Soon (hopefully) will be installing my Sniper Unit. Holley Rep as well as instructions emphasize direct hook up to battery for power and ground. I am going to run wire from battery to Sniper connection for the power. Not sure about ground. Hard for me to believe a good ground to block or body wouldn't suffice. Having said that if I'm going to run one wire, another would't be any harder. It would eliminate any claim that's my problem IF there are any.
Others may have done it differently, just saying what I'm going to do.
I ran a hot and ground back to the battery on my 65. I also used a bigger sized wire. I ran it down the passenger side under the door sill plates and put it in F6 wire loom. I also ran wires for my Vintage Air.
Holley wants the battery hookup to be directly to the battery. My battery is in the trunk to. When I called Holley the man said that that is the only way they recommend it to be wired. I have a 1/0 cable from the trunk mounted battery to a junction on the passenger side under the dash. He said (from Holley) " I can't say to hook up the pos lead that way.Only that Holley says go direct to the battery. I 'm in the middle of wiring my Sniper now. I ran 10ga. from the front to the back to the battery in the trunk. I'm also using there returnless pump in the stock tank. In the pump wiring they give you a 12ga wire to power the pump going from tank to front. I also changed that to 10 ga.