Nah, you ain't matey. Tap in anywhere for your feed to trigger the relay, it only by it's nature needs a very small current, the important bit is the good, (fused) live feed to power your spots. Easiest way, though not nessacelery (!) the neatest is straight from the battery..............er, you don't got an airbox going spare do you? Even a part number might be help?
Best,
Marcus.