Help! My tach went crazy and it brought my AC down with it!
 

So I was driving the runner around yesterday, and all of a sudden I noticed the tach was behaving erratically. First it was just jumping up and down a lot, then it completely died. The weird thing about this is it killed my AC with it! The air is still blowing, but only blows cold if the tach is reading the engine abouve 0 rpms - which rarely happens now :( Any ideas?? I don't even know where to start. No other gauges are reading funny, and I have gotten no CEL. Thanks all!

Clean the coil and igniter ground, And the main battery/body ground. Common problem. Not sure bout the A/C though...

Yeah I kinda thought it could have been a bad ground, I will have to do some research and find where those points are, thanks for the direction though! I really appreciate all the help this forum has given me, hopefully as I learn more about these trucks I can add to the feedback!

Easy stuff. The coil/igniter ground is simply the mount (grounds through the mount) and the battery/body ground is super easy to find. :)

WE all gotta start somewhere, enjoy!

I checked the grounds I could find, and none had any rust/corrosion around them. The battery terminals were a mess, and I cleaned them off, but the tach is still not working, and when it does, readings are very erratic :( Any other ideas? I'm not sure if I actually found the coil/igniter ground. Is it directly connected to the distributor? Thanks!

Clean the grounds I told you about. Even if they look clean..

The coil+igniter mount/ground and the battery/body ground. It is on the drivers side inner fender. It has two little packs that are side by side, one wire goes from it to the distributor.

I have had this happen twice on my truck and once on my girlfriends 4runner...

So I cleaned all the grounds, and the connectors on the igniter, and the tach is still behaving badly. I cleaned the ground on the mount of the igniter, as well as the one just a few inches away, "it connects to a pigtail of some sort."

I'm confused because the tach isn't completely dead, just operating erratically - and the fact that it took the AC with it puzzles me even more. I figured that was a fail safe for the compressor, to not kick on when the engine isn't running. The problem has to be upstream from that feed. Any more ideas? Thanks again!