My previous coach did not have the +12 charge wire installed to the 7 way. So I ran an AWG12 wire from battery compartment to the 7-way at the back. I went from the chassis battery +, thru a 30A self resetting breaker, thru a 30A relay controlled by a "hot in run" signal from the dash (or maybe it was from the DC power control box). Then in the TOAD, I also put a 30A self resetting breaker near the TOAD battery.
Charge wire from motorhome to toad with the following in series (all other wire in series is also AWG12):
MH chassis batt +
30A Self resetting breaker (in batt compartment)
30A relay controlled by "hot in run" (in batt compartment)
about 30 feet of AWG 12 wire to back of motorhome
7 way socket on back of motorhome (+12V charge pin)
Umbilical (7 wire with AWG 12 or 14 internally)
7 way socket on front of TOAD (+12V charge pin)
30A Self resetting breaker (under hood near batt)
TOAD Chassis batt +
That may be overkill for some. But I don't want to risk a fire at either end, or overloaded the alternator in the event of a short, discharged or damaged battery in the TOAD, or just a heavy load. I even considered also putting in 40A fuses at each end but decided not to. The SR CB's should prevent a fire. And I should notice if they are cycling or there will be obvious other symptoms (toad wont start, clicking, etc.).
I didn't see the need for a manual switch as the Toad battery will not overcharge at the normal run voltage from the motorhome. You may have other reasons though. If you do something like that and add a switch, it could interrupt the "hot in run" relay control and use a low current switch. Otherwise, you would need a heavier switch. I would highly recommend some kind of wiring protection!
Our new coach (to be picked up Monday!) has a relay controlled 12V charge wire installed with 30A fuse on the Freightliner chassis. So Im just going to leave it as is. (per the drawings Freightliner provided)
I cant address the problems of age and installation. You either have to do it or get someone else to. I can still get down under the coach and crawl around. Getting up is the problem!
Oh and I gave the above answer prematurely before I looked at what coach you have. Your 12V charge line to your 7 way is probably also there and also 30A fused. You just need to make sure by checking at the 7 way with a voltmeter. If you want to switch it, you need to find the control wire to your relay and put a SPST switch in line to make the relay open.
The dash cam is a low current accessory and you need to find an always hot and a hot in run fuse to tap off of.
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