[crzipilot]

Ok, I've searched for a few days and read alot, but still haven't found any solutions.

Just put together a '88 Gt for my son, so we are basically ironing out the gremlins to get it on the road safely. (And yes, aftermarket gauges are on the list, just not feasible just this specific moment.)

Anyways, instrument gauges jump and act erratically at different times.

1. When blinker is turned on (forget if it's the left or right) All the gauges (I think including the Tach) jump on the signal blink.

2. Headlights turned on The gauges either drive all the way high, or all the way low, depending on where the dimmer switch is located. as you move the dimmer switch up and down, the gauges follow the switch. It also turns on the right blink light on the instrument cluster.


car is basically stock, though there is supposedly a 3G alternator installed, Still have to go and figure out what amp rating it actually is, but there is a single wire from alternator to battery, still have to check the actual wiring of whomever did this.

We did clean all ground and tighten them up. We added a 4Ga ground wire from the fender ground location to the engine block where the battery ground locates near the oil filter. We added a 10ga ground wire from the fender ground to the Firewall ground location. And removed and cleaned the ground strap from the firewall to the back of the driver side head.

Headlight switch has been replaced with new unit.

Dimmer switch has been replaced with a used one from a '93 (though not positive the used one isn't faulty either)

next thing I imagine would be the multifunction switch in the steering column.


Any more ideas??? check the ground again (already 4 or 5 times)???

Just need some ideas on where to go to next, and I hate chasing electrical gremlins, never been good with it.


thanks

Forgot to add, the temp gauge was working, then it stopped working, replaces the Temp sending unit, and it works again, but now it sits at N and O on the gauge, acting like car is overheating, but checking with IR temp gauge, the intake and thermostat housing are sitting at 185-195 at that needle setting. Possible napa gave me wrong sending unit?

[jrichker]

If the temp gauge goes up when you do things that increase the electrical load like high blower and lights, you have an engine to chassis power ground problem.

Ignition switches – they overheat and cause flaky wiper, radio, heater blower & turn signal problems.

If this is not the case, you get to go digging through the gauge cluster connections and try to find an intermittent connection, which will probably be a bad ground. Grounds are the one common element that affects many circuits.

See http://www.stangnet.com/tech/cluster87-93.pdf for an instrument cluster diagram.
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[crzipilot]

Thanks for the response.

Yes the temp gauge does go up. as do the other gauges when a load is put on the electrical system. Headlights turned on, blinker turned on. Nothing happens to the gauges though with fan blower speed being turned up or down.

I added a 4ga ground wire from the ground spot by the battery to the location on the block where the battery ground wire is mounted. I also ran a 10ga wire from the firewall ground spot where the ground strap is, to the fender area where the 4ga wire is. I also cleaned the ground strap and mounting locations, still have the problem.

What's the best way to test your grounds???

From the harness for the gauge cluster, are the two black grounds run to the firewall and terminated there? Are they fairly easy to find or? We had the dash half apart changing the dimmer switch, so I guess we could go all out and pull everything and maybe change the cluster the '89 cluster sitting in the garage....

Thanks
Paul

[SMOKEDYA]

As far as i can remember you caint really test grounds just do an OHM test on the wire?I'm thinking it's in the cluster or in the multifunction switch. peace











john

[pudman]

maybe a bad IVR?

[jrichker]

Grounds are best tested by using the voltage drop method.

Voltage drop testing of connections and grounds.

Use a Digital Volt Meter (DVM) to measure the voltage drop across a connection or wire. Adding length to the test leads may be required, and does not affect the accuracy of the test. Use 18-20 gauge wire for the test leads if you have to lengthen them.
1.) Most grounds use the negative battery post as their starting point.
2.) The voltage will be small if the ground is good: less voltage drop = better connection.
3.) Be sure that the power to the circuit is on, and the circuit is being used in its normal manner. For instance, if it is a light circuit, the lights on that circuit should be powered on. Loading the circuit to its maximum capacity helps find bad connections that might slip by otherwise.
4.) To measure grounds, place one DVM lead on the battery negative post and the other on the wire or connector that goes to ground. Place the other DVM lead on the wire or connection you want to test.
5.) Read the voltage drop: Light duty circuits (1-5 amps) should show .1-.25 volts. Medium duty circuits (6-25 amps) should show .25-.5 volts. Heavy duty circuits (26 amps up) should show .5-.75 volt drop. A voltage drop lower that spec is always acceptable.
6.)
See Automotive Test Tools for help for help troubleshooting voltage drops across grounds.