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Ohming out Trigger for merc 650

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Bruce Honnigford

New member
I have a '71 Merc 650 outboard ser #3155373. This is a 4 cylinder unit.

My research has pointed my starting problem to a bad trigger. This may have been caused by removing the battery from a running engine resulting in the engine firing only when the starter is engaged. I am overhauling the engine and have it partially disassembled at the moment.

While shopping for a replacement trigger for 332-4177A3, I purchased a similar old new stock 393-2918a6 which is the wrong part due to bad catalog data.

Recently I found an old/new stock ignition replacement kit 393-3736A78 that includes a newer version 393-3736A79 trigger which should be the correct part for the 650.

So I have 3 triggers: One suspected bad and 2 suspected good.

Before installing the "good"one, I would like to verify if the unit ohms out correctly and compare it to the other 2 for reference.

All the triggers have 3 wires - BLK, BRN and WHT.

I have no schematic of the internal circuit and no specification on the resistance values for the wiring.

If anyone can supply this information I would certainly appreciate it.
 
Thanks, but this is the same information that I read last year that suggested I have a bad trigger. it doesn't give any Ohm readings or schematics.

When I bought my '71 650, it came with a merc 75-78 service manual. Much of the manual is useful.

I was paging through it tonight and found a table in the back of the manual that listed exactly what I was looking for.

Ohm readings for a 393-3736A_ trigger. It says black lead to housing = cont. This tells me I probably bought a good unit.

Tried posting a pic of the page but there is an error uploading it.
 
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