Help!...Headlights Always ON....

[GM_Guy]

Did any wires get knocked around or pulled on up front when you pulled the battery? Since the battery junction box is right there, a wire may be tweaked.

Just for the heck of it, smack the lcm with your palm and see if everything starts behaving again.


Alex.

[Galaxieman]

Did any wires get knocked around or pulled on up front when you pulled the battery? Since the battery junction box is right there, a wire may be tweaked.

Just for the heck of it, smack the lcm with your palm and see if everything starts behaving again.


Alex.

When I changed the battery I did have to 'stretch' the battery ground wires slightly to get out of the way. I also have reremoved the battery to look for anything suspicious. The 'large' fuse box is right behind the battery. Will look again...

I have 'smacked' ( actually tapped with a small hammer ) the LCM to no avail...

[Galaxieman]

Update...in the light of day...

Ignition OFF:

Headlight Switch does nothing at all...no head or parking lights
High Beams only come on when flashing momentary ... full on does not work (this may be normal?)
Brake Lights operate normally

Ignition ON:

Headlights ALWAYS ON. Cannot turn off
High beams do work normally both full on and momentary
Turn Signals: cornering light comes on both sides but no turn signals front or back
Brake Lights operate normally

Emergency Flashers never work

Interior lights never work

[Galaxieman]

Another Update...

Cleaned all chassis ground connections near battery. No change in symptoms.

Removed headlight switch to continuity test.

BTW, I started the car with the headlight switch removed...all the symptoms are the same!

DOES ANYONE HAVE or KNOW WHERE I might find HEADLIGHT switch pinout and testing procedure FOR 1999?

I have the 1997 wiring and schematics book but the pinout does not look exactly like my 1999 switch.

Thanks...

[sly]

sounds like the LCM. all flasher logic and timing is there. I have a 2000 EVTM I'll look in. should be the same headlight switch.

[sly]

pinout: http://www.grandmarq.net/sly/2000_CV...ght_Switch.pdf
testing: http://www.grandmarq.net/sly/2000_CV...ch_testing.pdf

[Galaxieman]

Thanks SLY I will check it out...

[Galaxieman]

Well we are making some progress here....Not an hour ago I was sure I had it figured out....not so sure now, but here is what I know:

After doing some tests and studying the schematics, I think I understand what has failed....

Please check my logic here:

The LCM directly drives the low beam headlights.

The LCM is the ONLY source of low beam headlight activation.

The LCM only has ONE input that requests low beam lights to turn ON. That input is directly from the headlight switch (a 12v signal when switch is on).

I removed the headlight switch so that the LCM cannot be getting a low beam request. The low beams still turn on!

Therefore, the LCM MUST be toasted.....right?

Well not so fast....A nice guy sent me the test procedure for the headlight switch. I tested...then I tested again. It appears the headlight switch is also toasted!

I can understand the LCM being toasted from changing the battery but the headlight switch too?

Still a little confused...

[sly]

If the LCM died, it can take anything connected to it down with it. Kinda like the ECM in my 88 dumping the big capacitor in it and nuking the TFI module in the process.

[gadget73]

Do these have automatic headlamps? Nothing as simple as something laying on top of the sensor is it ?

[Galaxieman]

Do these have automatic headlamps? Nothing as simple as something laying on top of the sensor is it ?

No auto headlamps....

[Galaxieman]

REPAIRED!

My Grand Marquis now has fully functional lights!

Here is what I learned:

1. The Lighting Control Module was toasted. Found a used 1999 LCM on eBay, installed it and all lights work fine.

2. I previously reported that I had tested the headlight switch and found it to be defective. WRONG! I had tested the headlight switch per Fords EVTM for 1999. The manual is WRONG. Instructions say to use an ohmmeter or continuity tester and look for 'open circuit' or 'closed circuit'. No matter how I tested it, I never got a 'closed circuit' indication when headlight switch was ON. So, I bought a new switch...it tested exactly the same! It turns out that what Ford means by 'closed circuit' is actually 471 ohms....not a short circuit as you would expect from a switch. The schematic that is with the EVTM test procedure does NOT show a resistor in line with the switch. So now I have spare new switch and new disbelief in the accuracy of ETVMs.

3. I still don't understand how changing a battery could fry the LCM. Should we be unplugging (not easy to do) the LCM before changing the battery?

4. I am going to take my old toasted LCM and have it repaired ($45) and keep it for a spare when this happens again!

Thanks everyone for your suggestions and help.

Galaxieman

[sly]

If the battery terminals get a reverse battery condition, for even an instant, it can fry stuff like that. Also, low voltage conditions can create weird issues for very fast switching on/off and cause metal fatigue on the chips in the module and that can fry them too. I see this at work a lot as I deal with automotive products at the Silicon level.