I have an '85 with a single electric cooling fan. How would I go about making the ecm control it? My current ecm is from an '89 with dual fans so I assume I just need to wire the fan like it is the #2 fan?

Were the single electric fans multi speed?

 

As I understand it ...

The primary fan was controlled by the ECM, the secondary fan was controlled by a fan switch in the pass side head (or by the A/C).

The ECM got it's temp reading from the CTS in the intake where the thermostat housing is. I assume that the ECM sent a ground to the primary fan relay when it sensed the right temp from the CTS.

But I never owned a dual fan car - this is all based on what I've read.

 

The stock single fans are One speed fans. Like newbie mentioned above, the primary fan is the ECM controlled one. That may be more reliable for you if you like the temperature it comes on at, and wiring it up is no problem. If you don't, burning a new chip to alter the fan turn on temp may or may not be easier for you than changing the stock single fan temp switch

 

I have all of the chip burning and data logging burning a new chip for me would be much easier than messing with a mechanical switch.

 

Oh yeah, If you've got that stuff and ability it sounds like it would be the best way to go. The CTS is definitely more reliable and easily accessed. Not sure how you would make sure the fan goes on anytime the AC is on, maybe not critical?