[Vtow] 76' spitfire tach malfunction

[Jim Daley]

I am wondering if anyone has any advice regarding the tachometer on my 76'
Spitfire.  When I turn on the ignition switch, the tach pointer jumps up to
6,000 rpm and stays there.  And when I turn on another load, the pointer drops
slightly but goes back up when the load is removed.  Thinking it may be a
grounding problem, I ran a jumper wire from the negative terminal of the
battery to the tach body but it did not help.  The wiring to the 12 volt
supply and the coil seem to be OK.  Any ideas?  Thanks.  Jim