Do not ground the radiator or heater core. Back in the late 90's, I worked at a Chevy dealer. I put 2 heater cores in a Monte Carlo. They would last less than a year. I called GM Technical Assistance and was told to install a ground wire on the core which I did. A week or so later, the Service Manager gets a call from Technical Assistance and they want the customer to bring the car back to remove the ground wire. Apparently, the ground wire is old technology for brass heater cores. I was told to use a volt meter from battery + to the coolant in the radiator. IIRC, .1 of a volt was max. If it was higher than that, it meant that the coolant could be old and acidic or there was a bad ground on the car which was causing current flow through the radiator or heater core. I had to turn on everything on the car to make sure that no component had a bad ground. I actually found corroded grounds at the transmission. It never came back for a leaking heater core. So don't ground an aluminum radiator or heater core.