[cletus284]

Neither fan will turn on if I unplug the harness at the temp sensor in the water pump.

That's a problem. Just to verify, you unhooked it while the engine was running and left it that way for 10 seconds or more?

 

[cletus284]

Have you checked the local auto parts store. Dealer is going to rob you!

Here's what I found at Autozone.

http://www.autozone.com/autozone/ca...rCap&fromWhere=&searchText=&_requestid=423249

http://www.autozone.com/autozone/ca...&navValue=15900135&itemId=135-0&parentId=59-0

That is the wrong unit, that's the sender for the guage. This is the ECT sensor: http://www.autozone.com/autozone/ca...&navValue=15900113&itemId=113-0&parentId=59-0

As for the cap, be wary of parts store replacements. I bought one at O'Reilly and took it back because the threads fit loosely and it would pop loose instead of tighten down. Your best bet is to buy an AC Delco one from somewhere, like RMS: http://www.rmsautoparts.com/proddetail.php?prod=RC87

 

[cletus284]

The cap is your best bet.