Oil Guage problem-how to find short?

[RMM]

Merc 1988 7.4L<br /><br />The oil guage is all over the place will work right then not at all then wrong reading. Tested with manual guage at engine and OK. Replaced sender and guage and no change, so assuming is wiring. <br /><br />Question is I have a digital test meter, but how do I determine if there is a break in the wire or a ground short or something else? Have tried by-passing existing wire to guage by running new wire but then the guage just pins itself. Any help out there? Thanks

 

[hotmerc]

Re: Oil Guage problem-how to find short?

i would do a continuity test on the wire from the sending unit to the gauge. then check the ground wire at the gauge. it should be jumped from all the other gauges that you have. make sure all the nuts are tight. if they work properly you might be looking at a bad oil pressure gauge. i had a similar problem early in the season with my 87' 5.0 ltr. the only thing is ALL my gauges were shorting out. wound up salt water ate up the ground wire from the harrness in the engine compartment and was shooting 12 volts through the negitive sides of the gauges! i had to replace them all and the sending units because it fried them up, everythings good now, but i would check all your grounds. when you changed the sending unit did you put teflon tape or anything on the threads? because the threads act as a ground, so if you did, take it off! good luck.

 

[RMM]

Re: Oil Guage problem-how to find short?

hotmerc, thanks for the reply. How do I do a continuity test? Also how do I test the grounds to know if OK or not? What do I set the meter to and what should it read, or is there another way? <br /><br />They are all jumped and now that think about it the others work fine so maybe that means ground is OK and it is the sending wire itself? I have detached the sending wire and run a new wire straight to the sender and then the sender just pins itself all the way up. No idea on this. Does another wire also need to be detached from the guage to make work right? even cut and replaced the ring terminals on all wires for that guage. Maybe will try replacing the sender again. <br /><br />Oh, did add teflon tape to the threads b/c was seeping oil, but actually seems to work more often now than before. Who knows...

 

[Ralph 123]

Re: Oil Guage problem-how to find short?

You have to remove the tape. That could be your problem.<br /><br />I can't think of a reasonable explination for the gauge pinning itself except that the sender is not working properly because of the tape.<br /><br />Remove the tape and then try your bypass wire (remove old sender wire from sender and gauge when you do - if it has a short you will just be shorting your new wire too)

 

[hotmerc]

Re: Oil Guage problem-how to find short?

take off the tape becuase thats what grounds out the sending unit! also, make sure the wire coming from the ignition to the gauge is in good shape. this is also jumped from gauge to gauge. the continuity tetser on the gauge is the setting where you touch both leads together and the meter should make noise. you can also use the ohm meter.