I know people will say just get a multimeter that’s does it, but..... Will this do the job on the breakerless electronic ignition bus? https://www.drapertools.com/product/79005/Automotive-Tachometer
It ,s inductive - so it looks like it senses the current in the ignition cables - so just place it near the HT lead on the dizzy
It will work. Its a pity Maplins went belly up - the automotive DMM i use is the UNI-T UT107 bought in Maplins about £20 but only from China/HK. ( it was £30 in Maplins) . That does the same as the Draper and other measurements too. If I were buying a tachometer specifically I would get a contactless laser tachometer as that will be useful measuring other rotating machines not just engines. Sticker on a pulley or shaft, you can measure it.
