i looked into the "impulse sender" plug, and found mine had come loose, which is why the tach would work once in a while... i took it out, cleaned the leads a bit though they were pretty good, and folded up a piece of paper and stuck it into the top of the plastic housing cylinder for the plug...the filled up the extra space, and the tach works now 100% of the time... a better idea would probbably be to put some kind of rubber in there instead, but the paper should be alright for a while