First try taking the power plug out of the collector. Check for any bent pins on unit or any plugs that might be pushed back in plug. If all is well there just plug it straight into unit and check. Have worked on a couple with that problem where they were not in collector properly and did not make a good connection. Also check connection at fuse for corrosion and good connection at battery. If it is hooked to a fuse panel run you a dedicated set of wires directly to cranking battery with fuse at battery.
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Charlie Weaver USN/ENC 1965-1979