Diverse, but limited, successes

As I wrote before, all of the electronics attached to the mizzen mast I had rebuilt malfunctioned when I launched Rune this spring.  After finishing a depressing set of commissioning tests, I set out to repair the electronics, one unit at a time.
I decided that repairing the Raymarine Automatic Identification System (AIS650) should be easy.  Its external unit is a simple antenna, but it still wasn't producing any fixes.  I walked through the six connectors between the receiver and the antenna, and found both an intermittent short and an weak open.  After finishing, I was rewarded by a simple green LED on the front of the machine.
I dismounted the radar scanner between rain showers, and sent it to its birthplace for refurbishment.
Although I find it amazing to learn, the GPS in the AIS650 cannot send its data to the chart plotter. In order to use the C70, I have to replace the Raymarine Raystar 125 GPS that I removed from the mizzen.  Eventually, I shall build a new platform on the  mast; it is really the most sensible place for the GPS sensor.  In the interim, this year, I shall install it on the top of the mushroom vent on the transom.  To firmly affix the GPS without damaging the vent, I shall replace its beautiful bronze lid with a tawdry one of plastic, to which I will bolt the GPS.  Holding the plastic lid onto the vent will be its own problem.
The Raystar 125 is a full GPS system, with its own integrated antenna, receiver, and digital output.  Therefore I shall just connect it to the Seatalk(tm) network when it has been installed.
On Thursday, when I arrived at the boat, I heard the engine alarm bell sounding from the dock!  Since the engine was not running, it was very strange.  To stop the bell, I had to open the main battery disconnect.  I then turned off the engine alarm override, and found that the engine started as it had before.  I concluded that I had partly moved the alarm override switch into its shut (non-override) position when I was in the locker next to it, and that wave action moved it all the way during the night.
The engine started, but not the way it should have.  I had already noted, last year, that the alarm was not operating as expected, and the problem was on the list for later resolution.
When the key is turned to energize the engine, the oil pressure alarm is designed to sound, and then be defeated when the glow plugs are energized.  When the engine starts, and the oil pressure meets its minimum, the oil pressure limit switch closes, and the alarm is kept off.
I found that the positive wire for the alarm circuit was connected on the supply side of the engine switch, rather  than the engine side.  Hence the DC was supplied to the alarm even when the engine was off.  Reconnecting the wire in accordance with the wiring diagram corrected the engine operation.