As I stated in my build thread, I connected a battery to test my progress with wiring and components. Two of the things I found wrong:

1. Gauge lights and license plate lights are on all the time (with the battery connected)

2. When I switch on the head lights, they go up and down endlessly.

Any bright (!) ideas? I suspect I may have one or more connections incorrect, or maybe a bad head light switch?

I believe you may be on to something with the headlight switch. I know there are several terminals on them. Maybe one of those terminals once hooked up, is constantly on, a multimeter could answer that fairly easily. I am not looking at a wiring diagram for the car, but maybe those two sets of lights are on the same circuit, then plugged directly to the headlight switch.
As for the headlight motors, is there a limit switch that is not being triggered??
As I write this, maybe these two problems are one in the same, sounds like the headlight motors and the gauges and plate lights are on the line side of the switch…or relay. I am assuming the switch has line and load terminals….as would any relay, speaking as an electrician..