What causes engine light to illuminate on 1990 7.3l NA?

[Shawn MacAnanny]

Because of some alternator wiring issues I saw, I assumed the alternator was bad on the 1990 truck I purchased and that's why the light was on. Im finally getting around to working on it now and alternator is fine putting our 13.8 to 14.0 at idle. The oil pressure gauge works, the temperature gauge works. Oil level is fine. What else could cause the light to illuminate? Anything to do with the fuel filter or is the and engine over temp coolant temp probe that could be bad?

 

[yARIC008]

Not sure, never seen mine light up. I've had check trans light up when some wiring was bad.

 

[icanfixall]

Nothing else is connected on that circuit. Just some info on this dash light coming on. Mine did it for a couple of years and I tried many different ways to figure it out. finally it was flickering for about 80 miles driving home one evening. So I parked it and was under the hood moving wires in the dark when I saw arcing. This will surprise you. The wire telling the dash gauge that the alternator is charging was broken between the lug crimp on the insulation and the metal part of the lug or spade connector. I have NEVER seen any wires break like that but stay mostly in contact with the lug. Had it not been after dark I sure could not have found this.

 

[Shawn MacAnanny]

I'll check my wiring over, if i cant find anything, how do i disconnect it? Can i just pull the bulb or will that prevent the alternator from charging? I heard something about the OBS truck needing the airbag bulb to charge or something weird. Haha i will of course be putting in real gauges shortly.

 

[Matt_INW]

The battery light, not the engine light? The actual plastic snap in connector on the alternator could be loose or bad. Mine is borderline, over time it wiggles loose and starts throwing the light on. I take it off and put it back on and it's ok for a few more months. But one of these days I'll have to replace the plastic retaining clip that keeps it on the alternator.

If it's the engine light it's oil pressure or coolant temp, or the dash is dying (like mine) which causes some gauges to do funky things randomly.

 

[Shawn MacAnanny]

Its definitely the engine light. I didnt realize it had a battery light, that would make sense. I havent put a mechanical guage on to check oil pressure but the oil pressure gauge is as 0 with key on then it goes about 60% of the way up once its running. It does seem like it varies a little with rpm. It also varies with head lights, and turn signals.

Is there a second coolant temp sensor on these trucks like the obs that are the overtemp light?

 

[typ4]

Engine light is for oil and overtemp. there is a temp sensor on the drivers head that runs that light. There is a little circuit board on the back of the dash that is a processor for the engine light.

 

[riotwarrior]

If it iz check engine light.

The overtemp sensor is either not connecting correctly or shot.

I had this replaced OT sensor and was golden after.

JM7.3CW

 

[Thewespaul]

Or just put a real gauge sender in its the OT sensor port...