Gauge issues, need help.

[Doubletrouble]

I was working on the mustang today. Installed a new MSD ignition coil. (Original was all corroded) Installed new headlight and turn signal housings. Looks so much better now.
Was having an issue with the gauges before. Engine temp wasn't reading correct, replaced the sensor in the front of the intake lower. That wasn't it. Gas gauge don't read correctly either and oil pressure gauge shows no pressure, amp gauge reads low (I think, I didn't have a meter to check for sure)
Dad had read somewhere that the cluster could be bad so he had bought a used cluster. I swapped them today and same issues.
The tch works and so does the speedo, nothing else seems to work right or at all.
Any ideas?

 

[ttocs]

the harness that plugs into the cluster isn't the best design. I have seen pics where the copper traces that are supposed to slide against the other harness side can lift up and get moved enough to make contact with another trace and cause all kinds of strange problems with the gauges.

 

[Doubletrouble]

I looked at the printed circuit where the harness plugs into. It didn't look wonky in any way but who's to say it don't move when you plug it in at the weird angles you have the cluster.
Honestly I don't believe that is the issue but I won't rule out anything at this point.

 

[95opal]

If you pull the cluster you can slap a volt meter on the alt charge wire and verify you have voltage. That would eliminate any wiring problems. A used cluster doesn't necessarily mean a working cluster

 

[Doubletrouble]

Is there a wiring diagram to give the location of the charge wire? Assuming it is one of the wires in a plug to the back of the cluster that your referring to?

 

[95opal]

Is there a wiring diagram to give the location of the charge wire? Assuming it is one of the wires in a plug to the back of the cluster that your referring to?

It's a light green /red wire in the cluster harness that comes from the voltage regulator.

 

[cobrajeff96]

These might help a bit.

 

[Doubletrouble]

Very helpful, thanks! O should be able to get back to it next weekend. I'll see what I can diagnose.

 

[Doubletrouble]

I got the voltage gauge to work. I found the the plug on the alternator was unplugged. I must have hit it when working on something else. (Lock clips are broken on the plug so it didn't take much to knock it off)
I still don't think the fuel gauge is correct, the temp gauge is not working same as the oil pressure gauge.
I found the ground wires on the passenger side and cleaned those, it did not help.
Both of the temp sensors have been replaced, still no gauge movement.

 

[cobrajeff96]

Over time the variable resistor attached to the tank's float arm will deteriorate like anything else. Might be time for a new one.

The temp gauge is a very simple circuit. You could probe the wire for continuity easily with a cheap digital multimeter. If that connection is intact, maybe contact Mark accutach.com and maybe he has a fix if it's a gauge problem. Make sure the gauge needle isn't all the way bottomed out on the gauge shaft which will prevent it having the freedom of movement it needs to deflect.

 

[ttocs]

I have found that harnesses that have the clips missing can cause problems once the motor warms up and everything expands JUST a hair. Replace that harness on the alt with the broken clip.

IIRC you can just ground the wire to the temp sender and it should peg the gauge to one side or another if the wiring is good.

 

[Doubletrouble]

Ok I finally got back to the Mustang. I grounded the temp sensor and the gauge went full hot so the gauge is working. Both sensors have already been replaced. Would this now be a wiring issue? Is there anything else I can check before tracking down wires?

 

[cobrajeff96]

Doesn't seem like a wiring issue at all. It read correctly at full continuity to ground. It's likely incorrect sensors you're replacing with or just bad luck. Potentially it's not getting body ground through the threads due to corrosion, maybe. But again that doesn't seem likely given your last test result.

 

[ttocs]

yea it sounds like the wiring is ok and the gauge is reacting correctly. As mentioned maybe it was a bad or wrong sensor, or else just make sure that the connection to the sender is nice and tight. It is nothing more than a thermistor or a resistor that changes resistance based on heat that the gauge reads and then converts. If the connection is bad/dirty it can add resistance and might be enough to throw it completely off.

 

[Doubletrouble]

Thanks, I'll do some more diagnostics when I can. Been very busy lately.

 

[ttocs]

do you know how to use an ohm meter? If so try measuring the resistance of the sender from the pin to the body and see if/what it shows. There should be some resistance there that will depend on what the temp is and with any luck we can check and see that it is right, wrong, or not even there....

 

[Doubletrouble]

Yes, I can use an ohm meter. So check sensor pin to body (not engine as ground?)

 

[ttocs]

From the pin to the body of the sensor, which goes to ground when you screw it in assuming this is the same 1 pin sender that I am used to. IF there are two pins then measure across the two.

 

[Doubletrouble]

Ok I gotcha. Thanks for clarification

 

[Doubletrouble]

Sorry this is taking so long to reply. We are very busy here lately with house shopping.
I got the ohm meter out today and it just displayed "OL", so open loop. No connection at all from pin to body.