Glow plug switch question

[Tallship2]

So the MX25 wont fire up after much cranking. I checked the fuel filter and the fuel pump and both appear to be working. I thought I'd check the glow plug switch for power, and I am getting twelve volts across the two back ends even when the button is not pushed in. Is this right? It would seem that I should only get voltage across the terminals when the button is pushed in. Am I missing something?

[mark_53]

I am getting twelve volts across the two back ends even when the button is not pushed in. Is this right?

Two black wires would usually be 2 ground wires, but who knows what a PO would have done.  Check the terminals on the switch or the switch itself then determine which terminal the wires are supposed to be connected to.

[KWKloeber]

First, are you referring to an M-25XP engine?

Second, What do "back ends" mean?  The preheat switch is a push button, no?  With brass screw terminals on it?

The easiest way to check plugs is put a voltmeter between the tip of a glow plug (the wire terminal) and engine ground. You should get nominal 12v with the switch ON.  With the plugs energized you should be able to touch the plug but not hold onto it too long.  If they're lukewarm it's either a voltage issue or they're toast (replace them.)

One side of the switch should be 12v TO PANEL GROUND. The other side should be 0v TO PANEL GROUND.

You might have a vacuum leak and have air in the lines/injector pump.  Is the fuel stream clear, no air, foam? What changes or servicing has been done recently?

Is the injector pump receiving fuel?

[Jon W]

If not your glow plug system; FWIW - a while back I couldn't get my M25XP to start. It ran fine the day before. Turns out that the engine shutdown cable didn't push the lever on the engine back to the engine running position, even though the handle at the engine control panel was pushed completely down. Something to add to your troubleshooting list.

[Tallship2]

Thanks for the replies. Yes, it is an M25XP, typo on my part. I just realized that I was testing the glow plug button the wrong way  Thanks for the advice on the shutdown cable, I'll check that out.

[Ron Hill]

Tall : if you are having trouble with the "old panel" glow plug push button, buy a new key switch that has the three position and rewire!!

A thought

[Tallship2]

Ron- thanks for reminding me- I had bought a new switch after the old one died, and I think it is a three-position. If it's the old switch, problem solved!

[Tallship2]

Hi guys- yes it was the glow plug switch. I do have the three-way ignition switch so I will send the wire to the third pole on the switch. Question is, does anyone know what the gauge wire is? It looks like 12 to me, but it may be 14.

[KWKloeber]

Do you have the preheat solenoid/relay installed in the engine compartment?  If so the circuit can be 14 gauge to there.
If not the circuit should be 10 ga all the way to plug #3.

The original preheat circuit in the OEM harness was 10 gauge.

[Tallship2]

Not sure, but all I am doing is taking the original wire from the glow plug button that goes to the engine and splicing it to the new ignition switch.

[KWKloeber]

The original harnesses on the M-25s and XPs all had 10 gauge for the preheat.

All due respect to Ron but there's an issue doing the switch switch you're planning.
The push button preheat switch is heavy duty and the contacts are meant to carry that high load (if you don't have the preheat solenoid/relay.)

The ignition switch contacts are not rated for the high amperage and can get burned - and then you have a failed switch. Of course it's an even greater concern for those w/ 4 cylinders.

I suggest you investigate how your preheat works before making a change (it's a GOOD idea anyway that we all know about every system on our boats and how they work.

But YBYC whichever way you go.

[Tallship2]

KW- I did some checking and here's what I found. The replacement switch that Catalina Direct sells is rated at 10 amps. I then looked up the ignition switch that I previously bought and it is rated at 15 amps, so it would seem that the three-way is actually more robust than the original switch. Or am I missing something?

[KWKloeber]

The replacement switch that Catalina Direct sells is rated at 10 amps. I then looked up the ignition switch that I previously bought and it is rated at 15 amps, so it would seem that the three-way is actually more robust than the original switch. Or am I missing something?

Tall -

YES!
Missed that CD is not "always" ... the best source for, containing the best information about, and/or exhibiting that it thas sufficient knowledge about some systems on our boats (I have a slightly lower rating than most here, more like "CD = buyer beware.") 
STILL --- don't get me wrong because CD does have some good stuff, but they disappoint as to what the source/resource should/could be (especially seeing that it has an ex-CTY person who can guide them.)

The preheat switch you want is a quality Cole Hersee M-626 BP (rated 35 a.)
16 boat bucks for a quality switch at Defender vs 34 bucks at CD for a garbage one.

There's an example of CD doing CTY owners dirty.  If CD wants to sell that switch, then they should offer the heavy-duty one and caution about when their cheap-a$$ switch (cheap quality not cost) is suitable -- like for "A" and "B" series engines or for when the owner has installed the preheat solenoid.  I don't believe that CD has the knowledgebase to know that type of stuff.  Maybe, but I don't believe it.  Ok, enough dumping on CD.

Preheat and switches 101 -

The plugs are 6a each per our parts, etc. manuals.  Not so, they are closer to 8 - 10a each (new ones for some reason draw more than the rating on older ones, tho I haven't checked the actual draw myself from the OEM plugs.)  Another owner checked and said his new set of 3 drew 27 amps.  Anyway say 30a thru a 15a or 20a switch is not good   It won't blow up, and it's not fatal -- but it can fail prematurely. 

BUT, where did you see the rating for the old (brand?) switch and new CD switch you refer to?  Based on experience I doubt the CD switch is 20a.  I haven't a clue the brand but one needs to be VERY careful about ratings (and website specifications.)  Figures lie and liars figure (not always intentionally, many times it's a lack of knowledge about specific applications.)

MOST ignition switches -- rated 15a or 20a on websites are NOT the rating on the start (or glow plug) contacts (which is typically 5 amp.)  Secondary websites oftentimes have incorrect specs -- when critical I usually go straight to manufacturer datasheets.  The best Cole-Hersee marine ignition switch is rated 5 amp (start.)  Then we're talking 30a thru a 5a switch.  YIKES

IPSO, use a heavy-duty push-button switch for preheating unless there's a preheat relay installed or it's for a Universal "A" or "B" series engine.

-k

[Tallship2]

Thanks KW, for $16 I'll buy a new one from Defender. Interestingly, CD offers only one switch and says it's for start or ignition. Also, how do I find out if I have a pre-heat solenoid, just in case it ever goes bad?

Update- Defender has a $25 minimum and wants $20 for shipping Found the switch on Amazon for $18, no shipping

[Stu Jackson]

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Also, how do I find out if I have a pre-heat solenoid, just in case it ever goes bad?

With your hull #, your boat didn't come with one.  Only a PO could have installed one.

The tech wiki shows how to do it. 

Glow Plug Solenoid or Relay Installation for faster starting 
https://www.c34.org/wiki/index.php?title=Faster%2C_More_Efficient_Glow_Plug_Heating_with_a_Solenoid