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MG MGB GT V8 Factory Originals Technical - Using stock 77 tach with GM DIS

I am having some difficulty getting any electronic MGB tachs to operate with the GM DIS ( direct ignition system). I've already tried the ordinary modifications that were suggested in the archives. I can make any of them work with a distributor, electronic or mechanical, or with a freq. generator. I suspect I might be experiencing to much or to little amplitude in the tach drive signal from the DIS or it's possible the signal is current based. I sold my Oscilloscope (kicking myself now) and am in the dark on this one.I have corresponded with Mark Olson and tried his suggestions. Does anyone have any other suggestions they can share. It certainly would be appreciated.

Dann BCC
Dann Wade

hello dan, i used my stock tach on my 1978 and had the DIS on my 3.4L, i sent my tach in to APT insturments in bloomington, mn and they adapted it to the engine, not an advertisement for them and sorry i do not know exactly what they did but it cost me about $175.00, however it worked good for a couple years and i have now removed it and changed gauges, and sorry but i sold these off already.
james madson

James, thanks for the info. I'll do a web search and contact them.
Dann Wade

When I added an MSD probillet distributor and 6 AL box I had a similar problem and had to add an MSD Tac Adaptor. Perhaps you could contact MSD tech support and see if their Tac Adaptor would work in your situation. Their Adaptor is only about $40.00 or less.
Michael S. Domanowski

Michael, that is a very good idea. I will do so. Thanks very much.
Dann Wade

Hi Dann,
APT Instrument can be found at:

They will not tell you exactly what they do if you asked them, but they do it. Basically, they place modern electronics inside your old Smiths gauges and leave the standard Smiths hookups. We have had them do tachometers for Electromotive DIS systems as well as GM DIS systems and found that both need these alterations... The tachs work perfectly.

BMC Brian McCullough

This thread was discussed between 28/06/2004 and 30/06/2004

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