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Discussion Starter #1 (Edited)
With my 95 GMC SIERRA 2500 4x4 I have an intermittent problem where the tach and speedometer and indicator light for the shifter does not work. Also, the transmission doesn't shift right. Any ideas
 

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That is caused by only a few things and it probably is your ignition switch intermittently failing. I delt with this in my burb for over a year before it became permanent. It's very hard to troubleshoot an intermittent failure like this as each time the ignition switch is operated a different result occurs due to different voltages making it through the switch, its supposed to be exactly the same as the battery. I'll explain the path of electricity off the top of my head and yours may only be slightly different due to being a 95.

The ignition switch has a pile of wires that plug into a connector on the firewall, there is a bolt that holds it in place. This brings electricity to the switch which is then activated with the key sending voltage down the return wires to the fuse panel on the end of the dash, The transmission wire is pink. The prndl fuse is the tranny fuse, #19 on my burb. The pink wire then goes into a bundle of wires and then down under the truck to the tranny through the big round plug that plugs into the tranny. Its hidden behind a heat shield, pull this heat shield off, 13mm 1/2" or 14mm 9/16" clean all around this area very well before taking the plug out to inspect. Pin E on this big round plug is the positive feed that came from the ignition switch, trannys dont have a ground and instead all the other wires are negative feeds turned on or off to activate the different solenoids. You can check the continuity with an appropriate sized drill bit stuck into pin E on the plug. It should always read the exact same as the battery, any variances are no good and mostly a symptom of a bad ignition switch. Of course there could be other issues such as the plug is coming loose, pin e is corroded or dirty, mine were but it wasnt the problem. The pink wire could have a break in it anywhere between the plug and the fuse panel or the fuse panel and the ignition switch, maybe even in the tilt part in the column where the wires are stretched to there max length. I inspected every single inch of wire in my burb and there was no problem. I honestly believe gm made the wiring in these old truck to last and they can be trusted, I cut mine up for testing, even re pining and soldering the connections at the fuse panel. Everything was fine except the ignition switch. They want quite a few buck for a ac delco($300) for my truck and down to ($150) for others although they all look identical and probably are. Well I went to a you pick scrap yard and picked up 2 switches from low mileage vehicles for like $10 and fixed my problem in less than an hour after fkn around for over a year troubleshooting BS that I couldn't solve. Frustrating but I was sooooooo happy to fix it! Especially for ten bucks.

Well that's about all I know about this.... Oh it could also be your prndl fuse.... maybe corroded? Wouldnt that be nice!

Good luck!

Al
 

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When this is happening you can manually shift from 1st or 2nd to 3rd to start going a bit smoother. This could also be used to get a truck home that may have a tranny problem and wont shift out of the lower gears to the higher gears..... simply pull the prndl fuse and you can probably get home.

Later.
 

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