Converting a Positive Earth Tacho

to Negative Earth

Remove the tachometer by undoing the two knurled nuts and taking off the lock washers etc. and pull it out of the dash. The wire loop that runs through the post on the back of the tachometer needs its direction reversing; mark one side of the loop twice a few inches from the tachometer and then cut the wire between these marks. Cut the wire on the other side of the post, again a few inches from the tacho' and attach connectors to all four exposed wire ends. This allows the connections to be swapped over thereby reversing the direction of the wire loop. The point of making the two marks is that when connected correctly for negative earth you should have one mark on the wire loop on either side of the terminal post.

Reversing The Tachometer Loop

Disconnect the tacho' and remove it from the car. Carefully loosen the chrome bezel of the tacho' around its circumference with a small screwdriver. Once loosened, grip the bezel and turn it until the lugs on the bezel line up with the cut outs in the tacho' body, then remove the bezel. Remove the two screws from the back of the tacho' and the internal assembly can be withdrawn.

Examine the internals of the tacho' : you will see the connections to the external spade terminal and post. These connections have to be swapped. The resistor connected to the spade terminal must be un-soldered and connected to the post immediately to its left, and the wire previously connected to this post should be connected to the spade terminal to which the resistor was originally connected. Re-assemble the tacho' and fit it back to the car ensuring that the loop is set for negative earth as described above.