• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Thermoswitch Wiring - '92 740 Turbo...

S

Steeech

New member
Joined
Jul 3, 2026
Hello Forum!
After hitting a deer with my finally rebuilt 240 '90 wagon 3 weeks ago and destroying the front end, I acquired a '92 740 turbo wagon.
California kept with almost no rust! Def worth putting some time into as Ive always wanted a B230FT...
After hauling back to my driveway, I began the fun!
Installed new exhaust and new calipers and springs/shocks/struts are on the way.
Aside from a few little things like dead horn and such, I noticed the radiator fan was not spinning
(after a boiling over coolant reservoir while she was idling away).
After jumping the fan to make sure it worked, I found the fan relay and ordered a new one just in case.
The biggest issue I see is no connection from the thermoswitch on the back of the radiator/fan assembly.
Can someone tell me where this connector on a harness might be located and how it wires into the car?
Pretty sure it traces back to the fan relay...

Cheers and thanks!

-S

Thermoswitch Pic.jpg
 
Does your 92 have the electric pusher fan in front? My 90 does..... but I think the 92 is nearly a 940 and wiring will match the 92-95 standards.

My 90 745NA has an electric switch in that same position.... my primary cooling fan is the mechanical / tropical clutch fan. Mine however has the pusher fan in front which cycles when AC is active.... and might also function when that temp switch is satisfied as an additional fan to the tropical.

I had a 92 745T...... identical setup to the 92 940T I owned. The latter did NOT have the temp switch in the radiator however.
 
Hi DET17,
Thanks for the reply! The '90 240 wagon that just turned a forrest creature to tree fertilizer had the mechanical clutch fan. I had an '88 240 before that so Im new to the fancy electrical cooling dooodads.

I am only seeing the main electric fan as pictured. Some research I've done indicates that the thermoswitch is grounded at it metal threads to chassis and the two leads connect back to '1' and '2' on the center coil activation of the fan relay
that was on the drivers side. the 2P relay has 12v measured in, clean ground contact to chassis from the fan, and the green/red connect to the fan. There is one bullet connector (white/black) on pin '2' but I cant trace it anywhere for the life of me.
A previous owner decided to delete the entire AC system: the 3 pressostats (gold, violet and grey) are hanging unconnected, and the blue/black bullet connector on the center of fan relay was unconnected and tucked into the harness sleeve.
I might just run some wire from the thermoswitch to center relay '1' and '2' and see if that kicks on the fan....

DET17: reading your 745 thread now...VERY COOL!
 
Last edited:
Yeah that’s odd, I thought only NA cars from that era with the efan had that switch? My ‘92 and ‘93 Regina cars all had it, my turbo ‘92 and ‘94 did not.
 
@PCH: I haven't checked but will next time I'm in the car.

@2manyturbos: hmmmm...possibly someone installed it after the fact or did a fan swap?
Where is the ECT sensor input located?

For the moment I wired a 4 pole 40A auto relay to trigger ground when key is in pos 2 or running.
Feeding relay coil 12v from main coil and sending a ground signal to fan relay. It works and
the car is no longer overheating.

Thanks for all the responses and thoughts! I appreciate it a lot!
 
Steeech said:
@PCH: I haven't checked but will next time I'm in the car.

@2manyturbos: hmmmm...possibly someone installed it after the fact or did a fan swap?
Where is the ECT sensor input located?

For the moment I wired a 4 pole 40A auto relay to trigger ground when key is in pos 2 or running.
Feeding relay coil 12v from main coil and sending a ground signal to fan relay. It works and
the car is no longer overheating.

Thanks for all the responses and thoughts! I appreciate it a lot!
Click to expand...
The ECT sensor is located in the cylinder head below and between intake port 3 and 4. If it wasn't working your car would not run, or, would barely run. That is the factory installed 2 speed fan on your car right now if the picture you posted is one taken of your 740's engine compartment. You may have the wrong ECU in the car, or, one that has a failed fan driver circuit.
 
^this.

That said, no reason you *can’t* use the cooler of the push-in switches to cycle the fan like the ‘92+ Regina cars do?

If the ECU works fine otherwise, idk that well routed / couple of wires to the rad temp switch is any big sin @ this late date?
The 2nd high speed I think is a function of an internal timer circuit on the relay?
(Fan runs on low for a prescribed unit of time and switches to hi?)

If you’re keeping the car a while, consider wiring up the float switch in the coolant reservoir to the warning light (well documented on brickboard) to have a warning light for coolant loss?

I tended to run a Saab T and lower temp switch in the lower radiator hose.
That way, the fan always works if there is some coolant loss (ideally it’s non-consumable, but we live in an imperfect world?) & between that & a warning the lamp for coolant loss that already exists on the instrument cluster, hopefully a catastrophic overheat is more easily avoided?

The ECU really runs them pretty hot & borderline heatsoaked on those?
Idk, whatever’s easiest?

Correct ECU w/working fan driver?

Those regina temp switches have part #s and hiperfauto posted a chart with the lowest temp versions?
 
You must log in or register to reply here.
Back
Top