Originally Posted by project66
So essentially, both batteries were hooked directly together with a 40 amp fuse between them. Does this fuse give me any protection at all, or should I run this wire directly to the trailer battery (+) terminal as the owners manual shows? Thanks for any help.TomE
The 40 Amp fuse is fine. The most typical arrangement seems to be the tow vehicle battery wired to the trailer battery through a 30 Amp fuse or circuit breaker at each end.
A fuse or circuit breaker at each battery is a good idea so that a short in the charge line either in the tow vehicle or the trailer will not start a fire or do further damage. A 12 V battery will put out a lot
More sophisticated installations use a relay at the tow vehicle end which disconnects the tow vehicle battery from the charge line when the tow vehicle ignition is turned off. That way the trailer cannot accidentally discharge the tow vehicle battery.