Tach reads 4K with engine off

[spider2081]

Just picked up an 81 Spider 2000 that has not been run in years. I connected a battery charger to the deader than dead battery just to see what electrics work. As soon as I put the ignition to the run position the tach goes from 0 to 4000 RPM. I'm not ready to see if the ar will start but curious if anyone has seen anything like this. Could the battery charger make enough electrical noise for the tack to indicate from it??? The pick up wires in the distributor have little insulation on them.
Thoughts appreciated

[So Cal Mark]

depending what type of charger you're using, you could be putting as much as 18V into the battery. I wouldn't consider doing any electrical diagnosis until you get a fully charged battery in the car

[spider2081]

Thanks Mark,
That is exactly what I would tell anyone.
In my excitement to see how good the car is I bought, I made a poor hasty decision.

[mbouse]

your spider has the Carly Simon disease... anticipation. that tach is anticipating where it will soon be happiest; at 4,000 r.p.m.