Mike is correct when saying the sender is varying the resistance to ground. A sender for an idiot light (or idiot gage) is just a switch (NC) that opens when you have pressure. To test the sender you can disconnect its wire and put your (-) lead of your meter on the sender and the (+) lead of your meter to battery voltage (+). Motor is off 0 volts. Start motor and you should see voltage increase as the oil pressure goes up. I like to use the older analog (gage with needle) for this kind of testing. To test the gauge I made a tester out of an old gas tank sending unit. This works the same way as the oil pressure sender but it allows you to move the float arm to increase or decrease the resistance. I attached one clip to the frame of the old sender and another to the sender lead. To test the gauge one wire goes to ground (-) and the other to the sender wire. With the key on the gauge should move when you move the sender arm. Simple Larry - Cleveland -----Original Message----- From: DeTomaso [mailto:detomaso-bounces@server.detomasolist.com] On Behalf Of Mike Thomas Sent: Wednesday, August 31, 2016 8:26 PM To: detomaso@server.detomasolist.com Subject: [DeTomaso] Oil Pressure Gauge I'm trying to figure out why I'm getting a pegged reading on my oil pressure gauge. It will show normal pressure as the car starts, but soon after pegs to the right and stays there. Everything runs fine otherwise. I've swapped out the pressure sender, NAPA OP6091, and it's still pegging, so I'm suspecting the gauge. Anything else I could check? Thanks Mike Thomas Pres., Panteras Northwest Yellow '74 #6328 _______________________________________________ Detomaso Email List is not managed by POCA Posted emails must not exceed 1.5 Megabytes DeTomaso mailing list DeTomaso@server.detomasolist.com http://server.detomasolist.com/mailman/listinfo/detomaso To manage your subscription (change email address, unsubscribe, etc.) use the links above. Members who post to this list grant license to the list to forward any message posted here to all past, current, or future members of the list. They also grant the list owner permission to maintain an archive or approve the archiving of list messages.