1994 GT Headlight Electrical Problem

[migs_auto]

My son's 1994 Mustang GT has an odd headlight problem that I can now call recurring. Symptom is that his headlights do not come on. He can turn headlights on by pulling towards driver on the turn signal stalk. this however simply activates the temporary high beams. The low beam setting (middle) and the high beam setting (push forward) do not work. I figured it was either the main switch, the multi-function switch, or a relay.

Last weekend we got out the Chiltons manual and since it did not show a relay and since the lights could be activated we figured it was the multi-function switch. We took it out and did a continuity test and found that, in fact, the high and low beam connectors did not have a good connection. He went ahead and took the switch apart (less complicated than I thought) and found just a moderately complicated mechanical switch. The copper parts were all corroded. we cleaned them all off with alchohol, carefully put it back together, and checked it again. Continuity was good for all settings. Probably shoudl have put some dieletric gel before we re-assmebled. Confidently, we re-installed the switch and at first it seemed to NOT work. We disconnected it again and I jumped the two leads in the plug and both hi and low beams worked as expected. We re-installed the switch and now everything worked (a little weird). we patted ourselves on the back and called it a day. Everything was fine for a week and now the problem is back.

I have to believe there is a a relay in between the multifunction switch and the headlights but I haven't found anything that shows thats the case. the Chiltons manual shows a direct connection but it also only shows a generic diagram. there is no relay map that I have found.

Any help is appreciated. In particular, if anyone knows either:

1. Where I can get an accurate electrical diagram for a 1994 GT

or

2. Where I can get a good map of the under dash and under hood relays.

Thanks in advance.

NOTE: Even though the root problem appeared to be in the wiring, I think we did a good thing by taking the multi-switch apart and cleaning it up. It had lots of corrosion. It was moderately complicated and took about an hour to it back together. Still, it was an hour well spent and saved us $$$. It does contain a few small parts so if you are going to work on it, do it over a tray or something so nothing drops on the floor. If your going to buy a new one anyway you don't have much to lose.

[migs_auto]

FOLLOWUP: Took the dash apart again and tested the following:

1. Multi-function switch. All continuity was good.
2. Input from dash switch voltage. 12 Volts as expected. Neither High nor low beams work
3. Input from Temp Hi beam. 12 Volts as expected. Temp Hi beam works.

OK. I tried using a small jumper wire on the plug to the headlight portion of the multi function switch. And got the following results:

1. Jump Dash switch to low beams. No Joy. Huh, this reads 12 volts with no load.
2. Jump Temp hi beam to low beam. It works.

So the line running from the dash switch holds 12 volts with no load but cannot pass any current. When jumped the voltage goes to zero.

We take apart the Main Dash headlight switch and find what appears to be a previous repair that required a whole new plug assembly. Each wire was attached with a crimped connector. The one for the headlights was real hot (to hot to touch). It visually looked OK and after jiggling it, it worked again. I cut it out and replaced with a new crimped connector. This one stayed cool after headlights on for 5 minutes.

I hope this is a good fix. It sounds like this 15 year old car (we own for less than 1 year) had, based on my reading of the forums, a common problem with the headlight wiring. This problem can result in a fried main headlight switch, connector, and some wiring. My problem was that the fix in my sons car also had a problem. Hopefully my fix will last a few years.

[K5Calamity]

Just wanted to say thanks for the info. I know I appreciate it. I've got the same car and although I don't have a problem now, I'm sure I'll be dealing with this at some point.