I have spent the last hour or so searching, but I can't find the thread that tells how to do that, and I'm pretty sure I read it here, but maybe 4 or 5 years ago? This is on a '94 F-350 7.3 IDI.

 

You gotta pull the gauge cluster out, locate the oil pressure gauge on the back of it, locate the stupid resistor for it, and then jump/bypass said resistor. Then you switch your oil pressure sender to one from an '83-'86 truck. It's been on my to-do list for a long time now, but seeing how my gauge cluster is stuck beyond belief Ihaven't yet found the motivation to mess with it real good.