No spark!!!

[Mike3406]

I just baught a 1975 Mercury 850 85hp outboard motor. I had the motor running in my garage and was flooding my garage with my muffs. Decided to move motor to driveway and continue working on it. After I moved it I lost spark. I removed coil and switch box and bench tested and had great spark. Put back on motor and once again no spark coming out of coil pack. Have power to switch box on both red and white (when key is on) wires. Everything appears to be operating right but can't seem to get power to my coil. Any ideas anybody? Not even 10 mins ago I tried it again and had spark for maybe 3 seconds and then lost it again. Any help would be appreciated.

 

[gm280]

:welcome: aboard Mike3406. Great to have you join us...

Sounds like it is some wiring issues to me. Sounds like you have a wire touching every now and then and shorting out the ignition spark. Look for the wires that go for the kill switch system and see. JMHO!

 

[Chris1956]

There is only power to the coil when the switchbox capaciters discharge into coil and spark is generated. You will not read any voltage before or after that.

That motor should have a mercury switch which kills spark when motor is tilted too high. Trace from switchbox to small condenser-looking thing on front cowling support. Disconnect that thingy and recheck for spark.

 

[Mike3406]

Thank you guys. I will try this when I get back home today and let you guys know if it worked.
Could the actual key ignition switch cause no spark for any reason? I didn't have key for the motor and ended up using my old ignition switch. It's a 5 terminal key switch just like the one that was on it and both came out of a mercontrol unit. The wire colors where identical and in the same posts on each switch. Not sure if maybe the key switch might be bad and that causing issue. Fairly new to the boating world but I am quick to learn and have a decent understanding of things. Just not to hot with electrical. Once again thanks for your input and help.

 

[gm280]

Thank you guys. I will try this when I get back home today and let you guys know if it worked.
Could the actual key ignition switch cause no spark for any reason? I didn't have key for the motor and ended up using my old ignition switch. It's a 5 terminal key switch just like the one that was on it and both came out of a mercontrol unit. The wire colors where identical and in the same posts on each switch. Not sure if maybe the key switch might be bad and that causing issue. Fairly new to the boating world but I am quick to learn and have a decent understanding of things. Just not to hot with electrical. Once again thanks for your input and help.

Little confused here. Are you saying you used another ignition switch without a key? Or did you replace the existing one with another one and used that keyed ignition switch after swapping the wires from the old one to the replacement one? Need some clarification. :noidea:

However, that answer is yes an ignition switch has a lot to do with the engine starting. When the ignition switch is in the off position, it shorts the primary windings of the spark coils together stopping all spark to the plugs. That is how the ignition shuts off the engine. Same with the kill switch.

 

[Chris1956]

GM is correct for most OB motors. That Merc 850 should be a battery powered CDI unit, and must have voltage on the ign (white) wire to have spark.

Whereas the OEM ign switch did ground a killer wire, that wire (orange) was not used on the battery CDI Mercs.

 

[Mike3406]

Little confused here. Are you saying you used another ignition switch without a key? Or did you replace the existing one with another one and used that keyed ignition switch after swapping the wires from the old one to the replacement one? Need some clarification. :noidea:

However, that answer is yes an ignition switch has a lot to do with the engine starting. When the ignition switch is in the off position, it shorts the primary windings of the spark coils together stopping all spark to the plugs. That is how the ignition shuts off the engine. Same with the kill switch.

I replace the ignition switch with one from my other boat.
Ignition switch, push choke, neutral switch and tach plug

 

[gm280]

I replace the ignition switch with one from my other boat.
Ignition switch, push choke, neutral switch and tach plug

So basically you changed to an exact same setup from a donor boat. The big question is, did the donor boat parts work before you changed them over? Trouble shooting is a lot easier when you do things one at a time to see the results. When you change a lot of things, and even with suspect parts, you then have to go back to square one and start testing all over again. The fact that you had this engine running in your garage and then moved it out to the driveway, leads me to believe you have something in the wiring messed up. If you have fuel, and everything wired properly, it should run. I say go back over all the connections again and make sure they are nice clean and shiny metal and tight. JMHO

 

[Mike3406]

Sorry it took me awhile to get back to you guys. Kids have been running me ragged this weekend. lol
So I disconnected the kill switch completely. Still no spark. But while inspecting wires I have found that the coating was brittle and falling off to the touch. Wire under coating is green and corroded. I am in the process of ordering a new internal wire harness. My plan till it arrives is to cut away bad wire and temporarily rewire harness if i can find good wire to connect to just to see if I can get spark. I don't plan on using the motor at all till the new harness is in. I am hoping that this will solve my no spark problem but for some reason I am not holding my breath. lol. Could my switch box bench test out good but still be bad for some strange reason? Or do you think that I will resolve this issue with the new harness.

 

[Mike3406]

And what is the best way to test the harness for shorts or anything after I got it redone with the temp fix. Got an email that my harness is now back ordered and the will ship it 2 day shipping as soon as it gets in.

 

[Chris1956]

Mike, CDIElectronics has an "on-motor" test for the wiring, switchbox and coil. It's intent is to eliminate those as a problem, leaving only the trigger as the likely issue. I would run the test, as those triggers can be intermittent and can also fail at any time.

 

[Mike3406]

Ok so I rewired and retested stuff a bunch of times. Narrowed it down to the distributor. I baught one in eBay for 300 dollars used but refurbished with new cap, rotor. Arrived in the mail today and I put it on right away and boom it fired right up.
Thank you everybody for your help. Now I just have to install net cables and adjust throttle and gear shift cables and should be good to go. May have some questions on how to do that if I can't figure it out. Going to go back out and work on it some more tonight after kids go to bed.