Tach Needle Goes Nuts

What makes my tach needle fly all over the place? At idle most of the time the needle wildly swings without any kind of change in the engine sound (i.e., not revving or sounding any different than an idling engine). I've had this problem for more than two years, but it's been intermittent and infrequent. Now it seems to be here to stay! And it's annoying. Any clues? v

Check the ground on the tach case.

Vicki:

You may find this post at Spyderclub.com interesting:

http://www.spyderclub.com/phpbb2/viewtopic.php?t=8595&highlight=tachometer

R.E. and Terry--thanks for the help! I'll get someone to check out my wiring and let you know how it goes. v

Vicki reading that Spyder Club info just to see if my problem was similar has convinced me that it very well may have been. Went to see Larry and on the way to his place not only did the tach needle go hay wire, it has been doing that for a while, the car started to act up and run poorly until it finally came to a stop. To solve the problem Larry re-made all the connections on the coil, and then for good measure he took two wires a big fat red one and a skinny black one. The big fat one went to the starter motor and then to the ignition key, the small black wire to the coil and also to the ignition key. I've driven the car for about 100 miles since Larry put his hands on my car and so far the tach has been rock steady. Good luck with yours.
PS Larry did tell me to wiggle the key in the ignition, to see if there is a short in the unit. Try that before you take it in, to eliminate that possibility.
Don't remember if you drive a Beck or Vintage, if Vintage there were some Vintage years a few years ago that may have a problem in the electrical wire bundle and those connections Larry reasoned may be the cause of the tach bouncing and finally my car not running at all.

Vicki,

As referenced in the spyderclub link there is some possibility that the tach is going bad. Mine has behaved sporadically at highter RPM's all along and is getting worse over time. I have rewired the ignition system as well as connecting wires and have had a standard 009 distributor, 009 with 2 different Compufire modules, 2 different MSD ignitions, MSD distributor, and a full Compufire ignition system. Tach behaves poorly with all the above above 4000rpm....no I didn't change all the ignition stuff just for the tach problem. But in my case I am 99% confident it is the tach.....I would think there is a good chance that is your problem too...