Hmm, that’s actually quite ingenious. I guess you’d want to use an SPDT to switch between the regular horn signal when unpowered (ign off) and the VSIM signal when powered (ign on).Couldn't you just wire up an additional relay that's tied to an ignition triggered Aux switch (or simply an ignition source) so that only the horn push VSIM signal is hot to the horn relay when the truck is running?