Try cycling your dimmer switch several times before you spend bucks on parts.
Howard

I actually had both headlights burn out at the same time. What I think happened was that one of the old headlight bulbs died of natural causes and the resulting current surge available to the other bulb took it out. I replaced both bulbs and everything worked. Nothing more mysterious than two old weak headlight bulbs. 

That happened to me one night on the way home from a car show. Hit a bump and the lights blinked out, actually hit a railroad track bump pretty hard. Turned out to be the plug under the hood right beside the master cylinder. Plugged it back up, good to go.
 

Thank you. Followed the suggestions.This is what happened.

Lights came on when I pressed the high beam switch but went out after a few seconds. Repeated this process several times with same result.   These are standard bulb headlights.  I didn't think that the relay setup was necessary with standard bulbs. Sounds like a switch issue (which is also brand new).  Anyone sell a good quality switch or should I upgrade to the relays and halogen set up?  If I go with the relays, will I need to replace the switch too based on its behavior?

Novi Rick wrote:

Thank you. Followed the suggestions.This is what happened.

Lights came on when I pressed the high beam switch but went out after a few seconds. Repeated this process several times with same result.   These are standard bulb headlights.  I didn't think that the relay setup was necessary with standard bulbs. Sounds like a switch issue (which is also brand new).  Anyone sell a good quality switch or should I upgrade to the relays and halogen set up?  If I go with the relays, will I need to replace the switch too based on its behavior?

Relays are only necessary if upgrading from standard bulbs to halogens or any other type of bulb other than standard.

If you do alot of night driving, i do recommend for safety sake, to upgrade to halogens, since standard bulbs aren't as bright to me. Then you would need relays.

I'm not a hundred percent convinced that its your headlight switch but it does sound like something is tripping.  I would still check the wiring under that high beam switch and make sure its not shorting out under there.

I have heard that the aftermarket headlight switches are sub par, and to  only get a ford replacement part.

I'd go w/the headlight switch.  The contacts get old and may be causing a high resistance contact, the current draw can cause the contact to fully 'open' and the lights will go out.  Exercising the switch can 'clean' the contact to allow functionality for a short time, sometimes longer than others.  However, the only way to truely solve poor contacts is the replace the switch.
Also, the circuit breaker could also be defective ... the circuit breaker is intergal to the switch, so a new switch will include a new CB.
You can try installing relays as the relay coil draws less current than the headlights (standard or Holagens) and therefore the switch may be able to function properly due to this less current draw.
BTW - I suggest upgrading to relays to eliminate the headlight current draw going through the headswitch.

Did you ceck that firewall plug?  Sounds like front half of harness is not making contact.

Rick is this the car volt meter reading 18 volts? Do you have a portable volt meter to double check this reading. If it is actually 18 volts when the car is running this could be your head light problem. Higher voltage will cause lights to draw more current, tripping the circuit breaker. The higher current draw will also burn out your lights. Did you try your lights with the car not running when voltage is closer to 12 volts. The higher voltage and current draw could also damage the turn signals. The turn signal flasher is just a basic circuit breaker that trips and resets itself. But first verify that 18 volt is a correct reading.

Headlight problem
For Mustang Steve - Checked the wiring connection at the fire wall.  It seems tight.

With the car not running, I put headlights on - they stayed lit for about 20-30 seconds and then went off.  With the switch still on, the headlights cycled on and off on their own.  Heard a faint but definite click in the interior.  From what has been described, sounds like it may be a thermal overload going off and on.

Replace switch or go the relay route? or both?

Voltage problem
Checked voltage at the battery with the car not running.  Volts measured 12.7v

Started car - volts reading was all over the place.  Ranging from about 14.4v to as high as 17.8v but it was all over the place.  Revved the engine to a higher RPM (because at idle it is pretty lopey) to see if that made a difference and the voltage reading was again all over the place 14.4 to 17 or 18v.  Voltage was very jumpy which matches what my voltage gauge was exhibiting (and has been but I was too ignorant to address the problem).

So do I have a alternator issue or regulator issue or both?

Thanks for your help!

What are you running for a ground from battery negative to frame and what type of ground strap do you have from the engine to the frame.  Sounds like a regulator but could be either.  Does your local parts store have an alternator tester?  A strange ground could cause similar symptoms.

I would disconnect both front headlights and see if your thermal switch cycles.  If it doesn't it would tell you that you probably don't have a wire short.  I'm not sure what wire kit you used but it is possible that your three poles are not wired properly.  With a voltmeter, verify the negative terminal to low beam terminal and that plus is plus and that only the low beam circuit is active.  Then switch to high beam and repeat.  Check both sides as one side out of whack can affect the entire circuit.  Then I would plug in one headlight and see if that causes your thermal cutout to cycle on low and then high.  Then, unplug the first and try the same with the second.  If they work individually, go for both and see if the problem returns.  I would also check your negative headlight lead to see where it is ultimately grounded.

These seem like basic checks but I usually solve things through a somewhat educated process of elimination.  If I know what is right I can start to narrow down what is wrong.

Step 1 - Check ground on regulator - this is a core support mounted regulator and the ground is through the mounting flange/screw right?

Step 2 - Check grounding strap from engine to firewall.

Step 3 - Check ground for headlight wiring harness on core support.

Guess I will be scuffing some paint to make sure I have a good connection.  Will report back when I get a chance to get this done - hopefully tonight.

some places like autozone will check it for free.