Can't turn off my Brights, 1968 Eldorado

[joeinbcs]

Howdy,
I was searching for a new dimmer switch that I thought was the culprit.
Finally found one, installed it, but there was no change in my problem:  Bright lights stay on all the time, and the indicator stays lit.  Depressing the dimmer switch has no effect.
Is there a relay or something else I should check...?
This car has both Twilight Sentinel and Guidematic.  I suppose there is some issue with the Guidematic...maybe a problem in the electropheumatic relay?
Thanks, for any help with this...Joe

[Scot Minesinger]

Joe,

You have probably guessed that the bright beams are turned on by a short circuit.  Your going to have to find it.  Best place is probably to open the shop manual, trace each possible circuit that could energize the bright beams, and go from there.  The first thing I would start with is the auto headlight dimmer.  My 1970 Cadillac is similar and the auto dimmer seems to be the weak link.  Unfortunately it is difficult to diagnose this problem on this forum.  Hopefully someone else suffered the same problem and can state what caused it and you can go right to it.

[joeinbcs]

Thanks, Scot.  That's what I'm hoping...that somebody has experience with the exact problem I'm having.
Thanks for your suggestion, which I may have to pursue if I don't find someone who knows how to fix this.

Joe

[James Landi]

DO the head light "shades"  close and open on demand?   Are you reporting that the lights stay on with the "front lightdoors" closed, and that the lights never turn off?  If everything is working properly, except that when you turn the lights on the high beams stay on, then I concur with the previous post--the "electronic" eye "controller" is keeping them on.  THere is a "sensitivity" switch that, when turned fully counter-clockwise, should click and turn off the auto dimming function and return the driver high beam controller to the foot switch on the floor. Have you tried that?   DId you locate the "sensitivity ring" on your headlight controller and click it to the off position and then push the foot switch? James

[cadillactim]

Make sure the Guidematic and Twilight Sentinel are turned off. Headlights should be off. Pull headlight knob on and see if the dimmer switch will change Hi and Lo beam. If headlights stay on high or low beam problem is in dimmer switch or power relay is stuck.

If headlights work okay this way, but stay on high beam when Guidematic is turned on then problem is bad photocell in Guidematic.

Tim

[Glen]

It has been so long since I had to do anything with the Guide-Matic I don’t remember the details. 

There is a power relay the controls the high/low beams.  It goes to high beam with the relay de-energized and takes power to make it go to low beam.   If the relay case is not grounded the relay will stay in high beam. 
The relay is mounted on the toe pan just above the dimmer switch, under the carpet. 
It may be possible to pull the connector off the relay and connect it directly to the dimmer switch, but I am not sure about that. 

[joeinbcs]

"Did you locate the "sensitivity ring" on your headlight controller and click it to the off position and then push the foot switch? James"
I've rotated the ring all the way counterclockwise, but it does not click, even with a good amount of pressure. Are they all supposed to click. There's no mention of a click in the FSM? I'm afraid any more pressure will break it.
And, Tim: if the power relay is "stuck", do you have replacements, or know a source?
I'm pretty sure it's not the dimmer switch, as I replaced it one that was tested, and good.
Thanks, Joe

[cadillactim]

Joe

The controller ring does not click, and yes I should have rebuilt relays.

You can unplug the relay and plug the wire connector into the dimmer switch (unplug the other connector). This will eliminate the Automatic feature and give you manual dimming only.

Tim

[joeinbcs]

Thanks, Tim.  Please let me know if you have a rebuilt power relay.
Thanks, Joe

[cadillactim]

Joe

I'm out of town until the 27th. Will check for you when I return.

Tim

[joeinbcs]

Thanks, Tim!