I'm looking at #5 blue on the harness, it says TO:" high speed fan relay" - IF used. The CAR is a 1985 4 cyl auto. Does this wire "Get Used " ? Thanks
also, the car has AC, if the" Line Pressure SWITCH" is not "Hooked up" (temporarily), will this affect the Starting/running of the 3800sc ?

The 84 Fiero is the only year that had dual radiator fans. Since most modern PCMs have dual cooling fan outputs it only makes sense to use both fans independently.

On the 84 C500 D1 is the low speed fan control wire and D2 is the high speed fan control wire.

this car has only 1 fan, so what happens with this wire ?

idk - I thought the 84 had dual fans but perhaps it is just a two speed fan. Both the low and high speed wires are used in the stock configuration.

You won't need that wire.
The 84's had the two speed fans (but only one actual fan), but it was a resistor for the low speed, and the high speed had no resistor.
The original 84 coolant switch switched on the low speed fan at 221F (off at below 212F), the high speed was switched on for AC and a temp above 246F (off at below 239F).
The 85+ chassis only has one speed, on or off based on the coolant sensor (switch).

Mine is an 85 with a 3800. Single speed fan. Wired without that wire since 2001.

-Dave

So I can just "cap off" that wire. thanks wonder WHY gmtuners still has it included in the harness charts?

Respectfully anyone can wire their car however they think proper. Sure it will work with only a single speed fan. And if that is what you had stock and it works fine... but

When I make an 84 harness I do hook up the low speed fan control wire and the high speed fan control wire. The 84 fan is set up for two speeds. The body is wired for it. The PCM has two outputs. So why not hook it up.

That way when only the low speed fan is needed, that is all that is ran. When the high speed is required then the fan runs at high speed. It saves on wear of the fan motor and uses less electricity and thus less power and therefor slightly better mileage.

On 85+ where the dual speed fan option isn't available I only wire for the single high speed fan.

I am in Wisconsin anyways. I can count the number of times my one speed fan comes on in a year.

so, this "high speed fan " wire can go to D2 of c500 and all is well ?? (1985)4 cyl car. This" particular car" (1985) has always had the fan running "whenever the key is on", I've been trying to straighten it out for 4 years with no luck. replaced the fan motor once, besides that....

My mistake. Not sure why but I have been thinking you have an 84. Crap.

Anyways the low speed fan output of your PCM connects to the single fan control wire on C500.

That is all.