popup headlight trigger from dipped beam

Dualsport, How would this be energized it is a proven constant to momentary set up.  It is an RC Network. The load energizes and then the resistor bleeds off the capacitor causing causing the relay to drop out until power is turned of and on again.

https://www.the12volt.com/relays/page5.asp#ctm

The capacitor allows the coil of the relay to be energized until the capacitor stores a charge, thus de-energizing the coil. The resistor bleeds off the charge of the capacitor when positive voltage is removed from the other side of the coil. You can increase the output time by simply changing the value of the capacitor. This one will give you about a 1/2 second output.