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MG MGA - Elecrtonic Tachometer

My mechanical tacho been playing up and may need to go off to a specialist for repair. A friend has offerred me an electronic impulse tacho in the interim (positive earth) and would like to wire it up and it seems fairly straight forward BUT the electronic tacho he thinks is missing a metal cover that goes over the nylon block at the back through which a white wire is looped. There is a small screw and nut that goes through the nylon block and 2 short metal tabs just protruding from the back cover each side of the block. My question for those up in this sort of thing is whether the metal metal cover is doing anything other than securing the nylon block if not there's a chance it might work?
J H Cole

No it won't work without the metal tab. It works with a coil of wire around the nylon, which creates a pulse in the metal tab. The metal tab is a flat U shape and works like a staple through the nylon and into the slots each side of the securing screw.

The good news is that it's very easy to make the tab out of a piece of a (steel) scrap - I made one for someone last year. Just trim it small enough to go through the nylon and into the slots.

Also note that the thing doesn't work if the wire coil is connected the wrong direction, so just reverse the connections if it doesn't work.

But there's been a few rapturous recommendations for a man in Redditch (either here or on the midget board ) who does a super job with an amazing turnaround time so maybe it's easier just to get the original repaired by him now instead of messing around with the impulse tach

dominic clancy

If you need to borrow one of the metal tabs as a pattern let me know.
John Bray

Thanks for the input Dominic and the attached picture shows the back of the tacho and the nylon block that I now understand is missing the metal tab. Thanks also John for the offer that I'd like to accept for a pattern if it's a simple piece of steel fashioned to a bent shape. Can you email me on and we can sort details out.

J H Cole

On the off chance that you have an electronic ignition (pertronix, etc.) the electronic MGA tach may not work in your car.
F. J. Bruns

I believe this is the part you need. I have sent you an email

John Bray

As FJ pointed out, if you have a recent (within 4 years) electronic ignition, and negative ground, your positive ground impulse tach will not work - you will need to have your tach rebuilt with modern internals. Around $250.00 US but worth it.
Bayard DeNoie

Is it all worth the effort? By the time you have sourced the bits your mechanical tachometer will be back. Mine was turned round in a week back in 1997.

Steve Gyles

The guy in Redditch apparently does a next day service for less than the price of the normal service from other repairers.
dominic clancy

The repairers I contacted all wanted to overhaul the tacho for around 80 but not sell a missing part. I've met this problem before when it comes to instruments, spare parts are difficult to get hold of and it tends to be an overhaul or nothing. Did not know of Richard Jenkins but understand he's on holiday at present but with thanks to John Bray I've
fabricated the small metal cap and tacho is now working.
J H Cole

This thread was discussed between 30/09/2015 and 03/10/2015

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This thread is from the archive. The Live MG MGA BBS is active now.