How to repair a Mercury ignition


Recently picked up a broken 9.8 HP Mercury off of Kijiji, I was originally going to use it for parts but the engine had good compression and the lower unit was in good shape. Only problem though, one cylinder was getting a spark pulse… Here is the ignition removed from the motor … hmm I wonder what could be the problem.

2 green wires on the right are for one coil, the 2 wires beside them are for the second coil.


All the wires were badly rotted but this wires rot went below the potting. The potting on the back of this ignition is silicon potting and was easy to cut with an exacto blade … if this were epoxy potting then I dont think I could of fixed this.


With the potting removed I was able to get back down to copper wire with only a hint of corrosion, i dont have a picture of the repair but its a butt connector, soldier, heat shrink and “Goop” glue. I’ve used goop for quite a few things and it filled in the potting very well. Below is the ignition all fixed up. All the other wires have been heatshrinked to help defend against more wire rot, the wire that is exposed is still in good condition. The white wire is the wire I repaired.


Left motor is the 9.8 HP with the electronic ignition, right motor is a 7.5 HP with a points ignition …. 7.5 is gonna turn into the parts motor 😀


Tested spark and now both coils are firing, tomorrows to-do list is now to pound in some new crank seals and put some gas in the carb… see if we can make some smoke 😀


Motor has received almost 100% new wiring now … everything was rotten. Even the kill switch was rotten, all the wire insulation flaked off but on the plus side it had aluminum wiring so all i did was snip most of the old wiring off, soldier new copper wires back on, where the wire entered the switch i couldn’t insulate so i covered the bare wire in liquid gasket and then slid heatshrink right up to the end of the switch … you can see it in the picture. The brown goop is liquid gasket.


BTW a new 3rd party ignition module is about $200 …yeah. Oh and by the way – check out for more DIY auto tips 🙂