I need electronic guidance...

[snailexpress]

(03-27-2018 )Hammerhead Wrote:  

(03-27-2018 )snailexpress Wrote:  Google battery isolator if you don't want to reinvent wheel.

I thought about an isolator, but I'm just scavenging power from the seventh wire of the trailer cord.
My understanding of an isolator is requires a larger gauge feed wire from the alternator?

Inside in isolator is diodes or field transistor what is exactly what you going to do. You don't need to worry about encasing home brew to protect circuit from weather, how to make studs and on. To protect trailer power supply circuit use headlight bulb in series as Rawze mentioned. Current will not exceed bulb watts/12 v. For example 65 watt high beam bulb will keep charging current 5.5 - 6 amp even in worst case when battery shorted inside. Check the fuse amps installed on the truck. Total current for all consumers (ABS with energized solenoids, strob light, charging battery and whatever else you have should not exceed 60% of the fuse rate. Check wire rate for this current. 2 amp/mmsq for copper is OK for air cooling.