2nd,
One thing that often gets lost in the conversations, is to remember that the engines, be they M-25s, XP, B series, Atomic 4, - they aren't unique to CTY. So what may 'work' regarding a fuel shut off and tank feed on one boat, may not on a CTY. Also the wiring is basically a Wb decision, not the boat mfgrs. Even though the schematic says "Catalina" the only difference is in the start sequence (Westerbeke panels use the key S-position start, not a push-button start.) So the wiring at the engine is identical, but what that wire connects to at the panel is the difference (S terminal of the key switch, vs the push button.) For the life of me, I can't understand all the hullabaloo of the start system and layout of the panels over the years. Supposedly owners complained about needing to use two hands to start (hold preheat switch, turn key (as on my '84 C-30 panel,) so over the years things evolved thru different systems. The push-button (or key turn) preheat and push button start still takes two hands (or one if you preheat and then let go, so I just don't see the benefit of this. I think it's just like Windows version whatever - being different for different's sake, not because it's better or easier. What's the benefit of turning a key to preheat, versus pushing a button? And pushing a button to crank, versus turning a key? I don't GET IT.
If CTY or Seward wanted to deploy a really top-notch system, they would have used a PTC (push to choke) key switch. Then it's all one-hand operation. Off - Ignition - Start and preheat all on one switch (which is what I will use when I redo my panel.)
On the resistor, what I figured out from the customer's harness and schematic -- and I may be mistaken -- is that the normal flow path (engine running) for the oil alarm is to the preheat I terminal post (via the hot side of the oil switch,) then to ground thru the resistor. That sounds the alarm if pressure goes low. During preheat, the I terminal is hot and so feeds the pump. Thus the need for the resistor, otherwise the oil alarm ground would be a dead short. When preheat is off (running) the I terminal goes hot in the "other direction" (thru the oil switch,) so there is no alarm.
BUT at the same time, there is always a current path to ground thru the resistor while the key switch is in the I position. Doesn't seem to me to be the 'best' solution??!?? A different oil switch -- one that had three terminals - two being a normally open switch (for fuel pump), and the third being a normally closed ground post would be better. Maybe they don't make such an animal, but I would think with Wb's pull, someone could fill the need.
BTW, that 10 amp circuit breaker should be pulled and deep-sixed. It is terrible. Besides that ABYC doesn't allow auto-reset beakers, it's a very poor "automobile engine" component. The harness I just finished - the breaker was so corroded I couldn't get the mounting bar off w/o literally destroying the entire breaker. I found the guts were so corroded that I doubt it would ever have functioned if wire to the fuel pump shorted out. It should be replaced with an moisture-proof ATC or ATM in-line fuse holder. Or a marine breaker.
Cheers,
Ken