[kevin69]

I have a 1969 Mach 1 build I finished earlier this year. Although I rarely drive it at night, I recently had to use the headlights and found they don't work! They used to work. When I completed the build the headlights worked though on it's maiden voyage, the lights did go out and come back on a couple of times. In fact, they did the same thing when I was later adjusting their aim. However, they subsequently worked ok, though a short drive. Now the headlights seem completely dead. However, the rest of the lights still work...tailights, side marker lights but headlights (low or high) don't work, nor do the front turn signals which in my 1969 3-wire configuration I believe they also operate as parking lights. From what I've read, the normal culprit given these conditions is the headlight switch (and the high beam indicator quit working too). I tried to debug it tonight but I don't have a good sample to compare or a diagram to determine how to benchtest a switch. The following is what I found:

- This is a replacement repro switch, so it is clean but not a Ford part.
- I found the switch had the following terminals: B, A, R, I, P, H, D1, D2
- With the ignition switch off, I found 12V at B, D1, and D2
- With the switch powered and pulled out to the "headlights on" position, I found the rheostat got very hot to the touch quickly
- After pulling the switch, I found:
o headlights off: there is continuity between B and A, as well as, R and I
o parking lights on: there is continuity between B and A, B and P, and B and I
o headlights on: there is continuity between B and A, B and H, and B and I

I assume I need a new switch but would be interested in any feedback you might have. Thanks in advance!

 

[awhtx]

Did you install new wiring in the car? The light switch has an internal circuit breaker and if the wiring is old and corroded the increased resistance trips the breaker. If you installed halogen lights the extra power they use can trip the breaker. The common cure is to install relays in the headlight system so that the switch only has to power the relays and not the lights. If you feel electrically challenged you can buy a premade plug-and-play headlight harness.

 

[kevin69]

Did you install new wiring in the car? The light switch has an internal circuit breaker and if the wiring is old and corroded the increased resistance trips the breaker. If you installed halogen lights the extra power they use can trip the breaker. The common cure is to install relays in the headlight system so that the switch only has to power the relays and not the lights. If you feel electrically
challenged you can buy a premade plug-and-play headlight harness.

All new wiring and factory headlights.

 

[awhtx]

Power from the headlight switch goes to the dimmer switch on the floor. Remove the connector from the dimmer switch and see if you have power there with the light switch ON. There are 3 wires at the dimmer switch- power in from the light switch, power out to low beam and power out to high beam.

 

[Mach1 Driver]

This may help- it is a schematic, not a wire diagram. Schematics are intended to show you how it works, while wire diagrams show you how it is wired.
The headlights are in the top middle and its about as simple as you can get:

 

[kevin69]

Power from the headlight switch goes to the dimmer switch on the floor. Remove the connector from the dimmer switch and see if you have power there with the light switch ON. There are 3 wires at the dimmer switch- power in from the light switch, power out to low beam and power out to high beam.

Thanks everyone for the suggestions. The one quoted here, however, is the winner! Once I pulled the carpet back to check the dimmer switch, I found the plug to the dimmer had come loose. It was as simple as plugging it back in...and then re-assembling the switch, headlight, etc etc torn down during debug. Both sets of headlights, the front parking/driving lights, and the high beam indicator all work again. Thank you!

 

[Dave R.]

Thanks everyone for the suggestions. The one quoted here, however, is the winner! Once I pulled the carpet back to check the dimmer switch, I found the plug to the dimmer had come loose. It was as simple as plugging it back in...and then re-assembling the switch, headlight, etc etc torn down during debug. Both sets of headlights, the front parking/driving lights, and the high beam indicator all work again. Thank you!

These guys are tuff. Dave R.