I have an 83 Conquista, and the high spped setting for the blower for heat and A/C stopped working. I thought the problem was the relay, which I replaced, but problem still exists. Any suggestions, I miss my A/C!!

P.S.
Low, med-low, med-high still all work fine...

had the same problem. replaced switch,relay and resister no help. look for a red wire under the hood near the relay or fan. trace it back to the connection.
take a test light tip and push all the wires into the connector and check to see if its clean. I did this and it now works ok

http://elcaminocentral.com/article-9-thread-1-1.html

There's another potential that you might want to check out. The blower speed selector switch itself is sanwiched between copper contacts that can be seen after removing the control panel, bezel, knobs, etc. Sometimes those copper contacts become burned due to a loose condition. When that happens, use some crocus cloth or very fine sand paper to restore the burned surfaces to a shiny condition. If this is the case, you must find some way to permanently squeeze the copper contacts together so they do not burn again. Loose electrical connections cause arcing and that destroys the good connection.

Either the fan resistor or the plug at the resistor is your problem.