Toyota 4WD Surf Owners

Alright guys I need a hand this thing is doing my head in.

I had a diesel engine and tacho in previously.

Ive swapped it for 3UZ-FE 4.3L V8 and as far as I know the ecu outputs a 5V square wave signal for tach.

I got a petrol tacho and a signal booster to convert the 5v square wave to a high voltage pulse and feed the wire to the tacho.

Turn the key on, engine off and the tacho shoots straight to 3200 and just sits there regardless if the engine starts revs etc doesnt do anything til I turn everything off.

Have I got wrong signal? It's hard to check without an oscilloscope which i cant get my hands on. Have I got the wrong tacho? It counts to 8000 rpm and has the potentiometer on it for adjustments which ive played with and did nothing. Could it be wrong terminals on the gauge? Its pretty hard to stuff this up as their shared with other things in the cluster and everything else works so I thinking it might be something signal wise.

Side note - My power steering fittings keep leaking in the box itself. Ive tried using copper bushes etc but they still leak, anyone got any hot tips for young players?