Electrical 91 Mustang warning lights

Praetorious

Member
May 22, 2020
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Hey Guys, hope everyone is doing well,had a couple of questions on a 91ive had since new,i hope im putting this in the right spot and forgive me if I'm not.

I am trying to get all my warning lights on my cluster working again,i removed my cluster recently and replaced all my bulbs, cleaned contacts and all that.

When i cycle my key nothing comes on momentarily like its supposed to, my coolant light has the sensor disconnected because i have a electric fan and a differently style reservoir so that one is checked,i did ground the plug and i got the light to come on,check engine light bulb has been out for decades but i did put it in to check and that one does come on when cycled,low oil light was working until a few months ago and now it doesn't and the airbag light does not come on either.

Couple of questions are.... how do i check the low oil sending light on the cluster,can i pull the sensor from the pan and stick a jumper in it and ground it and it should come on? i know its just one wire but wasn't sure how to go about it electrically? the sensor has been leaking a drop here and there so i suspect it finally just went out but i wanted to check the dash light also, second question is, what controls the airbag light on the dash and how can i check that one?

Thank you guys very much for any input,i am about 2 months out from installing a 347 in my car and i'm exited as i can be,regular engine has over 200 big ones and its all original and its starting to smoke sometimes in traffic so i bit the bullet and bought a new engine,that will be fun installing that.lol
 
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Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Oil plug needs to ground to get the light on. Unplugging it leaves it open so you need to unplug it and then ground it to something.


Make sure the ribbon on the back of the cluster in in good shape. often times, the contacts where the plugs connect fold up or get bent and that causes bad connections.
 
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Praetorious

Member
May 22, 2020
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3
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Thank you so much guys,i think one of my problems is what they call the "prove out" which is what turns those warning lights on when you cycle the key or i might have a ground loose somewhere.

Funny thing is that yesterday i went to the gas station to fuel up and when i was leaving i cycled my key to start the car and low and behold my lights came on, the brake light that is and the low oil light, the check engine didn't come on and the low coolant lights for the obvious reasons i explained on the first post (check engine bulb out and low coolant sensor disconnected) and the airbag light didn't come on either and thats a mystery i need to solve also, when i got home i cycled the key again and the lights would not come on this time so its a intermittent problem.

5L5, thank you for the info on grounding the low oil sensor, i wasn't sure how to go about that, out of curiosity how does that sensor work in the pan? when liquid is around it the liquid somehow closes the circuit and when it becomes low it opens it? i have had the shop manual for my car for ages but i had totally forgotten about that one troubleshooting the vaccum and electrical circuits so i ordered it last week, it should be in soon,i have both for my 95 Thunderbird, those manuals are gold.

Something else my car started doing here recently is ill be driving and the music will cut out,not the power to the music but the sound itself,sometimes it wont do it and sometimes it will do it it off and on for several miles,weirdest thing, all wiring to that is spotless and im aware thats another story , nothing to do with whats happening to the warning lights.

Many years ago on this same car i had a horrible problem where the car would die, would not start,horrible gremling, the repair shop couldnt even figure out,sometimes when i would brake the stereo would cut out completely etc, after much money spent it ended up being the ground strap that went from the motor to the chassis,the one behind the engine corner on the driver side, 2.50 cent back then solved that problem.
 

Praetorious

Member
May 22, 2020
5
3
13
I tried to edit my comment to add something but it said i was out of time, sorry,Mike i didn't see your comment entirely cause it was partially hidden but i saw it just now,yeah i will check that cluster to make sure is good and tight,wanted to add something, about a year ago my old cluster went out, the ribbon responsible for charging the system broke so i needed another cluster pronto and the only one i could get my hands on was a 4 banger one, i replaced my speedometer and tachometer and installed it and it seemed to work fine,i did noticed that the 4 banger one had a extra resistor in the back that my old one didnt,i wonder what thats for? it was a gorgeous cluster too with the ribbon imamculate so i didn't wanna pass it up.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
39,475
15,330
224
The wiring diagram shows the oil level sensor as a variable resistor. How it works exactly I’m ot sure of, but it clearly shows it as grounding to make the light function.


The “hot” side of all the warning lights gets 12v constantly. The lights are all activated by switching grounds.