I have double checked everything I can think of. Grounds, relays, and wiring seem to check out. My conclusion is the #3 relay works and does its job perfectly by grounding the fans.....but the fans Do not have power when thermoswitch activates. This explains the medium speed when the Ecu temp sensor hits 220F, instead of low speed. The ground is reinforced when low speed kicks on due to the Ecu temp switch.

Does the fan thermoswitch connect directly to the #3 relay or does it go through the Cooling fan control module/Ecu?

I tried a low speed diagnostic test. Connected TFA to ground and the fans turned on low. If all else fails, I'm thinking of splicing the thermo switch into the diagnostic wire, if I cannot figure this out. My guess is that it would ground and theoretically do the same thing as a jumper in the diagnostic port.

 

Hard to tell but it looks like you can replace the harness. From relay to connector.



On a side note, i cant believe FDs run over 85° C and be ok. My car ran at 88°C and after a few rips id get to 92-94°C. That engine ended up failing with bad water seals and i figured my FMIC was blocking air to my radiator. Making me over heat... over 99°C!!?? Sounds crazy to me. But it could be just me

 

^IIRC, the stock t-stat is 85 C. That's only 185 F....not that hot and probably just into the efficient operating range. And 99 C. isn't hot either. The stock thermoswitch threshold for low fan speed is 108 C. Many/most change it out for the 95 C. from the S5 for a wider safety margin, but still I don't seeing it being (by itself) a reason for your coolant seal failure. Not usually a fan of FMICs for street use, but seems like you were running fairly cool compared to some I've heard of.

 

And for me, the FD switch circuit does nothing at the moment....other than make the number 3 relay click.......my next step is checking the cooling fan control module. But, it just snowed 5 inches today, so I am now looking for a shop for winter.....