As with any car old or new we are always hooking up all sorts of new gadgets that need a power source that is a keyed ON.
And we have all seen the creative wiring solutions that can at times be frightening. This article may give you a better and more convenient solution to this power issue.
It really is pretty simple. The main parts needed are as follows:
A heavy duty relay - the one that comes to mind is an early Ford fender mounted style. Your local auto parts dealer should be able to hook you up. The only issue here is that these solenoids were intended for intermittent use, as in starting only. While they do get the job done a better choice is a commercial relay that is specifically designed to for a continuous duty cycle. Grainger(White-Rogers 70-111224-5 rated at 80 amps) is a a good source for this relay.
A terminal block - The screw in style works best for a positive hookup. Get one rated for 30 amps or more. Plan ahead here get one with enough room for future add-ons. Grainger (Grainger Item #6YH66) or your local auto parts store would be a good source here.
The hookup is really simple. The primary and secondary battery hookup is across the solenoid. Just like the starter hookup only now the output goes to the new terminal block. 10 gauge wire would be a good choice here. As with any power system a 30 amp fuse should be adequate. The gnition keyed HOT lead goes to the S terminal on the solenoid. 14/16 gauge wire should be fine here.