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Author Topic:   OMC c.1977 Ignition Switch
ACalcutt posted 05-04-2006 07:14 PM ET (US)   Profile for ACalcutt   Send Email to ACalcutt  
I am trying to restore the wiring to a c.1977 OMC ignition switch which I may have wired incorrectly.The connections on the old switch are labeled C S M A M B. I took that off a year ago so I do not know what was connected to it.

The replacement switch is marked S I M C B M . An identifier "A" is marked next to the connection labled S, but it seems like there is no connection for it.

The wire colors I have are, red w/purple stripe, rlack w/yellow stripe, purple, purple w/white stripe, black(2), and white.

I tried making it work from the information at and but it did not work.

Chuck Tribolet posted 05-04-2006 08:39 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
My 1997 90-HP manual talks to a switch labeled like your old
switch. That old switch works like this:

With the switch off, M-M is connected.
With the switch in the run position, B-A is connected.
With the switch in the run position and pushed in, B-A-C are
With the switch in the start position, B-A-S are connected.
With the switch in the start position and pushed in, B-A-S-C
are connected.

A=? (but hot with ignition on)
C=Choke (really prime, but same effect)
M=???? (it goes to the power packs, and I'd guess it's
a kill switch)

Color coding:
B=Red with purple
S=yellow with red
C=purple with white
M=black, and black with yellow

You'll need to ring out our new switch with an ohmmeter,
but I'll bet it behaves just like the above, except that now
instead of A, you have:

Your color codes are a bit different. I'd have a starting
assumption that one of the black wires has a faded white stripe
somewhere, and ignore white wire.

You may have blown a fuse.


ACalcutt posted 05-05-2006 12:50 AM ET (US)     Profile for ACalcutt  Send Email to ACalcutt     
One of the black wires is just ground to the casing. The other black wire comes in with the other wires. I think they go to the same terminal post. The white wire comes from the neutral switch. Where is the fuse located? Is it [under the engine cowling] or somewhere in the wiring [harness]? Also, thank you for your post. It should be enough for me to get [the ignition system] working. Now that I know what the wire are it will be easier to test.
Chuck Tribolet posted 05-05-2006 08:23 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
The fuse will be under the cowling.


jimh posted 05-05-2006 09:10 AM ET (US)     Profile for jimh  Send Email to jimh     
The color code of the wiring used in OMC electrical harnesses is provided in this article in the REFERENCE section:

You should compare your wiring with that described in the reference article. If you find anything that is not correlated, please let us know and we can try to deduce what that wire may be used for.

The description Chuck provided for the operation if the ignition switch makes a good fit with my recollection of my OMC ignition switch. The use of the designator "A" to represent the battery voltage is a common convention in electrical schematics. Thus the A-lead is the positive voltage from the battery via the ignition switch.

Perhaps M was for "man overboard," i.e., the safety kill switch. [Or Magneto, from older ignition sytems.]

jimh posted 05-05-2006 09:44 AM ET (US)     Profile for jimh  Send Email to jimh     
As a general rule when disassembling any electrical wiring, it is a good idea to make a sketch and take notes of the arrangement of the connections as they existed before disassembly. This will be useful when re-assembly is required.
ACalcutt posted 05-05-2006 07:22 PM ET (US)     Profile for ACalcutt  Send Email to ACalcutt     
I ended up with it connected like this

B - RED (battery)
S - WHITE (to neutral switch)
C - PURPLE w/white
M - Black(x2)
M - Black w/yellow

I was not sure what M was which...I tried it both ways (should I try putting the blacks and yellow on one connection)

the switch worked exactly like the above post stated...and I am getting voltage from Red w/purple. I is the equivilent to A on my new switch. when i turn the switch with it connected I get 12v out of I, S, and C correctly

the engline still does nothing when I turn the key

Chuck Tribolet posted 05-05-2006 11:26 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Blacks to one M, black with yellow to the other M. Doesn't
matter which.

I'd check the neutral swtich. It should be conducting with
the shift in Neutral.

The next thing to check is whether your have +12 at the
big wire at the solinoid all the time, and +12 at the little
wire at the solinoid when you turn the ignition to start.


jimh posted 05-06-2006 07:38 AM ET (US)     Profile for jimh  Send Email to jimh     
I believe that the color code information mentioned in the REFERENCE section is correct. I also believe that Chuck's description of how the switch connections operate is correct.
Chuck Tribolet posted 05-06-2006 08:35 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Another thing to check is whether the solinoid is working at
all. Jump 12V from the big wire to the the little wire.
Engine should turn over. If not, dead solinoid or dead


jimh posted 05-08-2006 08:11 AM ET (US)     Profile for jimh  Send Email to jimh     
I had an intermittent failure of the starting circuit on my c.1992 OMC engine. There are many contacts and connections in the starting circuit, including a safety switch in the throttle/shift controls which is designed to prevent starting the engine when the shift is not in neutral.

To cure the intermittent failure of the starting circuit in my c.1992 OMC engine, I carefully cleaned and checked every connection. There is a very unusual splice connection associated with the neutral safety switch which occurs outside the switch and under a rubber insulation cover.

Ultimately I replaced the solenoid. The replacement solenoid is not very expensive, about $24. This has to be one of the least expensive components on any modern outboard motor. The solenoid seemed to be sensitive to heat. If the engine was allowed to heat soak for about 30-minutes, it was often problematic to start due to a solenoid failure.

Since cleaning all of the contact in the starting circuit and replacing the solenoid, I have not had any intermittent starting problems. I believe I have corrected the problem. It was probably a bad solenoid all along. I drilled out the rivets and examined the original solenoid to see if there were indications of arcing of the contacts, but it looked good. Apparently the coil winding must have been flakey, and it reacted to heat sometimes by becoming non-operative.

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