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1977 Eldorado Headlights won't turn on

Started by joecaristo, August 21, 2020, 01:21:52 PM

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joecaristo

Hi everyone. Has anybody had this problem before? I know to check the plastic connector under the rug. I've replaced the foot switch and the dimmer switch. Still no lights. Anything else in line with the headlights? If not, In the wiring I'll have to see where its losing power. Thanks.
Joe Caristo

TJ Hopland

Simplified not super car specific.....

3 fusible links on the big battery terminal on the starter.    One feeds the fuse box for the stuff that is always on.   One feeds the key which then feeds the rest of the fuse box for the stuff that comes on with the key.   Last one feeds the headlight switch assembly which has its own breaker and such and only feeds the headlights,  running and brake lights are fed from the fuse box but switched by the headlights so that can be confusing. 

Corrosion and damage from changing starters and not carefully watching the wire routing can easily make contact with exhaust and such so a visual check around the starter and of the harness may give some clues if there is a likely issue there.

Does your car have the guidomatic auto dimming?    3 or 4 terminals on the floor dimmer switch?   Guido had 4 and is a more complex system involving some relays.    The non guide system is fairly straight forward and you could try using a jumper wire from some power source in the fuse box to one of the 3 pins in the floor dimmer switch if its a non guide system.   In theory doesn't matter which you try.   One will be the feed from the headlight switch so applying power there should not harm or do anything unless maybe that is where the issue is and there is a short?  So sparks may be possible?    Remaining pins will be high and low beam.

For the testing if you have a spare headlight laying around you could wire that in series.   That would be one wire from your power source to the spare light and then the other terminal on the spare light would be your probe.   If you probe something that is a positive voltage nothing happens.   If you probe something that is shorted to ground or grounded the light will light normal brightness.    IF you probe something like the headlights all the lights should light at around half power.   Kinda a nifty fairly safe cheap way to test things.

If its a guide o mattic you need some specific details like wire colors and pin numbers to start troubleshooting.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

joecaristo

thank you. My car does not have sentinel or Guide matic.
Joe Caristo

TJ Hopland

The should be fairly easy to feed some power into the floor dimmer switch connector and see what happens.  If you can get the lights to light that way you know its a power feed issue either the fusible link or switch assembly.   

If the lights don't light then its a wiring issue between that connector and the lights themselves. 

To know if you got a bad dimmer switch just jump the terminals together.  One combo will be high to low which won't do anything but the other 2 combos should light either high or low assuming the feed was good.   I think a clue to which pin is which is the highbeam has 2 wires on it,  one goes to the lights and the other goes to the dash indicator.    That means the 2 single wires should be the feed and the lows. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

joecaristo

Just wanted to give an update: The Headlight switch connector was burned out at the blue wire in the dash. Replaced the wiring and connector and all is good. Thanks for your response TJ Hopland
Joe Caristo