Any information will be appreciated.

I have a 1980 (early) F100 351C, however I think it originally had a six
cylinder, when I bought it the tacho was not working and was marked on the
back for 6 cyl, and have since removed it, re-calibrated it for 8 cyl and
bench tested it successfully, however it still did not work when returned to
the dash.

I have spoken to a VDO sales guy who informed me that because I have an
electronic ignition system (after market) the original tach will not work
and needs modification.

If you have experienced this problem and/or completed the modifications,
your information will be very much appreciated. I really don't want install
an after market gauge.

regards,

Stevo