My fan quit working today on the LT4 powered truck with a '95 PCM, even with the AC on and up to op temp.
I popped the relay off and the main power supply pins are labeled 30 and 87.
One is the supply voltage and the other goes to the fan.
Two other wires act as the switch, labeled 85 and 86.
I assume one is the CTS and the other is the AC on command.

What voltage should I be seeing on the switch control wires 85 and 86?
One seems to always be "on" no matter if the AC is on or off, the other seems to have a partial voltage, like .12-.17 volts no matter if the ac is on or off.

Motor was running and up to op temp, which may or may not have the fans commanded on, usually after sitting idling for any about of time in 90 degree heat, the fans would be on.

Also, I jumped pins 30 and 87 and the fan would turn on, so the fan works fine.
I did this on both relays as both fans are not working...I'm assuming that both the AC command and the CTS would not have went bad at the same time so that neither is commanding the fans on???

 

Have you tried the diagnostics on this page?

4th Gen LT1 F-body Tech Articles
http://shbox.com/1/fan_schematic_1995.jpg

The PCM controls when to turn the fans on using input from a number of sources, not necessarily just the coolant temp sensor.

The .1x voltage you're seeing is likely just backfeed through ground.

 

With the relay plugged in do you see 12v across both 86 and 85 to ground when the fan is off? This is because the pcm supplies ground to complete the circuit, the 12volts is always there.

 

Thanks for the link to the diagram very helpful, I'm sure these are wired like the top diagram on that link as I have no 3rd relay and also one fan is connected to pin87 on one relay while the other is connected to pin30 on the other relay.
I do have 12v all the time to 85 or 86, not both don't remember which one, I think it was 86.
I beleive these were wired to be on high speed or both fans on all the time when either PCM commands on for high temp or ac was on, remember this was a transplant motor so the harness was completely rewired. It would appear that the same control wire from the PCM is input to both relays.
Will take a closer look this weekend, thanks for the info so far.

 

Alright I figured it out this morning.
Mine is wired a little different than the diagrams, but understanding the basic principal of how the relay works was the important part.
pin 30 and 87 on the relay is the power source to the fan.
pin 86 and 85 are what trigger the pins 30 and 87 to connect and make the power go to the fan. Either on of 85 or 86 can be the ground while the other is a 12v source...either can be the trigger either grounding one while the other has 12v, or apply 12v when the other is grounded.

My problem was an inline fuse on the power source for the 1st fan, fuse was not burned thru, but was a little melted as it is fairly close above the headers on the passenger side...remember this is a hacked up harness in a motor transplant so it isn't the same on an f-body. The fan did work when I tested it earlier by jumping the wire from pin 30 to 87, but did not this morning yet it still showed 12v on it...just didn't have a good enough connection for the amperage to start the fan up.

Fan #1 is triggered from the PCM A10...then the power wire to the fan that becomes active is the trigger feed (12v on) to fan #2, which the trigger ground is bolted to the chassis....
So, both my fans run anytime the CTS causes the PCM to turn on a fan or if the AC is on.