Tachometer not working

[TimBarb]

81 Formula. Finally got the new engine installed and car back on the road. Working on getting some other items sorted out/working. Having problem with tachometer. Tac is doing nothing once car is started…… just stays at zero with no needle movement at all. Noticed that when I’m cranking to start engine, the tac needle reflects the rpm’s during the cranking, but nothing after that. Looking for advice regarding where to start and troubleshoot the problem. Appreciate all the help . Thanks to all!

[Wallington]

The tacho is an easy one to test outside of the main engine harness, other than having removed from dash or access to the rear. One wire goes to a live source, the other to the Tach plug on the distributor. That rules out all the other harness and potential issues. The fact it moves when cranking shows it is at least getting signal of some sort, whatever that means. The signal is either lost when not cranking or something else is running through it.

Circuit boards are available for this type, reproduction tachos are not. The large semi-circle type half the size of gauge face is the type used for the Quartz clock/tachs, but that's last resort.

https://www.thepartguy.com/images/products/gauges/6K(80-81)Tach-4.JPG

https://static.wixstatic.com/media/9fd292_5081c4b3ae854d30a7c93b56d8a02a27~mv2.jpg/v1/fill/w_520,h_444,al_c,q_80,usm_0.66_1.00_0.01,enc_auto/9fd292_5081c4b3ae854d30a7c93b56d8a02a27~mv2.jpg

[TimBarb]

Thank You Wallington.

[b_hill_86]

Test your signal wire coming to the gauge with a test light. It should flash with the engine running. You should have a pink and white wire I believe (may depend on year). It would be the white.

[TimBarb]

Thanks Brian.

[TA301]

Thanks Brian.

Remove the tach and make sure the tow nits on the reverse side are tight.

[TimBarb]

Thanks TA301

[79 Moneypit]

Make sure the pink wire to the tach (power) is hot in run.  It sounds like it could be hot in crank only.

[TimBarb]

Thanks 79 Moneypit