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620 tach problems'

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A few month's ago a fusible link fried in the engine compartment(coming from the battery). Searched all over and nothing else was visually wrong, so the link got replaced and I went on my way. That night, I noticed a dash light out in the tach gauge spot. The next day, I noticed that the tach it self was working funny...Ignition off or on(non-running engine): tach reads Zero like normal.. but when the engine is running, the tach reads 3600-4000 at idle and 5000-5700 depending on the actual RPM. Only have a swing of about 2000 RPM on the gauge itself, all of which happens with the needle reading over 3500 the whole time..


Could the bulb out be a grounding problem in the tach? Are there more fusible links under the dash??

(but wouldn't a burnt link or dash light out cause more problems than a weird tach?)

Wiring and I aren't exactly the best of friends but the problem need to be fixed...any help would be appreciated

Thanks, RustyRat

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This is a factory tach... the needle position is a little different than I described I guess, but not by much..



No key on; needle at zero.. key on, engine not running; needle at 3000...running at idle 3000-3400 RPM...anywhere in the driving range 4300-5300 depending on what electronics are on..heater on; needle drops by 200-300 rpm, same with the lights; 200-300 rpm lower when on.. blinker on; needle dips 200-300 with each time the relay activates

Buddy at work said something about a ground, but I'm wondering why more not F---ed up by this if it is a ground problem..



Cases like mine are probably why those electrical shops love people like me...


Thanks, RustyRat

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Have you tried wiring the tach direct to see if it's not screwed up? (not through your wiring harness)

I have thought about that, but haven't done it yet...partly because I have no idea how to remove the dash and gauge set. When I find out how, I plan on some tunes at least to take my attn away from the other things I could do to make the 620 better, for a little while anyway. Always something to do to it, seems like never ending project..

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Check your points. File and gap them. Tighten all connections inside the dizzy. I always new when my Dart needed new points... the tach would jump around slightly.


Just recently,RisingSun had an add for 'Datsun Parts', I picked up the remote dizzy and finally got on the 'EI Dizzy' train, so to speak..and still the tach problem is there. I know how to drive with out a tach but it's stock, it's there, and it once worked before the fusible link burnt out, so it's just bugging me to fix it.. I installed the new EI dizzy between rain squalls one day last weekend(late X-mas present for myself). It was out of a '78 620 W/Manual so the dist #'s show from Jason Greys' FAQ for EI dizzys'/dizzy spec..shows for 12deg BTDC at idle and that's where it's at (haven't played around W/timing yet to see how much I can run, but that's a different days' playtime.)

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