That excellent observation proves the fuses and wiring are ok. Thank you. There are two sets of contacts in the ignition switch; the "run" circuit and the "accessory" circuit. The common contact between them goes to the circuits you mentioned. That common wire can also become overheated causing the same symptom except those items are dead in both switch positions. Since there was a period of time when they worked in the accessory position, it is almost certain the switch is the problem. Regardless, there could be two related problems. Look very closely at the terminals in the switch connector to see if any are discolored or if the plastic connector body is melted. Overheated terminals usually goes along with the overheated switch contacts.
It's very possible the previous defective ignition switch had already led to the terminals in the connector overheating but that part was missed during the repair. Now, if those terminals don't make perfect contact, that adds resistance to the circuit. Current going through that resistance makes heat. High current, such as when running the heater fan on high, makes MUCH heat in the connector which can lead to the new switch overheating. It's a vicious circle.
If you find a melted connector, the burned terminals can be cut out and replaced with individual ones, and about four inches of the wire should be replaced too. Copper wire that was overheated will feel real stiff and solder won't adhere to it when splicing in a new terminal.
The best way to avoid a repeat failure is to not use the highest heater fan speeds. I never use the two highest speeds and seldom use the the second speed. At higher speeds you're actually defeating the purpose. That will blow more cold air through the heater core which lowers the temperature. Think of burning your finger on a lit match. You don't slowly move your hand back and forth and say "ouch"; you shake it frantically to lower the temperature. High speeds work better when trying to blow warm air to the back seat. To use or not to use the high speeds, ... It all depends on much you like your mother-in-law!
Wednesday, December 8th, 2010 AT 9:07 PM