problem with defi rpm gauge

[Bean]

if you don't/can't use the NE signal the IGF would be next to try... this is the confirmation signal from the igniter to the ECU.

have a good read here: http://www.autoshop101.com/forms/h23.pdf
(diagram on page 6 is the OEM AE86 setup)
and also have a good read of the Defi manual to check what it wants to see.

PS: what model tach do you have partnumber - iirc they have usually two different input wires depending on the signal you supply.