Military Vehicle Repair: typical oil guage electrical schematic, circut board, unit changes


Question
I need an oil guage schematic for a Chev. 4 cylender engine I am using in a IO boat. Not Military but your training should have the answer.
Basicly I need to know what type of signal the preasure sencer sends to the guage and how the guage uses this signal.
Thanks.
Bill C.  

Answer
Your right, I don't know your boat.  But I can tell you how MOST oil pressure gauges work.  The circut starts at the ignition switch, which must be turned on.  It then goes thru a fuse to the instrument panel, where it attatches to a circut board or directly to the gauge.  From the gauge, it goes to the sending unit, where it grounds.  The guage reads resistance in the circut, produced by the sending unit.  The sending unit changes oil pressure to an electrical signal (resistance).  A quick check will reveal a bad sending unit.  Disconnect the wire at the sending unit, and with the key in the on position, momentarily ground the wire.  Watch the gauge, or use an assistant.  It should "peg out" if the circut is good to that point.  You can assume the sending unit is bad if this is so.  If the gauge does not "peg out", then check the fuse, wiring and gauge itself.  Good luck to you.

David