There are continuous-duty relays that resemble the Ford starter switches in size and current capacity. Go to a motorhome dealer, and ask for a "battery isolation relay". They look just like a Ford starter switch, but they are intended to operate anytime the engine is running on a motorhome to charge the coach battery. Once the engine is shut off, the relay disconnects the coach battery from the starting battery to keep the engine-start battery from being drained while camping.
Just wire the relay's energize lead to close the relay whenever the ignition switch is in the "on" position, and wire all the heavy current draw circuits through the main contacts. Problem solved! I ran a Freightliner with the same setup on 20 clearance lights, with virtually no current draw across the toggle switch that controlled the relay.
Jerry
