Before we got rich (lmao) and bought all the fancy short detector tools we used to take the main feed wire off the starter battery cable post and put a circuit breaker inline from the battery cable to the main feed wire. With the breaker in place, and clicking from the short, you can disconnect wires one at a time till the clicking stops. It's much quicker to disconnect a whole system at a time to find which has the short and then work within that system. Example: pull "BAT" wire off regulator (charging system), feed wire off dimmer switch (head lights), feed wire from amp gauge to headlight switch, hot wire to amp gauge, accessory wires on ignition switch ( heater, radio, etc). With an old car/truck there are just not that many places a short can hide. If the breaker goes nuts from the get-go then you can disconnect all the systems and then hook back up one at a time till the breaker starts clicking. A circuit breaker runs under ten bucks for 12v but not sure about 6v.