The V8 Owners Forum -

I just bought myself a matching truimph Stag 100mm tacho and speedo. I attached the tacho. Simple enough! Worked fine! Then the car electrics gave up after a few miles. Suspected the lumenition so disconnected and returned to points and coil. All seemd well until i came to reconnect the tacho. The engine wouldn't start at all with it connected and if I tried when engine going it began to stall. So maybe my lumenition worked or got fried by the tacho.
So, three terminals on the back. An obvious earth one and the two together ( one being a bullet type ) This latter one I determined to be the trigger and so atteched to the -tive coil, the other to a switched live on the ignition. Does anyone have any suggestions if I may have done something amiss, or know what to do to test the tacho?
Help would be appreciated as I don't fancy frying another lumi.
Thanks

If this is the original then it could be that it works on current sensing and not a pulse like modern tacho's. You break the wire going to the + on the coil and run it through the tacho.