Tach problem 1980 308 GTSi

Update on request for help with tach cutting out often but without clear pattern. Thank you very much for advice to switch modules to isolate problem. One of the connections was not fully clipped/locked into place. The rubber boot prevented the connector from disconnecting completely, but apparently allowed slight movement back and forth.Have driven quite often over the past month with no problem at all. Trips are getting longer as I do believe the culprit has been found. Again,Thank You ! My only regret is that I did not post sooner.
Cheers!