Okay so before buying this I saw the review about the guy who had the fire and dismissed it, figuring it was likely installed improperly or a one in a thousand defect. However upon receiving mine it looks like alls well except the box contains this bizarre label on the outside:
“Please Note: These are positive ground controllers. If grounding is necessary it must be on the positive line. If the controller is to be used on a vehicle which has battery negative on the chassis, loads connected to the controller must not have an electrical connection to the vehicle body.”
Now I’m not sure what to make of that but I have extensive electronics and 12v automotive installation experience professionally and this sounds like they designed this device very poorly for its intended application. What it seems they are saying is “do not attach any additional grounding to the unit because its ground scheme is opposite of everything you’ll ever hook up to it and every vehicle made”.
It’s got a plastic case but a metal back panel with 4 screws in it. Removing the back reveals the screws go into just the plastic of the case, so the metal back and screws are electrically isolated from the unit’s internal circuit board and terminals. There are 3 power transistors which use that metal back plate as a heat sink but they are electrically insulated from it with non conductive pads. (the back plate is steel, should be aluminum if its purpose is a heat sink)
So in theory it should still be usable on 12v negative ground systems (virtually every car made since grandpa was born) provided the consumer does not open the case, decipher the circuit board to ascertain its positive ground path points, solder a wire to one and ground it to the vehicle.
NOW WHO IN THEIR RIGHT MIND WOULD DO THAT?
It should still function in a negative ground circuit as long as this device “floats” and doesn’t require a connection to the vehicle other than some nylon plastic cable ties or screws that only touch its plastic case.
So I’m going to take a shot and keep it and install it and update the review as needed.
This may just be a case of an okay product that someone added a useless or confusing label to.
(there is an additional “dear customer” label on the unit itself that is even MORE confusing regarding polarity. Since it seems to concern cables for other renogy products I won’t bother with it)
FURTHER confusion is added by the instruction in the install paper to not let bare wires touch the “metal casing”. Well the casing is plastic and if you didn’t know that you would be scared to screw it to the vehicle.
What I’ll do is hook up a 12v battery, a wall wart with around 18v to simulate a solar panel, and a 12 volt load, with all three electrically attached via negative ground scheme, and we’ll see what happens.
If it burns it goes back. If it works I would advise the manufacturer to get their act together and clean up the labelling to a simple, concise set of instructions that don’t leave even an experienced person scratching their head wondering “WTF is this?”

I used the Renogy 10A controller for the solar charging function of the 70AH / 12V portable power system i recently built. The Renogy controller, along with the Renogy 100W Monocrystalline Bendable solar panel, function very well together and produce the specified charging current into the paralleled 35AH 12V AGM-type batteries.

Working well with my 50 watt panel, also Renogy. Have 5 amp fuse connecting panel to controller and 10 amp to the battery (using 10 awg). 1 star off due to having difficulty tightening the screws. But is working great so far.