I haven't been able to come up with a definite answer, but I do have some suggestions. First, remove the tach and look on the back for an adjustment control or switch. It could be behind a small hole in a metal rear cover.
There could be a plug-in circuit board on the back of the cluster. Look on that for a switch or adjustment.
A number of years ago I was asked to repair a factory tach from a 1970 Plymouth Superbird. I needed a schematic diagram, and the only way to get one was to draw it up myself. The circuit board only had 20 parts. It was a very simple circuit and it ended up having a wire that could be moved to a different location for different engines.
Other than those things, I haven't heard from anyone who said there are different tachs for different engines.
Saturday, March 27th, 2010 AT 2:11 AM