Slave solenoid clicks once and the starter does nothing

[dhsingleton]

My Merc 5.0 MPI won't start. Battery is good, as I just replaced it and getting 12 volts to the slave solenoid, get 8 volts coming out of slave on the red/yellow wire when I turn the ignition. I put on a new solenoid and it did the same - one click when I turn the key. I have 12V at the starter on the main post, and no stray voltage on the secondary post. I'm still thinking its the starter. Can I jump the starter somehow straight from the battery? I'm concerned too It might be the breaker mounted adjacent to slave solenoid. And furthermore if I can determine the starter is bad, how in the world can I replace it myself? Its buried lower rear starboard!

 

[Bt Doctur]

take a jumper wire from the + battery and touch the large yellow/red at the top of the slave.
starter should operate, if not, battery cable connections are bad, starter/starter solenoid is bad.
In some situations the exaust manifold needs to be removed first. In other cases the engine needs to be removed first

 

[JVM225]

First I would make sure all my battery connections were clean and solid.
The connections on those solenoids go bad too. Try spraying the connections with WD40 and then cranking. The WD40 will provide a temporary connection(until it dries). If it cranks, then you know it's just the connections. Take them apart, clean them up, and you're back in busuiness.
If it doesn't crank, then try replacing the solenoid. They are cheap.
Depending on how the starter sits next to a stringer, they can be a real PIA to change. Sometimes taking the exhaust manifold off on that side makes getting to the starter a little easier.

 

[Steve Craig]

Red/yellow may be to your neutral safety switch at the throttle. I would look there for a bad/loose/corroded connection. Switch closed correctly I'm thinking it should allow 12V through it. Bad connection will mean high resistance & excessive voltage drop.

 

[Mike Blake]

Test the battery. Because it is new doesn't make it good. Is the shifter in neutral? Ask me how I know all of this? LOL