Tach INOP HELP!!!

[qshipsho]

I tryed starting my car with just a jump box (it didn't work) The there were lots relays clicking and the tach swung to 8000 rpm and stayed there! The polarity was correct (Red to pos and black to neg) When I put the battery back in , the needle didn't move. I tapped on the sppedo glass and the needle moved beyond 8000 to an inch below the 0 and it only jumps a little when I put the ignition on or go to start it. It basically doesn't work...any ideas?

 

['94SHO]

Does it start? Maybe your Cam sensor is bad.. It runs the tach. Did your battery go completely die? Rarely, when totally discharged, a battery will form a "bridge" from plate to plate, or plate to case. This REVERSES the polarity of your battery!!
This leads to hot or smoking pos. lead, and after attempting to start, the engine will turn backwards 1/2 a turn or so..
WARNING!! This can result in the explosion of your battery, or fried electronics, blown diodes etc.
Check the polarity of your batt., clean and tighten all clamps and grounds. Good luck!!