It appears that my truck's instrument cluster is having an issue. The oil pressure gauge stopped working and so did the Check Engine light. It no longer comes on when the key is turned on. Is it likely they are related?

 

I have the functional gauge modification with the jumper on the gauge and the older model large sending unit.

I did some checking, and these are the results I got.

Sending unit reads 62 K ohms not running and 14-15 K ohms running.

The wire reads fluctuations between 0 and negative millivolts with the key off and 4.75 volts with the key on.

Do these numbers sound right?

 

Did you check the fuses?

 

Well, it looks like the sending unit is bad. The one in out Mustang reads 150 ohms not running, not K ohms.

We grounded the gauge using a resistor and it operates.

I'm hoping that the CEL not working is just the bulb, even though they are all new.

I didn't see any fuse problems.

 

After replacing the sending unit it works intermittently. I think the 90 degree push on connector has a bad connection inside the rubber protector. I'd like to replace it with a ring terminal, but can't find a nut that fits the stud. Does anyone know what size fits?

 

I was able to read the codes through the diagnostic port. This should indicate that the circuit the CEL bulb is on is good, correct?

 

The CEL should come on every time you start the truck for a bulb check. if it does not, then the bulb is bad

being able to read codes means absolutely nothing

 

I was thinking that if there was a break in the circuit, the light wouldn't work and possibly the port wouldn't either.

Anyway, It turns out that it was just a bad bulb. Even new ones burn out prematurely.