I like my Koolaid too, but not mixed with my electricity

[KWKloeber]

Some additional (incorrect, non factual) arguments why the OEM preheat circuit is "bad." 
[With the incorrect "facts" corrected]:

"..the current must travel in a #16 gage wire.."
The preheat circuit is 10 awg and has always been 10 awg.

"...the voltage at #3 cylinder... must be only a dribble.  "
The voltage drop is 1.2 v over 32 feet (16' up/16' back) with (3) 6 amp glowplugs.
Newer plugs *reportedly* draw about 9a each. That's 1.6v drop over 32 feet.
Not a "dribble" at all, it gets the voltage closer to (a little bit above ) what the GPs are designed for.

"Why NOT [do the MOD] !?!"
Here's ONE reason:

February 13, 2017
Subject: NGK Y-103V glow plug question
To: [me]
Hello,
Thank you for your inquiry. It will definitely damage the glow plug by putting direct battery voltage to it. There is a resistor in the controller box so the glow plug only receives 10.5V. [NGK's referring to the Kubota tractor preheat circuit - k]
NGK

"...never measured the voltage at #3 cylinder..."
I have, and the drop was consistent with above.

"... that dribble must ... energize the next 2 plugs"
There's about 0.02v drop in 6" of wire, so plug to plug the voltage is identical by any measurable means that we have.  There's no drop GP to GP due to the GPs themselves (such as if they were wired in series.)
However, that's a good point -- it makes sense to feed to the #2 cyl, then split to #1 / #3 GP.

"...the Ford truck solenoid mod. will allow you to just open a circuit (for 2/3 seconds)"
First, there's NO WAY on this Earth that a proper, maintained, preheat circuit takes 30 seconds that the mod can reduce to 2-3 seconds.  If so, then something was drastically wrong with the OEM preheat wiring before the mod and so not a fair comparison.  The mod shortens preheat by between 10-15 seconds, depending on temperature.  To be fair, lets just say it cuts the time in half.

"...Why energize that circuit for 30 some seconds (dragging down the battery/s starting power)..."
It takes "X" amount of energy to heat the glow plug -- more seconds @ lower volts and amps OR fewer seconds @ higher volts and amps.  The difference between the mod/no mod is 0.05 amp-hr. Insignificant. 
Likewise, the total energy to preheat is insignificant (between about 0.1 and 0.2 amp-hr.)
Additionally, introducing a Ford solenoid (meant to handle STARTING amps) draws another 1-2 amps from the battery that isn't required if you leave the OEM circuit as-is.

"...the old original charging circuit thru the gummy plugs was bad ... why would you do the same with the glow plugs?"
Because that's arguing Koolaid and Gatoraid.  Apples/oranges.  Different animals.  A strawman argument.
No one is suggesting that the preheat go thru a plug.  A classic strawman argument!

Second, we know the differences between charge and preheat -- anyone well versed about harness issues knows that they had nothing to do with the preheat circuit.  Nevetheless, info for uninformed owners:
The key to the harness was the PLUG itself and the resulting fire hazard from:
     * CONTINUOUS high charge current from the alt. (not much lower, intermittent, preheating.)
     * Corrosion at the plug heating/expanding/burning contacts and adding more corrosion/resistance, and finally melting the plug -- and the resulting fire hazard.
     * The drop in voltage and inefficient charging.

Leaving the GP circuit as OEM has nothing to do with those issues.  Read again above from NGK, why you WANT a voltage drop in the original GP circuit and NOT put 12-1/2 or possibly 14-1/2 volts (from a shore charger) to them. 
That's the absolute opposite of the concern/problem with the charge circuit running up to the cockpit.

When we tried to start the engine, nothing happened.  I knew exactly what it was, because ten years earlier I had replaced the start button to starter solenoid fuse holder, and had since relocated it to a more accessible spot (see Critical Upgrades).  I hopped down below, opened the engine compartment and messed with the fuse holder, and asked Morgan to try to start the engine.  It turned over this time, but didn't start because it was cold.  By then those large racing sailboats were bearing down on us, having slid out of the dead zone and hit the breeze.  We could see the bones in their teeth, a few heading right for us.

