When I dated a girl I worked with in the late 70's, on our first date we went to see the premier of Star Wars in Santa Ana. As we stood in line outside waiting, we saw smoke coming from a Cadillac in the parking lot. Soon the car was blazing, flames everywhere, the police and fire dept showed up. By the time we got out of the movie, all that was left was a blackened hulk, gutted, sitting on the bare wheels, over melted asphalt. It's not pretty, don't wire into the electrical system.
The way the instructions say to do it is: open the hood, and using the coil of wire, connect the wire with the fuse to the positive terminal of the battery. Connect the ground wire to a ground in the engine compartment. They recommend running the wire from the back, through the vehicle under the carpet, through the firewall, and connecting to the battery/ground. I installed one lift, an outside trunk lift on my first Astro van. I followed the instructions except instead of running the power harness through the van and firewall I ran it under the van, from the battery, down along the frame on the drivers side up high wiretied to the fuel line. Thinking if the fuel line is protected by the frame, so is the power harness. I turned left at the rear crossmember, running the harness across the van inside the crossmember, and then back on the frame passenger side to the rear bumper. I wound the wires around the bumper mount and then up behind the bumper and through the corner of the door so it was inside the van where I wiretied it leaving the end long enough to go back out the door to connect to the lift when I used it. I used it like this for two years or so with no problems.
All the lifts, are wired pretty much the same. But some, those inside the vehicle have to be run under the carpet and through the fiorewall, those outside can be run along the frame as I did. Just make sure however you do it, the wires are protected, up where the won't be damaged, wrap a short piece of rubber or hose around where there're sharp corners or metal, and they may be damaged or shorted. Use lots of wire ties to hold them in place as needed, wire ties are cheap, cheaper than a new lift or car.
Good luck, any questions ask and if I know the answer I'll get back to you.