What the inside of a bad slave starter solenoid looks like

[isaksp00]

Since I just put in a new slave starter solenoid I decided to see what the bad (intermittent starting, clicking, usually no ignition) one looked like. Here is a photo of the interior after I cut the metal tabs holding it together and pulled the cylinder out, the one that houses the actual magnet part and plunger. You can see one of the two copper contacts through which the starting current flows is pretty black. The magnet driving the plunger seemed to work OK, so I guess arcing did this. I wonder what would cause that - maybe the magnet coil is actually weak and it let the contact disc that touches those two contacts stutter up and down?

 

[kenny nunez]

I also took one apart by straightening the tabs. I also saw the black spots. I repaired mine by pushing out the small studs carefully with the plunger, then the large studs,cleaning them and slightly bending the tabs toward the plunger. Needless to say the wires are really small so I was careful not to break them. Over tightening the 1/4” 20 studs against the body will tend to pull the contacts away from the plunger. I rebent the tabs and it works great.

 

[isaksp00]

This was kind of a learning experiment for me. I was not able to get the magnet out without breaking the thin ignition switch feed wires, so it is toast. But, for about $25 for a Merc branded solenoid, which I hope will last a number of years, it didn't seem worth it to do much to fix the old one, tho if I could have easily done so I'd have had an emergency spare. That in itself is not critical, as in a pinch I can remove the insulator and jump the leads to kick over the starter. I now have a piece of wire in the boat I can use for that purpose.

It would be interesting to know if there is a way to prevent this kind of arcing carbon damage in future.