I have a 1988 Turbo II S4. The oil pressure gauge maxes out when I turn the key to the "on" position. I replaced the old factory wiring looms and a "resistor or ground sensor" broke off, I currently just have the bare wire grounded to the rear iron. Prior to this the oil pressure gauge read fine. Don't know if this could be the issue or something else. Thanks.

This is the "sensor"

 

This is on a cold motor that had not been started in about a week. The oil pressure seems to be reading backwards.

 

that Capacitor in your Picture is the KEY to the whole Problem you are having..You need to get another one of those Things..Reason?: it is used for the oil gauge to allow it to Read properly..it attaches at the clutch slave bolt(one of the 12 mm bolts that attach the slave to the Transmission) and it goes to the Firewall..WITHOUT IT,your Oil Gauge reads FULL..or high(whatever),and you could end up damaging some Electrical components(oil gauge in the cluster)..In Closing,That Part may not Seem Like a big Deal,but it Does play a Big Part in the Car's oil Pressure Readings./.Good luck.

 

Thanks, for the help. I barely moved the harness and the capacitor just fell off, I guess from the corrosion over the years. Anyone know where I can get one of these?, and price?

Thanks again for the help.

 

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/capacitor-rating-one-attaches-slave-cylinder-277942/

 

This is covered in the FAQ for FC sticky thread found at the top of this section. The FAQ for FC sticky thread covers many of the commonly asked questions, such as the question that started this thread.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/frequently-asked-questions-2nd-generation-rx-7-faq-fc-494667/

You always want to read the FAQ for FC sticky thread before posting
.

 

The gauge is scrogged if you had the wire of the capacitor grounded for any length of time. Look for you oil pressure to read ugly from now on.

 

Your oil pressure gauge is now fried. You'll need to replace the gauge, and replace the broken capacitor (the "resistor or ground sensor").

In the future, it's best to not just randomly ground wires unless you know what you are grounding.

Also, there's no such thing as a "ground sensor".