Ok, so for the past week I've been researching this topic.. There is a ton of people with this problem, however, seems once they fix it they never post again!
I recently bought a 1994 Jeep Wrangler YJ (5 speed w/ 6cyl)- everything was working fine.. I removed the dash to install new speakers and CD Player.. (pain in the a$$) While everything was apart I cleaned it up.. Including taking apart the speedometer and cleaning.. I put everything back, plug in all wires, and start her up..
All radio installs worked perfectly, but for some reason my speedometer will start at 0mph and as soon as I put it in first gear and go it will jump straight to 25-30mph and stay there the entire time until I come to a stop..
Odometer works perfect, tach works perfect, all other gauges work perfect.. I've checked all wires, grounds, back motherboard seems to be in good shape.. I've taken the speedometer apart and cleaned tried moving needle several different ways.. Still 25-30mph?? I find it hard to believe anything was broken during my cleaning.. Im thinking its a ground or something.. But if you have had this problem & have fixed it PLEASE tell me what you did that worked.. There is a lot of try this try that.. But NOBODY says if any of it worked..
Thanks for your help! Very much appreciated as Im going NUTS! Ha
Side Note: Now my Jeep randomly doesn't start.. (No crank, but lights and gauges work bright, so I know it's not the battery/alternator.. I give it a little shake and by a little I mean I go Incredible Hulk and practically push the jeep over and it starts right up!