I have a signal generator here, but the Nissan tacho doesn't like this signal either. But my signal generator can only vary frequency and duty-cycle. It cant change the amplitude.

The diesel converter I'm using is is a Dakota Digital DSL-1. The output signal works on my handheld tach/dwell meter.
http://www.dakotadigital.com/index.c...rod/prd128.htm

It has 2 types of outputs .. standard and high voltage. The standard outputs produces a voltage pulse signal from 0 to 12 volts. The high voltage produces 6 to 18 volts -- they told me some tachometers need the extra voltage to trigger. Neither work...

I'll try the variable resistor tonight. Will be good if it works...