1972 P1800ES Tachometer connection

[Grahamwhitfield]

Does anyone know where the two wires connect on the coil and distributor?

I have the coloured wiring diagram but they only states that one goes to coil and one to distrubutor. Not where on each they connect. (Diagram attached)

any help would be appreciated.

[Ron Kwas]

Graham;

Welcome to this forum!

A '72E will have a Gen3 Smiths Tach, with internal Inductive pick-up coil. Connected as seen here:

Source: https://www.sw-em.com/Smith's%20Tach...s_Gen2_vs_Gen3

Good Hunting from Connecticut!

[Grahamwhitfield]

Thanks Ron

Still finding my way around here.

It is the same one you sent the link for thank you. Yes the red/white wires are attached to the rear of the tach as pictured.

However, following the other ends, I have traced them to the engine bay but they are just wrapped up and not connected to anything (explains why the tach doesn’t work!)

I know one goes to the distributor and the other to the coil, but I don’t know where on them they should be connected?

[Ron Kwas]

Graham;

Connections are as on the wiring diagram you show...Red to Ign Coil Neg term, Wht to Points terminal.

Cheers

[142 Guy]

Before connecting the red and white wires to the appropriate terminals, use a multi meter to check the resistance of the electrical path through the tachometer circuit. It should effectively look like a dead short (very low resistance).

There may be a reason that the wires to the tach have been disconnected. An open circuit or high resistance indicating a problem inside the tach will kill the ignition system and a previous owner may have just by-passed the tach circuit to enable engine operation rather than spend the money to repair the tach.

[Grahamwhitfield]

So basically the two connectors should have a virtually no resistance between the red and white wires. Assuming it’s really the same wire that goes inside the tach, wound around inside then back out again?

Will check this and let you know.

[Derek UK]

I would guess that you have a wire running directly from the dizzy to the coil. The low tension wire. The engine wouldn't run otherwise. As an example this is how the Amazon with no tach is wired. The tach wire replaces this and allows the tach to count the pulses.

[142 Guy]

Originally Posted by Grahamwhitfield

So basically the two connectors should have a virtually no resistance between the red and white wires. Assuming it’s really the same wire that goes inside the tach, wound around inside then back out again?

Will check this and let you know.

Correct. Actually wound around a few times to form a current transformer; but, that is being academic.

Heed Derek UK's advice that if the engine runs somebody has inserted a by-pass between the coil negative terminal and the connection to the points on the distributor. If you want to try connecting the tach you will have to remove that by-pass and replace it with the tach connection.

[Grahamwhitfield]

Sorry for the late replies I have been waiting for some drier weather, which I don’t think is anytime soon.

Anyway, I have managed to test the resistance between the tach connectors and it reads 0.1 ohms and on a buzz test it bleeps like a short circuit. Which I think is right as it’s basically one continuous cable looped around inside the tach.

I have also attached a picture of the back of the coil. Where the black and red wires go inside the distributor cap. I assume I can just disconnect the black wire from the coil and connect it to the tach and then from the tach to the connector on the coil I just disconnected?

[Mike Arnold]

As an aside, once you have got the tacho working you may find there is more interference on the radio. Bringing the points-coil wire inside the cabin can introduce a bit of RF noise.