I've had this Jensen-built sex machine for nearly three years and I think it's finally time to get the tach working. It's never worked before but I suspect it was disconnected when the PO installed an ignition booster which I've since disabled (and it didn't make a difference). The needle on the gauge will occasionally bounce if I turn on something electrical or even light up the brake lights, but it doesn't do a thing beyond that. How should it be wired to the coil on this model?

Ben

Ben,
George is correct in saying that there are different methods that different tachs are wired. To sum it up, there are two different ways that they are wired. Series and parallel. My P1800E uses The Smiths tacho,(1970) which is wired in series, ie all the current flowing through the low tension side of the coil goes through the tacho- 4 amperes worth and the wire is pretty hefty to handle this current. There is a small coil that this current flows through inside the tach which induces a voltage that the Tach uses to signal rpm and since it is in series , unplugging the tach connection at the coil will kill the engine . There are other wires that power it. I can't remember off hand how many.
Your 63 model will probably use the same system.there should be a wire going to the coil and one coming from it. You should interpose these two between the CB side of the coil connection post but you should get the polarity correct. I am using a contact assisted electronic ignition system that I designed myself and wiring the tacho in series has caused no problems so far, (The primary current must be in the region of 5.5 or so)

The other variety uses voltage and a small wire tapping off of the CB side of the coil. THis type uses voltage instead of current to run it and is much simpler to wire. If you are adding one then go for this type. There should be enclosed instructions as to how it should be connected.

Remember to get one for four cylinders as the reading will be wrong if you get those meant for 6 or 8 cylinders.

Good luck

I'm not an expert on either 1800s or tachs, but....
They usually read electrical pulses and count and integrate them.
Normally they are connected somewhere between the distributor
and the coil negative (the wire that runs from the coil to the
distributor). Many also require a 12 volt connection for power.
Some have a third connection that should go to the panel lights
if they have a light inside them.

I understand some are coupled inductively to the ignition system
and just have a wire that coils around one of the connections to
the ignition. Sorry I can't furnish more specifics.
--
George Downs, Bartlesville, Oklahoma, Central US