Mercury Ignition Wiring

Fester

Seaman
Joined
Mar 25, 2008
Messages
63
I am atttempting to rewire a new ignition for a Mercury 115 w/ tilt / trim. The replacement ignition that I received has 6 posts

A M M I B C

But the SELOC book states that it is supposed to plug into A M M S B C

I have an "I" instead of the "S" is this interchangeable?

Also, There are 2 "M"s.....how do I know which one takes the black and which takes the Black / Yellow? or does it matter?

Would reversing them cause all of the guages to not work? If not then they are shot.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: Mercury Ignition Wiring

Put an ohmmeter on the ign switch. It is likely the two MM poles are connected in the off position. If so, one gets ground and the other Ign Kill (black/yellow)for an ADI Ignition (non-dissy)

Turn the ign switch to the on position. See if the b pole is connected to the A pole. If so, A is +12VDC for gauges. If you have a dissy in that Merc, the A pole gets connected to the white wire that runs to the switchbox as well. S is likely starter solenoid. Check to see if S gets power only when the switch is in the start position.
If you just guess, or rely on a multi-engine manual (Seloc) you can easily burn something out.
 

DRA2256

Cadet
Joined
May 11, 2012
Messages
7
Re: Mercury Ignition Wiring

I am having a similar problem with my year 2000 mercury 150 XL SW. I recently replaced the ignition switch and now everything seems to work right except that the engine will turn over but will not start. Everything was working ok until I changed the switch to a Sierra MP39090 switch. It has the following poles designated: I M S C B M. I took care to map out all of the wire colors going to the old switch which had the poles designated I S (M A) B M C. The (M C) pole had both letters near one pole. I don't know what brand it is. There was no model number or name on it. Do you think I could have switched the two MM poles?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: Mercury Ignition Wiring

Why are there two I poles? Normally the correct ign switch would have (B)attery, (I)gnition, (M)agneto, (M)agneto, (C)hoke, (S)tarter.

Ignition is usually accessory +12VDC. One of the M poles is grounded. The other M pole is connected to the black/yellow wire.

Sounds like you need to test the functions of each pole when in the off, on and start positions.
 

DRA2256

Cadet
Joined
May 11, 2012
Messages
7
Re: Mercury Ignition Wiring

There is only one I pole. That second "I" is the first word of the next sentence. By the way, I swapped the two "M" wires today and it made no difference. Can you tell me how to get a continuity check to ground on the wire (Black) I suspect is the ground wire?

I'm not sure how to test those pole functions but I have decided to put the old switch back in and see if it works - it did before - I just thought I'd put a new switch in because the old one was getting pretty ragged. Thanks for the swift answer.
 

carholme

Rear Admiral
Joined
Sep 4, 2010
Messages
4,845
Re: Mercury Ignition Wiring

If you look at the M poles, you will see that one is raised higher than the other. The higher one is the kill wire (Black with yellow stripe)and the lower is battery negative (black).

Gerry
 

DRA2256

Cadet
Joined
May 11, 2012
Messages
7
Re: Mercury Ignition Wiring

Great. Thanks for that info. At least now I'll be able to put those two wires in the right place. I appreciate the help. -Don
 

DRA2256

Cadet
Joined
May 11, 2012
Messages
7
Well I fix my problem by taken the new switch out and putting the old one back in. Thank goodness West Marine gave a refund - it was the wrong switch for my boat anyway. Thanks all for the help.
 

Fun Times

Moderator
Staff member
Joined
May 16, 2009
Messages
8,776
Well I fix my problem by taken the new switch out and putting the old one back in. Thank goodness West Marine gave a refund - it was the wrong switch for my boat anyway. Thanks all for the help.
Good to see that you were able to get your engine running once again.:) If you happen to find yourself needing additional questions in the future, Please consider starting a new thread of your own vs tagging onto the end of an old thread like done in here. Please see iboats announcement near the top of the forum page titled: "Help Tip" for their reasoning's....Thank you and happy safe boating to you.:)
iboats Mod team
 
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