Cummins swap.. Gauges going crazy.
 

So, I've got an interesting question for you guys. I'm just about done with a 12 valve swap in my 97 F350. Going from 7.3/E4OD to 6BT/ZF5. Truck runs great, but I'm having some issues with the instrument cluster. Firstly, I got adapters to run the Ford Oil Pressure/Water Temp senders, but for whatever reason the oil pressure gauge isn't working properly. When I turn the key on, the oil pressure gauge jumps to about 1/2 way, but when I start the truck it drops to zero. I know I have to have good oil pressure, as much as this engine has been run since the swap it'd be knocking by now if I didn't. I took a jumper and ran from the oil pressure wire to ground, and the gauge went to half mast. Thinking it may be a ground issue, I grounded the batteries and the engine to the frame with 2 gauge wire, but still no change. I'm at a loss here.
Even more interesting, is that regardless of whether or not the truck is running or even if the key is in it, whenever I step on the brake pedal not only do the brake lights come on, but so do the headlights, cab light, check engine light, and wait to start light. Also when the brake pedal is depressed, the fuel gauge swings to the right all the way past full, and the oil pressure gauge moves. When I release the brake, the fuel gauge returns to the correct reading, and the oil pressure either drops to zero if the engine is running, or to half mast if it's off....

I'm starting to think that the gauge issue may have something to do with the fact that all the plugs that were on the drive by wire throttle pedal are just unplugged. Maybe there has to be some sort of voltage/ground through there to make the gauges work??

I should also mention that I did not start this swap. I bought the truck at a screaming deal with the swap half finished. I did wind up getting a new IDM/PCM out of a 95 or 96 along with both complete under-hood harnesses, as the IDM/PCM were missing when I got the truck, and Injection Harness wires had been cut/weren't labelled, etc. The harness that was in the truck going to the PCM behind the parking brake was complete, so I just connected the new PCM I had and slid it into the slot. I'm using the IDM/Injection Harness I acquired from the junkyard, and it is complete and uncut with the exception of one switched 12v wire that I stole off of the GPR to run the FSS.

Beyond the throttle pedal possibility, I'm at a loss here, fellas. HELP!!!

-Jake