This truck came with a dual battery system in place, activated by a solenoid. Pretty typical setup. I've had 2 solenoid systems and didn't like either one, neither would keep the auxilliary battery charged adequately. The PO had a 10ga cable going from the aux battery (pos and neg) back to the rear, into a panel that had a cigarette plug and a voltage meter. He was trying to use it to charge a Jackery battery but it never worked he said, so he put the whole project on hold.
The aux battery was a Yellow Optima, and it was dead. As in 6 volts dead. So I pulled it and got a similar sized lead acid. Lead acid batteries are tough and take harsh treatment and weird charging situations better than either AGM or Li, in my limited experience. But although it would fit the dual battery tray, I couldn't close the hood - it was 2" taller than the Optima.
The winch was wired to the aux Optima, and it was fused - neither of which I wanted. So I moved the winch over to the main battery and fed it directly without fusing it.
So what to do next? I also have 2 x 100w solar panels on the roof rack, cabled down to a switch, and into a charge controller - but nothing downstream from that.
Only the main starting battery is staying under the hood. I moved the lead aux battery to the rear, and am using it to take charge from the solar panels. I'm also using it to feed a previously installed pre-made panel that has 5 individual switched circuits, a pair of USB's, and a cigarette plug, with a voltage meter, in the rear cabinet, but completely unattached to any source or load.
Just wiring things for proof of concept, making sure the solar controller works, that the panels work, etc. The small square panel above the charge controller was fed by that cable from the aux battery originally in the engine bay. I don't think 10ga is adequate size for a nearly 30' circuit run, for a refrigerator, but it would probably have worked. He said he never got good service out of a fridge, this might have been why, not sure. I'm mothballing it for now and will replace it with 4ga if I decide to use it going forward.
Charge controller worked perfectly and I set it for flooded lead acid. Voltage screamed into the battery, plenty of charging capacity for a 90 amp hour battery.
Still need to neaten up some wires but it's basically done for now. Sunk two heavy eye bolts into the plywood floor and secured the battery. The 5 switch panel seen above is going to supply all my accessory loads - so far I wired an interior light on the far right switch and a rear facing rack light next to it. I'm using Iron Man brand rock lights - they're very bright, small, tough, and unobtrusive. And not expensive.
The interior is perfectly lit with one rock light, on the underside of the shelf panel. The rear is attached to the rear bar of the rack - the picture doesn't do it justice at all, it bathes an area about 40' in diameter with really useful light - not too crazy bright, like some "work lights" I've seen.
I think I'm getting things pretty dialed in. I don't know of any other major weaknesses or deficits that need to be corrected. This is why I bought this truck - it was relatively perfect for me from the get-go. I could have spent less on other, maybe nicer, trucks, but then I'd be starting off sourcing bumpers and winches and building interior cabinets and so on, most of which would just never get done because Life Finds A Way (of getting in the way.)
I do want a rear locker- that's probably the only thing. And a bunch of soundproofing and a new interior rubber mat up front. I will change out the headlights for my new Koito kit from VintageTeq but I'm still waiting on the #%@^#&$% rear headlight ring - two false alarms on the right hand side one. The left hand one is available all over the place - they lay on the ground like fallen leaves - but that right hand side one...let me just recommend you get those rear headlight rings while you can in case you need to renew yours.