Challenger 1800 mpem upgraded but one tach does not work

[alkiseadoo]

Had the mpem from my 1997 Challenger upgraded by Westside, installed it today and worked great! Only issue is the starboard tach does not work, port one does. Could this be related to the upgrade or something else?

 

[H€PHÆ$TU$]

I recently replaced both engines in my Sportster 1800. Took about a week of after-hours work. Before I started both tachs worked fine. After I was done, one didn't work any more. I tapped on it and it started working and has worked fine ever since.

Granted, I didn't replace an MPEM, but always try the simple stuff first.

PS: What does an MPEM upgrade do?