My solution to this rediculous setup GM plagued us with, was to buy a 4 season wiring harness with relays and spliced it in to the van's wiring harness (with all the wires still connected to the ECU) and wired the both positive wires to the battery. 1 positive was supposed to go to a switched source, but the fans only run for a short duration after shutdown. The harness uses a probe that you gently put through the fins on your radiator. I would recommend buying an after market probe style gauge that you would put near the fan probe if you don't trust the factory gauge. Just be sure you warn anyone under the hood that the fans can come on at any time.
I know i will receive flack about this setup, but if your van is like mine where fixing the a/c costs more than the vehicle's worth, the $35 harness sounds brilliant! I really hope this helps someone out. Believe me, i love my van but it frustrates the crap out of me. So much money into head gaskets, fans, sensors, water pump, alternator, fuel pump and now timing chain! I will fix it again and until the rest of the body falls off! Best of luck, message me if needing advice or clarification on this.