My starboard engine has acted weird for a while, sometimes it will not fire until I let go of the key. I knew it was weird but for the most part it started okay.

Now I have changed out the starter for a new mini starter and I hear the solenoid click but it will not turn the motor over. I checked the yellow/red wire from the key and only get 5 volts. I checked back to the slave solenoid and get five volts. Right at the key switch I get eight volts on the yellow/red wire. The port motor gets 10 volts on the yellow/red wire and it turns over the motor without issue.

When I run 12 volts directly to the starter solenoid the starter cranks right over so I know the starter and solenoid are fine.

So, do I have a bad key switch, or a bad connection on the yellow/red wire. I an guessing I should be seeing 12 volts at the key, not 8 volts.

Can I just run a wire from the key switch back to the slave solenoid, or does it have to run through a neutral safety switch?

Thanks

Do you have 12 volts at the + terminal of the key switch? If you do then if you jumper + to the start terminal does the engine turn over? If it does than the switch is bad. If it doesn't then it could be the wiring, neutral start switch or the slave solenoid. If you jumper the two large terminals on the slave solenoid does the engine turn over. If not did you check to see if you have 12 volts on the one side.
What I would do is work my way forward from the slave solenoid if jumping it turns the engine over and jumping the key doesn't.

Thanks, I found the wiring diagram last night so I will trace it back through the neutral switch to the slave solenoid. I will also check the 12v supply at the switch tonight and let you know.

I am guessing the 5 volts was enough to pull in the solenoid on the old starter but not the new one. Hopefully I can solve the issue with the engine firing only when I release the key at certain times also

This a low voltage issue also. Been there, done that, on a few boats.

I do have 12 volts at the red wire on the key.

The neutral switches have yellow/red wires connected but appear to do nothing. I can move the shifter until the switch pops up and the port motor will still crank and the stbd motor still clicks at the solenoid. Going to try a direct wire from the key to the slave solenoid and see if 8 volts is enough to engage the starter solenoid and crank the motor.

Probably go pick up two new key switches tomorrow.

Yeah so running direct from the key switch to the slave solenoid with the 8 volts is enough to pull in the starter and crank the engine.

There is resistance of four volts somewhere between the key and the slave solenoid. What has me confused is why the neutral switches do nothing. There is a yellow red wire to each neutral switch, then back to the harness.

There is another yellow/red wire, purple wire, and red wire that are cut off under the dash with a tag the says "MID" whatever that means. They have number tags, but my Formula wiring diagram only has colors and kinda sucks.

Looks like I need to rewire from the keys to the neutral switches then to the slave solenoids.

Do a search, I have put multiple mercruiser wiring harnesses up on this site.

the neutral switches were bypassed, either because of a fault, or prev owner wanted to start in gear. some engines idles are too high to get out of gear easily and are hard on the drive when shifted into gear.