Thanks again JDL. Here is the final solution. There is a red wire going into the relay that bypasses the resistor block. This wire is always hot. When the switch is thrown into the highest speed the relay kicks in and 12 volts is connected to the blower motor through the red wire going into the relay and the purple wire coming out. The red wire got hot at the connection inside the relay burning up the relay and the plug. That connection takes a lot of current running the blower motor at high speed. I changed the relay and was getting 12 volts into it but coming out of the plug I had nothing. The plug was toasted also. Those two things - the relay and the connector attaching to it were both bad.
I went to a junk yard and they gave me the assembly with three relays the GM says you have to change together. I paid $15. All three relays are the same. The reason GM says you have to change them together is because it is physically very difficult to remove one and put the another one in. When the blower motor won't shut off in an S-10 even when you turn the engine off the contacts in that relay are stuck in the energized position. It is possible to change one relay, so now I have two spares. I made a second trip to the junk yard and they gave me the plug for free. The resistor block has nothing to do with either symptom I experienced. A word of advice to anyone who has a Chevy S-10 blower motor that runs in high speed all the time, even when the engine is shut down and all switches are in off or low position - this is caused by the relay. Usually, you will lose the highest of four speeds in the blower motor first. In some cases you will see this second symptom if the contacts in the relay get welded together and the relay won't kick out. Take the connector off the relay and give it and the relay a good visual inspection.
I plan to change my relay every 100,000 miles with one of my two spares. :)
Friday, July 30th, 2010 AT 12:47 PM