Rectifier question

[tlewick1]

Last season, my Mercury 1150 (1974-1976) was running fine. I spent the winter restoring the deck-- this year it won't start. No spark. My instinct tells me I accidentally pulled a wire when working throughout the winter. Checking for continuity, I can't chase the brown wire on the rectifier (looking at the wiring diagram, the wire going to the tachometer-- which my boat has none.) I'd assume that regardless of there never being a tach, there should be continuity to the negative terminal. I'm I right?

 

[Chris1956]

If your motor has a distributor, and that is consistent with the year of the motor you posted, the rectifier has no connection to the ign system. In order to have spark, you must have +12VDC on the red wire on the switchbox, as well as the adjacent white wire on the switchbox.

On those old motors, the wiring harness is usually missing insulation and can have broken wires or connectors. I recommend you start there

BTW with no tachometer, the brown wire is open.

 

[tlewick1]

Thanks for the response. The ground just goes through the frame then? I have +12V at both areas that you mentioned, but I'm not sure what to check to see if it's ground. Just check for continuity between the switch box casing and the negative terminal?

 

[Chris1956]

Yes, I would check for the coil casing and switchbox casing continuity to ground. There should be the main ground wire on the lower cowling support, behind the quick disconnect. Ground straps connect the lower cowl to the block. Make sure those are intact. Make sure the starter and distributor ground wire are intact, as well.