1972 Merc M650 Ignition Coil Help

[pjc]

Would someone know what resistance values I should expect when measuring the primary and secondary windings in this coil?<br /><br />For primary, I am probing at "+" terminal and ground terminal. <br />For secondary I am probing at same ground terminal and socket for 8mm coil wire to distributer. <br />Also, what resistance values should I expect whe measuring across the two leads (leads disconnected from rectifier)from the stator?<br /><br />I am using a Fluke 87 III multimeter.<br />Thank You,<br />Pat

 

[rickdb1boat]

Re: 1972 Merc M650 Ignition Coil Help

This may help:<br /><br /> web page

 

[MrWick]

Re: 1972 Merc M650 Ignition Coil Help

Just a heads up,I had a merc mechanic do a resistance measurement on the trigger plate(85 115hp inline 6) of my motor with a digital meter and all the measurements were open.On the advice of another mechanic the same measurements were done with an analog meter and all the measurements were correct.The second mechanic said he has seen the measurements on the electronics on these motors not show correctly using a digital meter.

 

[rodbolt]

Re: 1972 Merc M650 Ignition Coil Help

hello<br /> anytime you test a component that may contain a clipper circuit and get a funny resistance reading with a digital swap the leads. some devices are polarity sensitve when testing due to solid state devices. some devices can be destroyed by analog equipment.always follow the manual as to what test equipment to use and try to match the input impedance and applied voltages. the old merc triggers are a witch to test and harder to change. not only that they are getting rather expensive. mine on my old 1500 was crazy. would run like a bat outta hades 99% of the time. sometimes would run all day and then stall and instantly restart. would only do it now and again. the manual says run all the tests and if it passes replace it with a known good part and retest.<br /> so good luck and keep posting

 

[rickdb1boat]

Re: 1972 Merc M650 Ignition Coil Help

Yeah, definitly use an analog meter when testing resistence on any component.

 

[pjc]

Re: 1972 Merc M650 Ignition Coil Help

Thanks for the feedbeck guys,<br />I have been to that web page Rick, and that is where I found the test procedure for the spark box--real good info. <br />Last night I did a "farmer" test of the coil. What I did was remove coil wire from distributer, jumper to spark plug. (I made an aluminum plate w/ 14 mm threaded holes to mount plugs and a wire from plate to ground to engine)<br />I then, using 12 volt batt., ground to engine, "swipped" the positive lead from batt. across "+" lead from coil. The plug sparked so I assume coil is good. I did have a 20 amp inline fuse on batt. "+" lead that did indeed fuse after several "swipes".<br />Hope this test did not harm coil. At least I know it did make spark.<br />Next step is to attempt repair of switch box per another post here, where Rick posted a link to the procedure. Also, have to dig up an analog meter.<br />Thanks guys,<br />Pat