Q: After installing electronic ignition system, I cannot get tachomter to read RPM. It is dead. 1975 Mercedes 450SLC

asked by on March 16, 2017

AFTER INSTALLING ELECTRONIC IGNITION SYSTEM, I CANNOT GET TACHOMETER TO READ RPMS. IT IS DEAD

Hi there - there are a couple of possibilities for this problem. Worst case is that during the ignition modification, the tachometer was somehow shorted, and is not non-functional. More likely is a lack of the proper "trigger" path from the distributor to both the fuel injection/ignition system, then on to the tachometer (it’s the last component in the path). The solution here depends on how much of the ignition system was replaced, and what it was replaced with. Most, if not all, of the aftermarket ignition systems provide a tachometer trigger "output" for just this function. There are sometimes electrical mismatches (e.g. need for a resistor) or pulse dividers to get the correct trigger counts to match RPM. Check with whoever you bought your replacement ignition system from, or the support desk/web site of the manufacturer of the ignition gear for assistance.

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