My XJ8 LS is done and I'm driving. Temperature never goes above middle of gauge when driving and fans don't come on. Tested not moving at idle. Temp rose quickly and fans did not come on. Must have a wiring issue between GM ECU and Jag wiring. Going to be dropping off for headliner and running A/C lines. Don't want those guys idling too long and overheating. Planning on jumping relays for fans to always run with ignition on until I figure out the issue.
By the diagram below the fans are either both off, both on low, or both on high. I think wiring Ign+ to WU wire labeled "H" for high should do it. Appreciate if someone would check my work.

 

Your marking for L and H fan speeds is correct. However, you have to ground these lines in order to activate the fans. Also, it is better to switch the fans to the low speed first (lower starting current impact), then to high speed from there. I would keep the L line connected to ground so the low speed comes on with ignition "on" and install a manual switch for grounding the H line. In this way, you can have the fans at low speed while moving and switch-on the high speed only while stuck in traffic.

 

Thanks. I should have figured out ECM run fans by switched ground.

 

Update. Figured out the suppy voltage to run the relay control was coming in at 0.4V. I'm going to tap 12V over there from a fuse box.

 

Ran 12V from the extra fuse block in my LS swap to relay. Works fine. LS ECU turns the fans on at 89C and off at 84C.