I noticed your question on the bulb out sensor. The replies your getting are correct accept for a small detail or two. One the device does not work on voltage difference. 12 volts is available to all wires equally. It works on current/resistance differences. The device also is not a relay. It has no moving parts. The device does not control a circuit of different voltages or of higher/lower current.

The SENSOR work on the principle of inductance. Current flowing through a wire creates an magnetic field in one direction. Wind one circuit thats wound in one direction against the other side and they cancel each other. Any INDUCTION goes into the third circuit, to the dash light. Bingo, one side goes bad, current(magnetic flux) lights the dash light. Imagine three loops of wire one wound with leads out each end with the third in the middle. Like a TRANSFORMER. 1 to 1 ratio.

Keeping connections clean and bulbs that consume current equally is the ticket.