1989 XJS MKIII ECM water temp switch f

Hello everyone,
My climate control system went wacky on me and is doing whatever it wants.
So far, using the JAG diagnostic guide for the MKiII, I found circuit #21 (black wire)
with a bad reading. This circuit is called the water temperature switch. Does anyone know it’s location? I don’t think it’s the same as the coolant temperature switch located on the engine since that circuit wire is a different color then black.
Thanks !

Heater pipe, upper right of left footwell.

Thanks Kilbert for the location!

Remove instrument cluster to access the left side of the Delanair unit and the copper heater pipes. There were two different colors (and different part numbers) of heater water temp. sensors, one was red (JLM763) and one was black ? - any one remember the right combination for the '89?

If the wires going to the switch are slate and black, It’s JLM 763.(red)
If the wires are green and black, it’s JLM 2121. (black)
Thanks to Kirbert.

Thanks guys I did find it. I easily saw it connected to a heat core elbow. It was being held on by two small screws.
Funny thing it failed the diagnostic test #30 but now that I have it out and checked it by heating it up to 104 degrees (F), it clicks on (continuity between the two terminals) correctly.
I also took out the lower feedback potentiometer and again that part failed the diagnostic test # 44, #45, #47, #48, #51 and #53 but checking with an ohm meter and moving the dial, it seems fine because the ohm readings increase and decrease accordingly.
Last item for me to look into is the differential temperature potentiometer that lockheed has already pointed me in the right direction.
This all begin because I was having an erratic climate control.

Thanks Dave. My temp switch was red. I already put everything back the instrument cluster so I don’t remember the wire colors.

My lower feedback pot failed the diagnostic testing but it seems fine now that its out of the car. I checked it using ohms. It increases and decreases in resistance as I manually move the dial. Maybe it’s fine and I just need to check for a jammed flap that other owners have complained about.

Here is another document for troubleshootng that may be more helpful and accurate.Delanair Mk3 systems…pdf (159.4 KB)

Hello Gents,
I am still having an erratic climate control system.
The other day it was cold outside and could not get the system to go to heat.
I finally set aside time to redo the MKIII diagnostic procedure again.
Every test passed except for #39 (replace temperature demand potentiometer), #40 (temperature differential potentiometer), and #41 (temperature differential potentiometer). Does anyone know of using generic potentiometers that match the temp demand potentiometer and temperature differential potentiometer?

If you don’t have it’s values and dimensions the only way is to take out the old one, measure it and find an equivalent.

Yes thanks Aristide for the advice. Both of my jags are running/driving works in progress and I’m trying to keep the car together while I find back up parts if convenient.