I just had a revelation, I recall when I sold Clarks when you dismount the lift you better apply the parking parking 'cause if you didn't that horn will sound when you are about 10' away from the lift & scare the crap out of you. Clark does it this way because OSHA states that the parking brake "shall (must) be applied when the truck is dismounted and the operator is more than 25' feet away from the lift or out of the operator's sight. So this horn activation is tied into the operator presence switch in the bottom portion of the seat and the parking brake actuation mechanism and there must be some sort of switch, like a micro switch, acuated by the P/B foot lever. This assumes the ECG you have has an original OEM seat for electric lifts with a switch in the bottom cushion properly work & connected. Those seat are very expensive and someone may have installed an almost like an OEM seat on the cheap - just a SWAG.