I have a 1982 DeVille with Sentinel. I could not get the headlights to work, but the parking lights work as normal. The headlight switch is good and the dimmer switch is good. After looking around again, I discovered that there is a relay or what looks like a relay under the dash about the location just above of where your left foot would be. It is a five pin/wire connector and what looks like a realy connected to it. The dimensions of it are about 2" x 1" x 1-3/8" with a metal cover. The plug has been drawing a lot of current so it has melted some of the plastic in the plug and created loose connections so when you fiddle around with it you can get the headlights to burn, but they only burn on high and the dimmer switch will not bring them down to low beam.
First, what is this relay called because I need to get a replacement and a new pigtail connector. Second, is this normal for the lights to be on high at first, but then what happens to get them to go to low beams. Third, is there another part of the Sentinel system that controls this?
The sentinel feature and the autodim feature, I believe are two seperate features. AT least they are on my 75 Coupe. The question reads as if they are one. Do you infact have both the Twilight Sentinel and Auto Dim features on your car?
After checking, it does have both features. I suppose they are seperate features as you said. How does the Auto Dim feature work? Does it first come on with high beams and then go down? What tell the system the system to dim or not?
Auto high beams, called Guidematic, are controlled by a photosensor behind the radiator grille. The control ring on the headlight switch governs how far away an oncoming light source must be for the high beams to disengage. Twilight Sentinel is controlled by a photocell under the driver's side front radio speaker grille. When this photocell senses an abscence of light, the system activates the exterior and instrument panel lights. The control ring on the headlight switch controls how long the lights will remain on after the ignition is turned off. The two systems operate independently of each other, though they can work together to give you completely automated lighting.
Try operating your lights manually, with just the pull switch on the dash and the foot switch for the high beams. If you cannot get the headlights to work at all or only high beams, check to be sure none of your fuseable links under the hood have melted. If the lights operate normally manually, then one or both of the power relays (for the Twilight Sentinel or Guidematic) has failed and needs to be replaced.
I had this same issue on my 75 after I accidentally shorted the positive side of the battery to ground while changing my starter. FYI don't forget to disconect the battery when working on the starter. Anyway, after tracing wires for a solid day, i found a connector underneath the steering column that part of it actually ran to one of the relays controlling the lights. I was getting power on one side of it but not the other. Not sure why it happened this way but, the connector got slightly melted and burnt the wire. I simply spliced a jumper for that wire to bypass the actual connector. Everything worked like it should after that. GOOD LUCK!! I hope you have an FSM. The schematics were priceless. My FSM is actually on CD and I took the file to Office Depot and they printed it on a sheet of paper that was about 4 feet wide. VERY NICE!!
Any relay gets warm to the touch in operation. A loose, melted connector would raise its temperature even more. If it were mine, I would cut the wires out of the melted connector and solder on female wire connectors to each wire, then retattach them to this relay. You say wiggling this connector restores the lights, so the connector is your problem. Do one wire at a time and reattach so as to put them in order. In order for the auto dimming feature to work, the ring on the headlite switch is rotated to the off position, then engage the high beams. Then turn the ring to the on position. The system should then automatically switch back to low beams. While driving at night, with no steet lights or car lights in front, you will have hi beams. Once it sees car headlights or bright street lights, it will go to dim lights.