Joe Parrie,
What an interesting post. I wonder if the heater came stock with the truck or was added by the dealer or a previous owner after delivery.
If you what you describe is true, there must be some connection between heater wiring and ignition wiring...as Oldcarandtrucknut pointed out.
What's interesting is that the run-on time is affected by the heater motor speed. The more voltage applied to the heater motor, the longer the engine runs.
This must mean the connection, whatever it is, in on the load side of the fan speed switch. Does this truck have a new alternator that may have been added recently?
Can you cause this run-on by switching the headlights or any other device on. Although the ignition switch is a common junction for both heater (ACC) and ignition, the fact the the run-on time changes with fan speed sort of precludes the switch from the list of causes....I think!
I have a picture of a fuse block, and the fuse for the heater is adjacent to a pair of pass through terminals for the igniton. Again, these are on the line, or supply side of the fan speed switch, so it still doesn't make sense this could be the culprit. Be sure to keep us posted and maybe someone will pop in with a real deal.
Stuart
