No ground @ coil...safety switch?

So the boat will not fire up today. Quickly figured out there was no spark. Grabbed a multimeter and tested the + and - on the coil, it is 0 while sitting and 12V while cranking, but ONLY if i touch the negative lead of my meter to the metal engine block, it appears that the (-) side does not have a path to ground. My first though was to make a new ground, then i realized it may be a safety feature to kill the engine. There are 2 wires from the (-) on the coil, both disappear into large harnesses/connectors so impossible to trace. Anyone know what would cause loss of ground to the coil?. I naturally think that any kind of kill switch/safety/esa fault would kill the (+) to the coil, but who knows?

its an 86 OMC 2.5

thanks

Re: No ground @ coil...safety switch?

nick_vw said:

it appears that the (-) side does not have a path to ground.

Click to expand...

the ground side is switched twice per revolution by the points in the distributor when the distributor rotates. That's how breaker point ignition works. Good thing you didn't "make a new ground".
See how the points are switching the ground side:


Your real problem, if I'm interpreting your post correctly, is that you don't have V+ to the + terminal of the coil with the key on (was the key on?). If so, trace that back towards the ignition switch. You may have a burnt out resistor wire (purple/red I believe). It works like the ballast resistor in the above animation, but OMC uses a wire instead of a ceramic resistor like pictured.
You should have about 9V+ with key on (the V drop is due to the resistor wire), and 11 or 12V when cranking (the resistor wire is bypassed when cranking for hotter spark to get engine started).

If the points are not recent, it is very possible there is a film of corrosion that is preventing the grounding of the coil required to make a spark. Cleaning the points with a piece of emery cloth may get it started, but change the points annually anyways. It's part of the annual tune up.

Re: No ground @ coil...safety switch?

thanks for that picture, clears it up. Boy i had that backwards:lol: . Ok, it appears that there is +12v on the hot side of the coil with key on. The points are new just before i pulled it out of the water in October, stored until last week. I opened and gave em a quick buff with some emery cloth. The negative terminal on the coil has 3 wires. One goes to the distributor, and two disappear into the thick wiring harnesses. What are the purpose of these wires? one goes through a 2pin plug/connector before disappearing into the main harness. I believe they are brown/blue striped.

Also have some gremlins up front messing with my gauges, might be missing a ground causing the gauges to max out and one of the rocker switch lights to back-feed with ignition on. Its a wiring nightmare behind there!! Can they be related? I remember something about a tacometer wire causing some mercs to not run properly, maybe i'm seeing something similar.

Re: No ground @ coil...safety switch?

the 3 wires on the neg side of the coil go to
1. the ESA module (which can simply be unplugged for troubleshooting), 2. the tach (which if your gauges are acting up could be the culprit- grey wire), and 3rd goes to the points in the distributor.

Re: No ground @ coil...safety switch?

update: fixed the problem. Corrosion had broken a medium sized ground wire on an engine bracket that apparently both feeds the instruments and either the condensor or points, although I can't tell which. Anyway, now she runs.

thanks again for the help. Without it I would have stupidly grounded the coil:facepalm:

Re: No ground @ coil...safety switch?

nick_vw said:

update: fixed the problem. Corrosion had broken a medium sized ground wire on an engine bracket that apparently both feeds the instruments and either the condensor or points, although I can't tell which. Anyway, now she runs.

thanks again for the help. Without it I would have stupidly grounded the coil:facepalm:

Click to expand...

hi, i have the same problem, can you point out which engine bracket it is. thanks.