Over the last 5 or so years I have encountered this intermittent problem.
With a new engine totally rewired by me and all new panel and wiring I assumed the problem was solved.
However, it was not. I found that Amel used welding wire and not tinned wire from the starting battery and the main switches. Additionally , the lugs that they used were open at the terminal end. Thus, allowing the battery acid laden air to enter the wire, When I cut the wire open, I found that it was corroded for almost 2 feet from the battery.-which causes a lot of resistance . The voltage at the starter motor was + or – 11 volts.
The Valeo solenoid is rather sensitive to low voltage.
Upon further inspection of the cabled from the starting battery to the vapor barrier connector was a completely different color than the wire outside the battery box.
I replaced the cables and used closed end connectors on the cables. I also soldered the cables to the connectors after crimping them. I then applied Scotchcote,
which is used on many underground connections.
Now the engine starts and stops like a charm. I also noted that the generator starts much more quickly.
While I was in the battery box, I noted that the common lugs posts for all the batteries were somewhat corroded. I loosened the nuts and applied corrosion x in between the lugs. My next project is to replace all the battery cables.
Kimberlite Amel Super Maramu #376