37 Ford build--IE: old Header issues thread /37 Ford/5.0/GT40P heads

[Don Shillady]

I have found you can't debug the circuit while connected so I took the unit completely out and have studied it with an ohm meter. I think I have it figured out now but will confirm as soon as it works.

Don Shillady
Retired Scientist/teen rodder

[Don Shillady]

Well, I understand the switch now (Speedway 910-64051) but I must have something wrong in the headlight wiring or a lack of ground for the parking lights. I still have headlights and tail lights when the switch is pulled all the way out but nothing when the switch is pulled half way out. Here is what I found with the ohm meter.

Switch Pull......Battery.....Acc/Park.....Running Lights.....Head Lights
.....0...............+12V...........0...................0.......................0
...1/2..............+12V.......+12V.............+12V.....................0
...Full..............+12V...........0...............+12V..................+12V

Based on these readings I think the tail lights should be connected to the Running Light terminal so the tail lights will be ON for both the Park light option and ON with the headlights.

Then the Parking lights should be connected to the Acc/Park terminal so the Parking Lights will only be on when the pull switch is 1/2 out.

Sad to say this does not work on my setup so I must have some other problem and I will need to check the headlight wiring again. On my currect setup a test light does not follow the same pattern as when the switch is disconnected so I must have a ground loop somewhere or a lack of ground for the Parking Lights. This probably means unwrapping all the wires to the headlight units. This is frustrating to say the least!

Don Shillady
Retired Scientist/teen rodder