i have a 1999 mustang gt, i replaced d heads, and d oil sending unit. i have oil pressure (via aftermarket gauge), but d oil gauge in d cars does not show oil pressure. 3 oil sending unit later still inside gauge not working. cannot figure out way. PLEASE HELP!!!!

 

Hi!
I just joined this forum and I am sorry for the late answer.
What you have to do is to test the wiring for the inside gauge.
The sender gives you an negative output and if the wiring is faulty that would give you an error.
Turn the ignition on without starting the motor.
Measure with a voltmeter between the cable that you are connecting to the sender and the chassi or something grounded.
If you get a reading then the cable is probably good and it could be the earth connector for the inside gauge.
Open the dash unit and check the cable betweenthe sender and the gauge with an voltmeter set to audio for checking circuits and see if you get an sound.
If you get a sound signal the cable is ok if not the cable is faulty, exchange it.
You could also skip the tests and draw new wires from the sender to the gauge.
Since you have tried 3 different senders the fault is probably in the wiring.