My 94 LT1 in a 75 Vette has been running hot. I think the temp sensor was bad, causing the head to warp. As a backup, I'm thinking of also putting in a temp switch in the passenger head, which would activate the fans if the computer doesnt. As these are both grounds for the relays to turn on the fans, I was thinking of splicing them together. Any thoughts?

 

So you have a warped head, and are chasing an overheating issue?

 

Correct, after the head gasket failed, I removed the heads and had them checked, the mechanic said that one side had warped about 12 thousands and had them resurfaced. They only had 1000 miles on them.

 

Ah ok, thought it was currently warped.

if you splice the signal ground leads together you will always have both fans on. No matter what, so, you take a step backwards as far as OEM setup goes.

If you can find a way to have the two signal leads triggered both off the aftermarket sensor but not backfeed when the PCM triggers the one on, that would be best IMO.