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Followup To
Question -
1994-1996 approx., My used mower has no spark.It has a 18hp B&S eng. 46" cut. I'm looking for an electrical diagram to determine if I have a problem with an ignition switch or ignition part. I have checked inline fuse, seat kill switch, etc. This mower was bought used and the mower model tag is missing so I am guessing on the year.
Answer -
Most likely the problem is one of the safety switches. We rarely find bad switches unless they're actually physically broke, like the mounting posts are broke off. Usually there is a bad wire where the insulation is rubbed through or the connection is dirty.
Unfortunately most manufactures do not provide detailed wiring diagrams. However there are only a few switches, usually the seat, clutch/transmission and deck. We just follow the wires to the switches, unplug the connector and check the switch with an ohm meter. Most switches are 2 pole switches and are open/closed just like a common house light switch.
To rule out the coil you can remove the blower housing/engine shroud cover and dis-connect the small black wire connected to the coil. With the wire dis-connected you can remove the spark plugs and crank the engine to check for spark.
Do you have a Vangard V twin or a standard L head Briggs engine?
Let me know.
Eric response to Eric Yes Eric it is a twin cyl. and I checked the black wire for short to ground. It was disconnected, and the coil side was shorted to ground. Is it suppose to be?
AnswerIf you are talking about the small black wire on the coil it should not be shorted to ground unless the key is in the off position. When you turn the key off the key switch shorts the coil wire to ground which grounds the primary side of the coil thus shorting the spark to ground and stopping the engine.
Most likely there is a safety switch shorting the wire to ground. I wish there was a fast, easy one step method to finding our where the short is but unfortunately you just have to track it down.
Sometimes you can disconnect each safety switch until the short disappears but sometimes this doesn't work.
In the worst case sceniero you will have to start at the small coil wire and work backwards through the key switch then follow the wire harness to each safety switch.
Another trick that I've used to to disconnect the safety switches and jump the harness pins with a paper clip.
Since you found the coil wire shorted I'm assuming you have a meter of some sort. The 2 pin safety switches are very easy to check; they should be shorted in one position and open in the other position. The 4 pin switches can be more challenging but you normally only find these on the clutch/transmission lever.
Once in a while some manufactures use a safety switch that screws into the tranmsission for the neutral safety switch. Sometimes transmission grease will get in the switch preventing it from working.
You can also check the key switch pretty easily. Usually the ground on the switch is marked with a G and the ignition is marked M or I. In the on position the switch pins should be open and in the off position they should be closed.
How many safety switches did you find?
Let me know.
Eric
