Need Help!

[jtmarine02]

So a friend of mine in town replaced the Gauge cluster, headlight switch, and dimmer switch with blue LED's. When he put the cluster back together the RPM tach began to jump around once the truck was turned on... It then stopped on its own and stood still, when you rev or drive the tach will jump around and go up and down with the right RPM level except it jumps around and doesnt stand still on the correct reading. Has anyone experienced this or heard of it happening before? Oh and he replaced that tach motor, but they all did the same thing! They were all new motors and worked fine before and after. I havent tried anything besides turning the truck off a couple times and driving to see if it clears. My next step is to unplug the battery and even possibly the PCM....? Anyone? Oh and they were calibrated correctly upon reinstallation.

[jtmarine02]

I ended up figuring it out after staring at the board for a while and comparing it to pictures that were on the "how-to" write up. It turns out, when my bud replaced the LED next to the RPM Tach, he over heated that electrical run and blew 2 Zener Diodes. I'll take a pic and post it tomorrow, but for now just know that they are the last 2 DIRECTLY under main conector pins on the far right. These happen to control the voltage regulation to that motor and possibly more components that share that run. As for which others,well that I'm not sure of; I would need schematics to figure that out. Well if any one ever runs into this or any other similar problem with their components in their dash cluster circuit card, refrence this or send me a message. I'll try and help you as much as I can. I fixed Electronics down to component level in the Marine Corp for 5 years, so I'm remembering this stuff the more I deal with it again. Plus If I get stuck I just ask old Marine buddies who worked with me and continue to do that type of work.