Fairgrove,
As stated, you need to put a resistance in parallel with the sending unit to lower the resistance.
HOWEVER, I would advise against doing this as this will result in a non-linear pressure vs. resistance relationship. So if you get it to read the "normal" value, it will be off as the sending unit resistance changes. How much it will be off is difficult to tell without knowing the exact resistances and the pressure vs. resistance curve of the sending unit.
Will the difference matter? Hard to tell. It's your engine. If it were mine, I'd want to know. I'd probably opt to keep it the way it is knowing that it's reading "high".
Actually, I'd probably continue my quest for the proper sending unit. It must be out there someplace.
Good Luck,
~Rick
