OK, I have a 1988 Iroc Z with the 305. Now, After messing through all the jacked up wiring the person did that had the car before me i finally got all the cooling fan wires right. Now Here is my problem like many others are stating. Oh and by the way i don't wanna hear, "Just wire in a switch" cause I do not want to do that, already killed one battery cause of it. Anyways, When i ground out the Green/white wire the fans kick on. With one relay both fans kick on and with the other r elay just the driver side kicks on (These are new relays too). So I know they work and the relays are working. Now, When I run the car and turn on the A/C both fans kick on and run like they should. But when i run the car and just wait for the fan/fans to kick on when it gets warm they never do, I've let the car get hotter than it should ever get in normal driving conditions but the fan still won't kick on. I replaced the Coolant Fan Temperature Switch that is on the DRIVER side head and tried to see if that worked but it didn't change anything. When i check the wire that hooks up to the temperature Switch I actually get voltage from the wire that slowly rises. (I don'tknow if that's normal or not) Basically i don't know what else to check, tried everything I feel like, let me know if you know anything more. thanx for your help.

 

Don't forget about the sensor on the passenger side head between #6 & #8 plugs, when it hits around 225 it sends a signal to turn on the passenger side fan.

 

Maybe this will help out some. Just ignore the (Wire manual fan switch here) remarks.

 

The sensor on the driver side head is for the guage in the dash. The one on the manifold near the thermostat is going to the computer and the computer does the primary fan. The sensor on the passenger head is for the secondary fan and doesnt go to the computer.

Ha, iv been through a lot of figuring this out for sure, and iv heard that the computer doesnt turn on the fan until upwards of 235*F

I would usggest going to the technical article part of this site, and look for Willie's article about the coolant fan modification in the electrical section. Its faily simple, adjustable temp, and you can always go back to the stock setting for emissions tests. Emissions is the reason GM made these engines run so hot from what i hear.

Try reading that article for sure, its very good.

 

Oh, and the above diagram is showing to wire 2 switches, one for each fan. The article in the tech section has a switch, but u leave it off and the new better system is in effect, so u dont worry about it at all

 

Sorry to bring this thread back up, but you can also have both fans come on when the ECM commands one on by using a jumper wire to connect the green wire (of terminal F) of each relay together. This is probably the least amount of work to get the ECM to turn both fans on at the same time. I just wired it up this way today using the above diagram because I have no AC and my fan switch was broken, so now they both come on when the ECM says so.

You could also then take the wire connector off the temperature fan switch (in the pass head) and run it to a switch. This way, the ECM controls both fans at the same time, and if you want them on earlier, you can also manually control them. Then just turn the switch off, and the ECM manages them. I'll be installing a small switch under my hood to turn both fans on at once because the only time I'd really care to do it manually is at the track. I can burn PROMs to turn the fans on when I want for normal driving.