Topic: Lucas fog lights come on with headlights

[Murf]

One night at the Woodward Dream Cruise someone pointed out to me that my Lucas fog lights were on.  They have a tattle tale little hole in the covers and can be noticed by another person but not easily noticed while driving the car.  The switch will turn the lights on and off without the headlights on, but will not control the lights when the headlight switch is on or even just the parking lights lit.  I have been unable to locate a print of this circuit that is readable, but I think that the California Special used the same circuit as the regular GT 68 Mustang.  For some reason the electrical diagram for this option is not common. I changed the headlight switch some time ago but no wires were moved from the plastic plug - the new switch was "plug and play".  Has anyone run into this  problem?  Scratching my head! When the headlights are off and the fog lights activated, the rear lights come on as they should.

[stangfan]

I have a 68 California Special.  My fog lights will operate with or without the headlights or parking lights being on.   They work independent of the other lights.  Is it possible that someone has changed your wiring?   

[Murf]

My Lucas lamps work independently of any other lights, just as yours do.  The problem starts when the headlights are turned on - the Lucas lights come on as well, and they stay on as long as the parking lights or the headlights are on.  The fog light switch has no effect on the Lucas lights when the headlight switch is activated and the Lucas lights stay on until the light switch is pushed to the OFF position.  I have never changed any of the wires and they are configured as they came with the car. 

[midlife]

A common trick is to tie the parking lights into the running lights line at the headlight switch, such that the parking lights are on in both headlight switch pull detents.  There can be a feedback from the parking lights into the foglamp switch if the switch itself is bad. 

Two problems are needed for this to happen...or a bad ground.

Hell, when all else fails, blame the ground!

[67gtasanjose]

Hell, when all else fails, blame the ground!

I've been known to do this

I have never changed any of the wires and they are configured as they came with the car. 

Maybe you personally didn't, but Randy's ideas makes good sense.

I would first unplug the 3-wire FOG switch and try it out to see if the FOG lights come on that way. If the problem went away, I would probably next  check the 3-wire connector for the Fog light switch (harness side) and find the 12v+ power with the headlights and/or running lights on, and after finding the correct pin, turn OFF the headlight switch and provide a 12V+ jumper into that pin. THE HEADLIGHTS SHOULD NOT COME ON, but instead, only the taillights. If the front PARK lights also come on, this too is incorrect. If it works as it should with these tests, just your switch or that Bad Ground.

If the problem DID NOT go away by unplugging the FOG switch, you might wish to check your grounds (that sounds better than asking you to check your shorts )

Hopefully, that should narrow down the playing field a bit.

Richard

[Murf]

Checked the switch this morning. It seems OK to me and the tail light pig tail is NOT connected to the fog light pig tail electrically when the switch is in the off position.  But get this!  while the switch was on the bench, turned on the parking lights and the fog lights came on as well.  Disconnected the tail lights (both sides) at the two plug ins in the trunk and the problem still is with me.  Disconnected left parking light at three pin plug and no change.  Will disconnect the right parking light next just took a little break from this for now.  Any suggestions are welcome.  Anyone have a print of the 68 fog light circuit (seems to be the same as the California Special but not sure of this)  I have Mustang project LED lights in the rear but as noted both side of the tail lights are disconnected. 

[Murf]

Both parking lights have no bulbs, the rear lights are each unplugged, the fog light switch is sitting on the bench.  When the headlight switch is pulled to the parking light position the Lucas lights come on.  They remain on when the headlight switch is pulled all of the way out and the headlights come on.  Any suggestions?

[67gtasanjose]

Maybe try and unplug the headlight harnesses and see what you get then. I suspect that the ground wire is disconnected to the front headights or is dirty.(corroded?)

The circuit sounds identicle to the factory 67 Fog lights I have.

You didn't by chance do anything that may have shorted the wiring harnesses in any way recently? Burned together wiring can be tough to isolate a problem, till you suspect it. (just another possibility. Sometimes we accidently short something thinking it caused no harm, but wires will melt off insulation very fast, even a momentary short can scorch a wire and possibly not blow a main fusable link.(of fuse).

Richard

[67gtasanjose]

Randy @ Midlife, where is the ground wire for the front lamps attached on the 68's? Are the FOG lights grounded at the same location?

Richard

[midlife]

IIRC, the foglamps for RPO systems have their separate grounding ring that is used just for the foglamps.

The Lucas lamps appear to be tied to the parking lamp line rather than the foglamps.  Foglamps are on in both detent positions; the parking lamps only in the first detent position.

[Murf]

Problem solved!  I am writing this wearing a dunce cap- the mistake was mine and made when re-assembling the vehicle.  The Lucas fog lights and the side marker lights (the lights on the side of each fender) are both wired with a connector that has a two wire loom and a male and female idiot proof plug in.  The Lucas lights plug in connector is tinted blue while the marker lights have a brown plug.  You can guess what I did but will confess anyway to plugging the Lucas lights into the side marker circuit and the side markers into the Lucas light feed. 
Took a while to find the problem but was a simple fix once the backwards connection was identified.  Sometimes stupid mistakes happen.. All is well now and you can bet that mistake will not be made again.......Thanks for all of your help!

[ruppstang]

Great John, glad you got it fixed. My dad did the same thing on his 68 GTCS drove me nuts for a while. Sorry I did not remember sooner.
Marty

[TLea]

Problem solved!  I am writing this wearing a dunce cap- the mistake was mine and made when re-assembling the vehicle.  The Lucas fog lights and the side marker lights (the lights on the side of each fender) are both wired with a connector that has a two wire loom and a male and female idiot proof plug in.  The Lucas lights plug in connector is tinted blue while the marker lights have a brown plug.  You can guess what I did but will confess anyway to plugging the Lucas lights into the side marker circuit and the side markers into the Lucas light feed. 
Took a while to find the problem but was a simple fix once the backwards connection was identified.  Sometimes stupid mistakes happen.. All is well now and you can bet that mistake will not be made again.......Thanks for all of your help!

Now that you posted this I remembered once we were judging a car and doing operational check. Noticed during light check owner appeared to be reaching for 2 switches at same time. I went to door and asked him to do it again which is when he confessed he was pulling headlight switch to 1st position trying to manipulate the reesults because they didn't work properly. I told him next time just be honest and we would work with him. I quickly looked up front and saw he did exactly what you did.
ps: did I deduct a point for his improper light control? -1 for trying to fool the judges 

[67gtasanjose]

  I have never changed any of the wires and they are configured as they came with the car.

Ahhhh! I knew there must have been a Mis-leader comment back closer to the original post! It certainly all makes perfect sense now.

lol! Gotta love wiring connections that can be connected incorrectly. I think all responders to this post did "assume" no recent work had been done...we all know the break-down of that word "assume"...still, makes me laugh! Been there, done that on other jobs, sure can be a bear to figure out the "easy answers"

Thanks for letting us know, I had been wondering...