My tail lights and dash lights quit. All fuses are good. Could it be the headlight switch or a wire going through the frame?

 

There have been reports of problems with the headlight switch on later model Aerostars, affecting both the dash/headlights and dash/tailights. Sounds suspiciously like this may the case with yours. Pull the switch and check also for signs of overheating on the connectors going to the switch. If you see partially melted or softened looking connectors, Ford has a replacement connector for this problem.

 

If you find the problem in the switch, you should consider installing relays to switch the head lights to prevent overheating of the switch in the future. Radio Shack sells these 1 cubic inch 30 amp auotmotive relays, and in-line fuse holders that are almost perfect for this purpose. What IS perfect is a fused relay made by Bosch, also 1 cubic inch, but I can never find them at the same place twice.

I've installed 3 sets of these on my van. There is a vertical panel space near the battery with enough room for installing these. It's close to the battery, so tapping power off of it would be easy. I have one for the low beam because I found my light switch cutting out once just using those. Another is for the high beam, and the third is for the auxillary fog lights I installed.

As someone mentioned before, you would intercept the wires going to the lights to activate the relay, and run power through the switched contacts to the wires going to the lights.