Ingnition wire to the Alternator exciter connection.
Pictures the harness connection,lower right,the exciter connection for the alternator is above and to the right of the harness connector.
The item center picture is the blocking diode in the exciter circuit. All in the same general area in this case,sometimes its a little harder to find the diode;be-leave me its some where in the harness.
When this diode fails the coach engine may not stop when one turns off the Key. The engine will eventually stop, but in the case of a diesel engine if there is enough voltage back feeding through this diode it may take some time for the fuel supply to drop low enough to starve the engine of fuel.
One can remove and replace a new diode, just seal it up like the OEM connection with shrink tubing and tape. This keeps the connection clean and away from contaminants that will degrade the connections over a relative short time.
Should is diode become open,the Alternator will not put out any voltage / Not charging batteries.