Aftermarket Rev Counters

[Madmaninshed]

Hi,  My 1900 DG engined water cooled 1986 van has a 2” aftermarket analogue rev counter, fitted by the last owner.  It jumps about, and gives different readings depending on whether accelerating or decelerating (very annoying). There was a similar post on here by someone else who had the same problem a long time ago.  I bought an inexpensive digital replacement, and used the same connections.
The new one is nice and stable, if a little slow to respond. It looks great, but reads almost double (1600RPM at tickover).  The cylinder switch 4,6 or 8 changes the reading on the old analogue one, but does nothing on the new digital one.  Has anyone recently had a similar problem please, and perhaps found a way to get a true steady reading?  The supplier has been very helpful, but has not come up with a solution so far.  Can I check the signal with a multimeter please, and if so, should I set it to volts, amps or ohms please? (Excuse ignorance)
 

[davidoft1]

The switch on the new one is most likely faulty

[The Hairy Camper]

Does the new tachometer come with a trimmer potentiometer for calibration? Looks like a plastic philips head on the back of the tachometer.

If not, you may be better off with a different rev counter. Digital one's probably aren't best suited for our older vans.

[TwinTurbo]

you would need an oscilloscope not a basic multimeter. But the likly hood of the signal being wrong is low as that woul show poor running.