Tacho Connections

[bcmc33]

A simple question which won't save my blushes, I know - but what wires go to the two bullet connections?

I just hope the tacho isn't sh@gged.

[types26/36]

Its a little hard to read but I'm sure you can if you view full size
http://images.google.co.uk/imgres?imgur ... N%26um%3D1

[Bruce Crowthorne]

Crikey it's not often I get an answer in first

These are the connectors for the current trigger wire.
From memory they are both white, polarity doesn't matter so just go with the sex of the connectors.

One end is from the ignition switch (probably via the anti theft switch in the glove box) and the other end goes to the coil.

Hope this helps
Bruce

[bcmc33]

Thank's guys.

I was a little confused as both wires were white.

I am currently setting-up a fuel injection conversion and have a "little" problem with the tacho reading four times the engine speed. I guess it's something to do with the DIS ignitions system.

I shall talk with Speedy Cables tomorrow, maybe they have a simple solution without modifying the tacho.

I shall keep you informed.

[john.p.clegg]

Brian

Do you not have a setting in the Tach out on your EFI?

John

[bcmc33]

John,

The tacho adjustment in the ECU software does not change the situation. The ECU supplier says a seperate 'magic' box can be made to cure this rarely seen problem.

I shall talk to Speedy Cables to see what they have to say.

[Bruce Crowthorne]

I think you will find that you will either have to have your rev counter modified to take a "voltage" trigger and not the existing current trigger, or replace the unit completely.

Your existing unit needs the fairly heavy current of the coil firing circuit to trigger it to work.
I am pretty sure that no such feed will exist with an EFI setup!
It didn't exist with my Aldon electronic ignition.

I ended up having mine modified to a voltage triggered unit.
Later rev counters are voltage triggered (mine is a 1969 car) but there is a script on the rev counter face which indicates if it is current or volatge triggered. Can't remember the exact letters but the current triigered ones have something ending in "I" (it may be RVI?).

I had mine done by a guy called JDO Instrument engineers, but I wasn't awfully happy with the job he did. It works - but it is under damped and the quality of the metal working (it needs a hole cut in the back of the case) is poor.

Hope this helps
Bruce

[john.p.clegg]

Bruce/Brian
Sorry,didn't notice that you have an older current fired tacho,yes, you will need to upgrade to a voltage driven one...these can be picked up quite cheap at autojumbles and either used as is or re-fitted into your case...or you could have Speedy Cables do the conversion (good company)

John

Re-looking at your photo,I seem to remember my old tacho had two white wires "wrapped" round an inductive bridge? Are you sure it's not a later voltage driven thingy??

[alan71]

The later type of tacho has the loop of cable round the transformer inside the case.

Alan.

[Bruce Crowthorne]

I think the "loop" version was just the earlier version of the same thing.
B

[alan71]

I should have made it clear what I meant by later type, it?s still current sensing but you can?t see the loop of the white ignition cable as it?s inside the case.

Also the circuit's different, it does it all with one transistor.

Alan.