tachometer question
 

Hi everyone,

I've got a tachometer question. Finally got the project running after a year and now the tach is erradic...

At motor idle it is reading 2300-2500rpm.. it moves when the motor is reved, but it swings and bounces and is not smooth or accurate...

What should I check firsts?

details: motor is stock ignition, and ran fine with a working tach one year ago in another chassis (72)... Tach is stock and worked fine with another motor one year ago (74)..
plug wires are not new but look good.

anything is possible and I'll check the wiring again. also of the 3 terminals in the back of the tach, does the black/purple go on the end terminal or in the middle terminal?

thanks everyone
brant

From my experience the tach is very 'picky' in its requirements to have the correct waveform coming off the coil. So make sure the points and condensor are in good working order and the coil is wired correctly. Going by memory the black/purple wire goes to the middle terminal on the tach (the other two are +12v and GND) and the other end of that wire goes to the neg. terminal of the coil which also connects to the points.

Accoarding to the wiring diagram (which i have become quite familiar with LOL) If looking at the gauge from the back there are 2 leads side by side on the top 2 leads across the center, one on each side and one on the bottom in the center.

2 leads on top are turn signals wires (Black/Green, Black/white)

Center of the gauge on the left and right are black/blue and both seem to be lights.

the last lead on the bottom of the gauge in the center is white/blue and that runs back to the fuse panel, fuse (1).

This information was from the wiring diagram up to 1971 USA models.

Other years don't seem to be any different.

Hope this helps.

Luke

One of mine 914's did this once when the point gap was way off. Check the dwell. It the points and condensor are old, replace them.

Regards,
Daris

thanks guys... sounds like I'll be checking points tonight or soon....
(just to be safe I'll double check the wiring on the tach too)....
its weird that the same coil/motor/distributor, and points worked fine with the tach in the other shell... but I suppose just dropping the motor and reinstalling it could have bounced things around or caused them to change...

car runs pretty good, but does feel a little down on power so I suppose it could be off....
points were new 3000 miles ago, but could have worn in and need attention I suppose...

b