Jaguar Repair: E type tachometer not working

Question
Hello Howard
Just found this site and it looks very informative.
I recently brought a 1970 E type from the States to the UK, the tachometer is not working and the contact breakers have been replaced with an Ignitor electronic unit. The two new wires coming from the distributor have been connected to the new coil with one white wire from the original harness also connected to the +ve side of the coil.

There is a second white wire from the harness which has been left disconnected (presumably from the distributor?). Does this appear to have been wired correctly and if so why is the tachometer not working? I do not want to change anything as I am concerned about blowing the tachometer.

Any advice gratefully received.
Tonyls5ej

Answer
Hi Tony,

I worked on the E-Type from the first to the last but can't remember what year they changed the type of tach. The eariler tachs worked off of a tach generator mounted on the back end of the intake cam. If there is no generator there, then the 70 model had the tack pick up the signal from the ignition.

I believe your car is a series II 4.2 so it had the tach that was triggered by the coil. The way it was wired was that the #7 fuse powered the coil but went through the tach first then on to the coil and on to the distributor. The wire from the coil to the distributor was white w/black tracer.

The E-Type had a lot of white wires from fuse 6 and 7 and only meant that they were powered with Ignition ON. Not like other British cars where a White wire was an Ignition wire.

Your tach should be powered by a green wire from #7 fuse but have the power for the coil run through the tach.

The problem is that many aftermarket electronic ignition systems use low voltage (6 volt) coils and that may be why the tach don't work. Or they rewired the ignition wires so that the power to the coil no longer runs through the tach.

Here is what I would do. Pull the tach out with its wires still attached so you can see the two white wires on the tach and then test the wires to see what wire they go to near the coil.

My diagram shows the #7 fuse runs a white wire to the tach and a wite wire leaves the tack and goes to the coil as a power (Ignition ON) wire for the coil.

Most all electronic ignition systems just ground the coil jsut as points did it. But it usually required more wires to do it. They usually required an additional power wire to power the igniter as well as a power for the coil.

If your system is using a 6 volt coil, you may need to put a resistor in the wire that runs from the tach to the coil as a 6 volt coil will over heat and burn up with 12 volts applied to it.

Howard