depends on the ignition system you are running, if it is an MSD you will need the Tach adaptor. Take a look at the post started by "COZ" started 12-12-2001 under the headine "TACH NOT WORKING". Also do a search on this site under "TACH" & "MSD". There have been numerous discussions on this topic and you may find it helpful.
Good luck
Gary #06984
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