetwood