Ya this is a diesel web site, but sometimes we get gasser questions that throw us for a loop.
Cluster? That's why I asked, if you hit the dash and it begins to work, question. Some times it is the simple things.
I'll take a look at the schematic tomorrow to see how it gets it's feed. Others will chime in if they know.
OK I learned something today, your Tach is controled by the alternator (white wire, cavity A). Check the white wire for short to ground, open or short to hot. If that is ok then, with alt connected, engine running, cluster removed check voltage at cavity '6'-cluster connection. 'Observe for potentially pulsating voltage at or below 14 volts'
voltage present- Replace cluster
voltage is NOT present- Replace alternator
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