Stock ECU Fan mod "backup"?
 

Am I correct in assuming that when wired in parallel via boomslang with the stock ECU fan wire staying connected along with the Megasquirt signal wire, that the stock ECU will provide a failsafe fan turn-on at stock temps if anything in MS goes awry?

I'm also jumpering 1J to 1R for dual fans per this thread.

correct.

Sexy.

Be aware that, assuming this is in your '92, the cooling fan is not controlled by the stock ECU, but rather by the thermoswitch on top of the thermostat housing. The ECU wasn't given control of the primary cooling fan until '94. In the '90-'93 application, the ECU turns on the fans only when A/C is on.

this also means that if the thermoswitch is grounded, the fans are on, even if MS doesn't tell them to.

Yeah, it looks like it'll still work, as brain said, but thanks for the correct info.

After looking at the diagrams a little more closely, jumpering 1J (AC relay) to 1R (fan) at the ECU connector might energize the compressor clutch, though, when the fans kick on. Should I confine the dual fans wiring to the engine compartment if I still have AC installed?