Hello all new to the platform. I have a 1986 IROC Z28
the cooling fan does not turn on. I replaced the fuse and the relay.

 

What happens when you bypass the relay and temporarily give +12v directly to the fan?

 

The Fan turn on.

 

Ok, so we know the fan is capable of working, that means there's a problem sending the signal to the relay, no ground at the relay, or no 12v for the fan at the relay. Basically, follow and test every wire at the relay and figure out which one isn't doing the thing. Factory service manual is a pretty big help for electrical.

 

The plug for the fan harness (I'm pretty sure, it's been a while) is to the right of the battery standing in front of the car. The black wire on that connector likes to burn up. Unplug it and give it a look over.

 

So i was back at it yesterday. No matter what I do, I can not get the fan to turn on unless I jump the ORANGE / BLACK-RED wires.

These are all new in the car.
Radiator cooling relay
Coolant temperature sensor switch
Coolant temperature sender switch
Idle control valve
Throttle position sensor

 

As discussed you need to test all wires at the relay to see if they are doing what they are supposed to be doing.

Orange is power to the relay - Needs 12v HOT at all times
Black/Red is Power to the fan - Sending 12V to this should turn fan on (as you say youve done)
Brown is Key on Power - Needs 12v with Key on
Dark Green/White (Or whatever color the 4th wire not yet tested is) is the ground wire from ECM that activates the relay - With key on you should be able to ground this wire/terminal and the relay activate the fan assuming all other wires check out