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Is my ignition switch bad?

J

john's merc

New member
Hi, I have a mercruiser 120/140 and am trying to get it to run after a 3 year sleep. I've replaced the coil, distributor cap, points and condenser, recharged the battery. I get a great spark from the coil and when I turn the engine over, it fires up but only as long as the key is in the "start" position. When I allow the key to "relax" to the "run" position, the engine immediately dies. The longer I crank the engine, the higher the revs and I'm clearly getting combustion. I get gas to the carb and as well as the spark plugs. I've followed the mercruiser manual for testing the ignition system and despite the great spark at the coil, all further tests of the primary circuit fail (points test, condenser test..). Any ideas?

Thanks in advance
 
Oh, and when I connect a volt meter between the + coil terminal and ground, I get nice fluctuations while turning the engine over but there is no reading when I have the key in the "on" position.
 
Thanks very much. If I'm correct, this is a purple wire from the + coil terminal to a spade connector on the carb choke assembly. I tried bypassing this with wire and alligator clips connecting directly to these 2 points with no success. Should I get a volt reading from the coil when the key is in the "on" position? I don't, and I also don't get a reading from the starter solinoid terminal where the other + coil (purple-yellow) attaches.

Other info-when the key is in the "on" position, my dash instruments work fine and I also get a reading from the water temp. sending unit.
 
The purple-yellow wire energizes when the starter turns to send 12 volts to the coil. The purple wire gets 12 volts in the run position and the resistor wire drops it to 6-9 volts. Trace the purple wire w/a voltmeter until you find the break. The resistor wire may be ok.
 
This also may be a issue with the key switch,

Turn the key to the run position, look at the back of the ignition switch, there should be a Red wire, purple wire and a yellow w/red wire.

Red = +12 vdc
Purple = key in run positon = 12 vdc to ignition, and guages.
Yellow w/red= crank.

If in the run position and you have 12 vdc on the purple then you need to trace it back thru the MAIN connector on the engine. Maybe a bad connection at the connector,

Also I reccomend using a 12 vdc test light so you can see the intensity of the light.
 
Got it. Thanks. One last thing. Are you saying that the purple wire is NOT the resistor wire? According to the wiring diagram in my manual, that is what this wire is called. It goes from + coil terminal to the outside cover of the carb. There is another, black wire connected to the other side of the carb cover that then enters a wire bundle (the same bundle that carries the purple wire) and goes someplace I have not identified because I haven't cut apart the bundle wrapping. This black wire is not listed in my wiring diagram.
 
The purple wire goes from the ignition switch thru the big connector and splits in the engine wire harness to several locations.

coil, choke, alt.

When the purple wire gets divided up. one of the purple wires that goes to the coil is connected/spliced to a resister wire, It is a toatally different type of wire material (it is like a aluminum type materiel and is very stiff and is about 3 ft long and is bent way into the harness and back towards the coil and wrapped into wire harness under the tape). Ford type ignitions used a ballast resisstor vs a resistor wire.

What to do is get a digital volt meter, set it to ohms ( beep on) and just touch the puple wire on the back of the key switch and to the + side of coil. If continuity is there then the wire is not broken. But it does not mean there is no issue with the wiring............
 
OK, did the continuity test and this confirmed a break somewhere. Thanks for all your help. In the meantime, my most important objective is to get the motor running with some good gas (stored for 3 years) and then fog it for the winter. I hooked a lead directly from the battery to the + coil terminal and the engine started right up. I know this will supply 12V instead of the desired 6-9 but I just need to let it run for 30-60 minutes before putting it to bed for the winter. I'll continue the search for bad wiring but may not be able to track it down till in the spring.
Thanks again to all who've helped.
 
The following two posts contain generic wiring diagrams.
first is of the guage cluster
second is engine diagram. This is from a 470 4 cylinder but should be close enough to help.

The basic ignition (purple) circut is the same.

Hope this helps.
 
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