Chrysler Repair: Dash gauges read low: 88 LeBaron convt., test gauge, ground lead

Question
I recently rebuilt my wife's '88 LeBaron Convertible. New engine/Tranny and suspension. My problem is since the rebuild, the oil pressure and temperature indicators on the dash read low. The oil pressure in fact indicates 0 when warmed up and idling. I have tested the pressure with a hand held test gauge at the block where the sending unit is and the pressure at a warm idle is around 12 psi. I have tried replacing the sending unit but the new one reads exactly the same. Since both the temp and oil pressure indictors are reading low, I am inclined to think its something in the dash wiring I may have missed. I have a shop manual for the car, but cannot see anything obvious. Any ideas?

Answer
Hi Alan,
Both those gauges require a 12V supply on pin J of the gray cluster plug. Try reading the voltage between pin J and pin E of that same plug which is the ground lead to see if it is full battery voltage. If not then check fuse 13 and the dark blue wire on the ignition switch to see of those show full battery voltage when the ignition switch is 'on'. Perhaps you are not getting a full 12V to 'drive' those gauges. The other alternative is that the wires to the senders from the cluster have some resistance at a connection along their pathways (pins J and K of the red plug) or possibly the ground wire lead to the engine from the - post battery clamp is not well connected.
Please let me know what you find out.
Roland