Hour Meters Failed

VOLVO TAMD63 P’s. Hour meters have suddenly stopped working for both engines on both flybridge and cockpit gauges. Tach’s continues to function normally. Any suggestions? This seems to have happened about the same time the start relay failed on the STBD engine. I replaced both start relays. When I noticed the hour meters were not working I put the old start relay back in on the STBD side. Hour meter back up and working, but only on the flybridge gauge. Not the cockpit gauge. Next time I started up, 2 hours later, the meters out again. Not looking like it has anything to do with the start relays. Where to look now?

Bad Ground.
Also check your cable from the brains on the engines to the lower helm. If those cables have a connector that has been wet, ie, hangs down into the bilge where there may have been a high water event, even before your ownership of the boat, the connectors could be corroded.
Now how would I know this?