1975 Mercury 150 serial 4303395 no spark

[Austinpowers]

I have a 1975 Mercury 150 outboard that have no spark. Serial number is 4303395. I have done some serious troubleshooting already but have not made very much progress. I do know that the rectifier is bad from doing an OHM reading. I’m suspecting that the trigger is bad as well. The motor cranks over fine but O spark. I’ve tested the Mercury switch and have good reading out of it. Tested stator and OHM fine. I’ve put a month trying to do what I can but I’m getting overwhelmed and frustrated. HELP!!!!!!!!

 

[Chris1956]

That motor will have a battery-driven CDI ignition, using a single coil and a distributor. Make sure the engine harness is in good shape.

OK, disconnect the mercury switch, to remove that from the equation. The rectifier only charges the battery on that model, so it is irrelevant.

When the ign key is in the on position, you must have +12 voltage on the white terminal of the switchbox. The red terminal on the switchbox must have +12V all the time. Check those with a voltmeter. Without voltage on those two terminals, you will not have any spark.

The CDIelectronics webpage will have a test for the wiring, switchbox and coil. It bypasses and simulates the trigger to help prove the switchbox and coil are good. You should run it.

Usually the triggers break first and usually the coil is good. Unfortunately the triggers are pricey, so it is best to troubleshoot.

 

[Austinpowers]

Perfect, I have voltage on both red and white terminals. Mercury switch disconnected. Still no spark

 

[Faztbullet]

Trigger bad... #1 killer of triggers are disconnecting battery while running,

 

[Austinpowers]

I have removed flywheel and stator and nut on shaft but having issues removing trigger/housing.

 

[Chris1956]

Gee, on a 1975 Merc 1500, trigger is inside distributor. You will need a service manual to replace it

 

[Austinpowers]

[No message]

 

[jimmbo]

That diagram is for an ADI(Alternator Driven Ignition). Those weren’t used until 1979 or 1980. As mentioned earlier, an inline 150 will have a Distributor battery CD system. If you have an ADI system, there are some unanswered questions