Ford Repair: instrument cluster, charging system, trk

Question
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Followup To
Question -
I have a 1993 F150 with over 500K miles(well maintained)My instrument cluster showed the classic symtons of indicator swinging erractic and shifting unexpectly. I have replaced this before without a problem.I got a used cluster and after I installed it my altnator quit carging,so I took it back a got another one and I have the same problem.The odds of getting two bad one is high and I am pretty sure it is the cluster as when I put my old one back in the problem goes away.These are pretty much idiot proof as the connectors will only go in one way in one place.Any suggestions would be greatly appreciated. Thanks Isaac
Answer -
Hello and thanks for the question...I'll try to help.
Before you go replacing the second cluster......did you check to see IF the charging system was faulty?
Erik
Thanks Erik,Yes,I thought I had fried my altnator so I replace it and the serpentene belt(didnot need it just insurance) and it did not help so I had the altnator and the battery tested-Ok and of course cleaned the terminals etc,I am getting 13.9 volt output from the altnator with the old cluster and with the replacement the voltages starts going down as the trk runs(running off battery) Isaac  

Answer
Hello and thanks for the reply...I'll try to help.
Since the charging system has tested and been found to be good.....you have to look at it at this angle......Since your cluster went bad..what are the chance that another has gone bad? From the same year...........
Since you are getting used....it is likely that another will be bad.
Erik