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TR4/4A Coil - easily confused...


Senior Member
Hi all,
I have a '64 TR4. I have converted it to negative earth/ground. This involved switching the wires to the coil.
I now want to wire up my (converted to electronic) tach. One wire runs to the "negative side of the coil".
Having swapped wires, I am now confused as to which side this is!
Can someone clarify for me - many thanks.


Luke Skywalker
Country flag
Since you moved the wires around, it doesn't make any difference what the coil says. Put your volt meter onto the wire that does not go directly to the distributor with the ign on. It should read + 12 volts more or less (-12 before you moved the wires). Connect the tach to the other side of the coil which is now now negative.

Geo Hahn

Country flag
That may work - but I'm thinking on some coils there was also something (a loop of wire?) that had to be flipped when polarity was changed.

I'll confess I have limited experience with electronic tachs and none with how they handle a polarity switch.


The short answer is that for a later (modern) voltage pulse sensing tachs on a negative ground car, the tach wire that is connected to coil negative connects to the coil terminal which also has the white/black wire going to the distributor.

The "loop" wire was for the old RVI tachs. They are generally not compatible with electronic ignitions. The loop wire basically replaces the white/black wire going between the coil and distributor (2 wires to the ignition system, not one).


Senior Member
Thanks guys.
I have no loop wire and I simply reversed the 2 wires on negative earth conversion.
The white/black now goes to the distributor, the solid white disappears into the loom and I assume therefore back to the ignition switch.
The white/black connects to the coil at the terminal marked " - " so thats the one I'm connecting my tach to.
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