The internet is a really bad place to see how people think certain items work. Ford dome lights in the 60s Ford is high amongst those.
I am in the beginnings of a custom harness for my modified car. Naturally the harness is made around GM design. After looking into Ford and GM circuits it became apparent no one knew how stock Ford (Mustang) dome lights really work.
To that end, here is a highly simplified version of the stock Ford system that I created. All Ford circuit numbers are used without the alpha suffix since the different letters just identify traveler wires.
--The circuit is powered by the Courtesy Light fuse (see your fuse box for where that is located for your year) which routes power to the headlight switch. D1 on the switch is powered by this 12V always on circuit.
--All door switches are N/O (normally open) with the doors shut. The switches are NOT grounded and have two poles which are joined when the doors open. The plunger in the door switches below shows the switches held open by the doors pushing the plunger away from the contacts.
--When either (or both) door(s) opens, circuit 54 powers circuit 53 which powers all lights . The lights are individually grounded.
--D2 is a headlight switch circuit energized when the user turns the pull-knob CCW. The 'green flag' looking item is actually a ramp which when the shaft is turned joins circuit D1 to D2. This energizes circuit 53 and turns on the lights regardless of door switch position. D2 has no other function.
Interestingly, GM runs power to the lights and their headlight switches lead to ground (not a fusebox) as do the door switches.
[Reduce pic size]