I told Morgan to hit the glow plug button for 12-15 seconds, and then the engine started right up.  And we motored out of their way, close call.

Do I mind being able to start my engine faster?  No.
Do I need it all the time?  No.
Do I appreciate having it.  You betcha.

Of course, the question is not whether one has the right to YBYC or not. Of course everyone does.
The question is -- if critically thinking about it -- does it make sense?  To some it always will, no matter the facts.  To some the facts outweigh the potential 10-second time saving.  C'mon men n ladies - TEN SECONDS.  Really think about that.  Ten WHOLE seconds.   Now let it sink in. 

It's not (just) dem glo plugs. Yes, shortening the preheat time does (somewhat but not in every instance) counteract the higher voltage.  But, there's also the case where you're putting not just 12v to a 10v plug, but putting 14.5v to 10v plugs.

If that's acceptable to some -- great so be it if one wants to do it -- YBYC -- but it doesn't automatically transform it into being a smart idea when critically thinking and weighing the facts, not the emotion over it (a hot glo plug button issue, so to speak.)  Some get defensive because they have done something or installed something, that maybe wasn't deadly, but maybe also was not the best move.  I've done "not the best move" many times, but learn from it instead of defending it.  Some were doozies, but again it doesn't automatically transform them onto a good move just because I had decided to do it.

If the life/death situation comes down to me being north or south of 15 seconds, d'yah think there's potentially something else wrong?  Like me not being prepared, or me simply being reckless about the location I was approaching?  (What I forgot, this breakwall just popped up on me?)  Or like me forgetting to start the engine well ahead of time if there's a potential that I may need it, rather than me waiting until life/death depends on 10 seconds vs 20 seconds of preheat.

We ought not lose sight of the FACT that, given a choice, we ought to make systems LESS complicated on a boat, not MORE complicated when it's absolutely, positively unnecessary (an only a "niceity") to do so.  That's not just an opinion that's a GOOD idea on a boat.  Relays and solenoids do fail -- infinitely more often if I install unnecessary ones compared to when I don't install unnecessary ones.  Connections do corrode - infinitely more often when I install unnecessary ones than when I don't install unnecessary ones.

Murphy stows away each and every time each one of us goes out.
What's more simple than a fuseholder?  If that fails and puts me in a life/death situation that relies on 10 seconds to get out of, what about a different, more complicated (and totally unnecessary) component failing?  That can never happen to me?  Until it happens, of course.  Murphy.  We all know him. 

A failure like that speaks more to the installation or the part I used, than having a fallback 10-second savior to a fuse holder failing.  That's akin to me justifying to myself to carry 10 gals of explosion in my trunk just for the happenstance that I will be thankful when I didn't start with tankfull that I had the gas can to fall back on.  Or if my fuel gauge goes haywire.  Or I "forgot" that I was going to drive thru the desert and "forgot" to fill up.  Yes, at some obsure point in my life I might be glad that I carried that tank, and I could use that to justify it to myself if someone said to me, "Yah know, that's not a great idea, but it's your car, your choice."

I've seen three preheat solenoids fail on the B engines, and they weren't abused.

If using a relay, it has small quick-disconnect terminals that can corrode, not even screw terminals (QD terminals don't belong anywhere on a boat - maybe on a sound system/speakers is ok.)
When an unnecesary added preheat component fails you're not just screwed, you're really screwed.

1) Will a preheat relay work?  Yes.
2) Wil it work absolutely, positively, 100% of the time?  No!!
3) Is it necessary to have?  No!!
4) Will our engines start very well without it?  Yes, they were designed to!
5) So will it be detrimental to install it, to the point my engine won't start?   Only if the unnecessary relay or solenoid fails (see #2.)
5) Did Kubota have any concern about over-voltage on glow plugs?  Yes, it installed a power resistor to reduce the voltage from 12v.
6) So why then do folks install it?  Beats me, being ignorant of the facts maybe?  Koolaid maybe?  The sheep factor maybe "My dockmate did it"?

If ONE MUST -- install a mounted soecket type with a quick plug-in relay, and keep a spare relay where you know where it is and can grab it within 20-25 seconds.  Or better yet, in 10-15 seconds.