Electrical issue- help please

[coolblue65]

My oil pressure light has decided it wants to stay on- with the key in or out, I thought it might have been a bad sensor so I replaced that with no improvement. If I disconnect the wire at the sensor the light goes off. It seems especially strange to me that the light will stay on when I pull the key out.

Any thoughts of where I should look next? Ignition switch or instrument panel are my thoughts - but I am not really sure what I should look for or how to test.


BTW-I do have a mechanical gauge as well so I do have oil pressure.

 

[2+2GT]

Start with visual inspection, you may have physical damage of the wiring.

 

[coolblue65]

well I looked over the wire in the engine bay, nothing seemed strange, I haven't looked under the dash to closely yet.

Although I do have another symptom that I found on my drive home tonight, my dash lights are not working either.

 

[robbz28]

2+2 is probably right....that sending wire is probably grounded out somewhere...perhaps where the wire goes through the firewall, or the wire may be cut in half somewhere....trace it back and I bet you find a frayed or cracked wire.

 

[horseballz]

Rob,
If the wire was shorted like you suggested, the light would not go off when the sensor gets unplugged. Kind of odd?
Gene

 

[tx65coupe]

I too am thinking a wire got pinched somewhere.

 

[robbz28]

Rob,
If the wire was shorted like you suggested, the light would not go off when the sensor gets unplugged. Kind of odd?
Gene

Most of those sensors simply provide a ground for the light...if the sending wire is bare somewhere touching metal, then it does not matter if you unplug the sensor, it will still be getting ground and the light still shine. Instead of "shorting" I should have said "grounding" my bad.

 

[coolblue65]

So I reinspected the engine bay wiring again, and found nothing that appeared to be damaged. I pulled the instrument cluster....and lets just say its a real mess back there, there are at least 2 wires that 'appear' as though they should have been connected to something at some point in time, but no longer are. This is only complicated by the butchering of the wiring done over the years back there by the addition of things like gauges (previous owners) and the stereo, fan and MSD which was done about 10-15 years ago by a family friend.

The only wiring I have done recently is add LED tail lamps with electronic flasher, and a new turn signal switch.

Now here is the current list of things electrically speaking that I have determined are screwed up as of now.

1. Oil light- stays on with ignition off, turn the car on, it gets oil pressure, light goes off, turn the car off it stays off. Turn the ignition back on and it will then stay lit if you pull the key.

2. Dash lights & blower are not working....seem unrelated

3. Horn stopped working

4.Turn signals not blinking correctly- but I have concluded its a bad socket on the passenger side front. I don't believe this should be related to any of the other problems.

The wiring for the turn signal switch was a pretty straightforward replacement, and was buried in the dash so I didn't have to mess with anything else, but I suppose I will go and double check the connection.

I need to get a wiring diagram to help decipher what is what under the dash. anyone have an electronic copy of the diagram?

I am half way to the point that I just want to pull it all out and start fresh and get a new harness designed to handle modern components. But the thought of wiring that much pretty much sickens me.

 

[robbz28]

Is there an Instrument Voltage Regulator on the back of the cluster? A little silver box held on with one screw that has two wires connected to it? If not that may be where those wires (a male and female blade) hook up and may be your problem. (sorry for the elementary explanation...just covering my bases, lol) That light is getting ground from somewhere...could be in the cluster itself.

 

[robbz28]

I had a lot of those little "issues" with my car....so instead of chasing them down and fixing them and saving myself some money, I yanked every wire out of that car and got a painless harness....took me a weekend to put it in and it was very very well worth it!

 

[Tim65GT]

One side of the oil light gets Ground when the oil press sender unit senses low oil pressure. From what you are describing, this part is working correctly. The other side of the lamp gets 12V only from an ignition source. Somehow, battery power is making it's way to this point.

 

[coolblue65]

One side of the oil light gets Ground when the oil press sender unit senses low oil pressure. From what you are describing, this part is working correctly. The other side of the lamp gets 12V only from an ignition source. Somehow, battery power is making it's way to this point.

That makes me think I could have a bad ignition switch-or at the very least the problem is coming from under the dash.

I have been printing out the various wiring diagrams that I can find online so I can go under the dash to try to decipher what is what.

 

[Jetsetmantony]

Find the problem yet?

I just joined Stangnet and see your dilemma. I can sympathize with wiring problems. I've had my Stang since 1969. The lead from your 65 Oil pressure sending unit should be a white/red wire going to your cluster oil gauge. The other wire on the gauge should connect up to the ignition switch, which should be a black/green wire.

If you examined those two wires carefully and find no frays, (a short to ground, would cause a different problem. Because you mention your are getting voltage/light all the time, your ignition switch looks most likely to be the culprit, getting power all the time if the switch is always closed or making some contact. I agree with TIM65GT. Is it the original switch? They're cheap and easy to install.