'01 F350 won't start no wts no tach

It doesn't make any sense that the truck will run with the IDM unbolted from the fender.

When it is unbolted do you get the WTS light and does the truck start on it's own?

You might also try swapping relays around. The PCM relay with the blower relay and try it and then swap the IDM relay around.

Here is a diagram of the under hood fuse and relays

I think that I would start checking grounds. They will do strange things when one is missing or is corroded enough that it isn't making a good contact and this sounds like a weird type of problem.

Try bolting the IDM up and then take a jumper cable from the negative on the battery directly to the IDM and see what happens.