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Old 08-19-2005, 05:04 PM
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Plymouth speedo/tach malfunction

I realize this may be a long shot since there is not much info to go on but I am at a real loss here(again). I replaced the A/C in one of my co-worker's car, 1989 acclaim, which involved removing the dash to access the evaporator core. This is a fairly simple task since the wiring remains in place attached to the firewall and none of it is removed with the dash. All the accessories and switches are simply unplugged, as is the steering column, and the plug ends stay attached to the wiring harness which remains in the car. After replacing everything and test driving the car I found that the electric speedometer and tach would not work, the speedometer will move slightly but the tach is totally dead. I checked everything and finally removed the dash again thinking maybe I had over looked a ground or possibly pinched a wire but everything looks ok. There are no grounds to the dash itself(that I see anyway) but the radio has a heavy braided ground wire attached and this is hooked up properly. there are only two cables hooked to the instrument cluster and these will not cross or plug in wrong so I know they are right, also the other gauges that feed from these two plugs work fine. Maybe there is a ground I am overlooking although I did not unhook any(intentionally anyway). Now I am looking at removing this dang thing for a third time and I don't even know what to look for since everything appears to be plugged in properly and no wires are pinched. Any ideas would be greatly appreciated
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Old 08-19-2005, 07:21 PM
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Ground

Doc here,

I would try a hard case ground with a jumper to see if it comes back..can't hurt..

Short of that, maybe pull the plugs and see if a pin hasn't pin pushed out or bent or have something insulating it..

Also Check any fuses marked Instruments...you may be backfeeding power from the other instruments to the Tach/Speedo (loaded ground) Accounting for limited almost nonexistent meter movement.


Are you getting a check engine light?


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Old 08-19-2005, 08:35 PM
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Not getting a check engine light. I checked all the plugs for pin damage when I pulled the dash the second time but I did notice something strange when I checked for voltage at the A/C pressure switch before trying the A/C, it had 9.6 volts showing with the switch off but this disapeared when a load was applyed by pluging in the A/C clutch.(the clutch did not engage until the switch was clicked on at which point the voltage went to full battery voltage) I am using a Digital meter if that matters. So far I have checked and cleaned all plugs and traced the entire harness looking for broken or grounded wires but everything looks good thats why I am so puzzled by this. I know I must be over looking something so guess I will rip that thing out again tomorrow. This cluster is plastic mounted in a plastic panel and does not touch a metal ground at any point, it has a printed film circuit on the back with two plugs how would I do a test for a faulty ground on this?
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Old 08-19-2005, 08:45 PM
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Schematic

Doc Here,

Go to autozone repair, download a schematic for your car, find the pin (s) by color and number that bring ground into the cluster..Check there .

-->Download a Schematic Here<--

Don't forget to CHANGE the vehicle to the one your working on..make/model/year..

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Old 08-21-2005, 10:01 PM
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Doc, After two days of tracing about every wire in this dang thing I finally found the problem. there is two small circuit boards located on top of the instrument housing and I noticed the tach needle jump when I accidentally touched the one on the right side while the engine was running. I unplugged this thing and cleaned the contact surfaces and BINGO! finally, problem solved!

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Old 08-22-2005, 06:29 PM
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KEwl

Doc here,

Glad to hear it was an easy fix, and thanks for letting us know.

I kinda figured it was a bad pin/board contact...Vettes are really bad for that (no metal for the water to condensate on..) and I guess it just takes longer in metal cars to raise it ugly head!

Glad to hear your motating again!

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