Isuzu Repair: 1988 Trooper II 2.6L 4ZE1, voltage drop test, oil pressure sending unit

Question
QUESTION: Wife's car quit unable to restart. I traced circuit to the Low Pressure Oil switch. I have no power going  to the LP oil switch. Checked the circuit fuse and it is fine. Replaced the LP oil switch. I still do not have power to the switch. I checked the fuel pump and it runs fine. The LP oil circuit shows that unless the switch is activated  no power to start the engine.
Circuit diagram shows power coming from instrument cluster to LPO switch. Where does the LPO switch get its power from? Are there any diodes or capacitors in that circuit? I am stumped.
This happened once before and it was the Low Power oil switch that was bad . I replaced it and the car runs fine

ANSWER: Have you checked the oil pressure sending unit or the actual connection where it hooks up? Sorry for the delay as well. I would start by doing a voltage drop test on that wiring and it will tell you loads as to whats bad and what does not have power going to it.

---------- FOLLOW-UP ----------

QUESTION: Yes I replaced the LPOS  the leads to it have no power. I am looking at the Fuel pump relay and the fuel pump diodes.
This car has two oil pressure devices , one is the common single oil pressure sender to the oil pressure gage. The other is a two lead low pressure oil switch that connect through the instrument panel and is activated when there is 4 to7 pounds of oil pressure. When the LPO switch activates it provides power to the fuel pump. I have the original factory repair and electrical sytem manuals. Now if I could only find a code reader for this Isuzu Model it would be much easier to track down the problem


Answer
Well If I had the codes that it is throwing then I could give you a source to go after Erich. I have a code book for Isuzu's so if the codes are available I can tell you what they are. If you are not getting voltage to the switch then the only thing without actually looking at your vehicle is to test the wiring with a DVOM all the way back to the source and I am sure you are going to find a break or a bad relay/resistor of some sort. I will be doing some research in the meantime and try to give you a better answer as this probably didn't help you much. I have't given up on you though!!!