Od rapidly flashing and temp gauge goes out

We have had it scanned, we are told nothing wrong with transmission. When it does it the coolant dips below C and the temp gauge goes out we are thinking maybe a wire is broke. Only does it when it rain and the undercarriage gets wet. Once drys out it works fine for weeks until it rains again. I’m trying to find out if the wires for the temp run with the same wires that the transmission goes in the same wiring harness. The flashing the od does is very very rapid faster then any of the other ones i have seen do it. I think that’s why ford said it wasn’t the transmission because of how the light was flashing. We live in the country and i wondering if a mouse got in there a chewed a wire

My 2003 had a similar problem with the blinking OD light. Only would occur sporadically while driving. Tranny guy told me when it happened again, immediately bring it to his shop and do not turn off the engine. Checked out when fault present and he fixed the problem within 30 minutes, including the time it took to have someone run and get the appropriate part.. Some electrical connection/solenoid/ etc problem

Did you ever figure this out? My car is doing exactly the same.