Starting Problem

[NoMechanicHere]

Hi everyone. First post here!

Ok, so I've got a Merc 4.3LX/V6 with a BRAND NEW deep cycle marine battery. Went to start her for the first time this year and when I turned the key all I heard was one click - determined the click was coming from the slave solenoid. Tried bypassing the main starter solenoid and got the starter to spin but it wouldn't engage the flywheel. So then I jumped the slave solenoid by connecting the main posts with a screw driver and it did turn the starter AND engaged the flywheel. Thought It was the slave solenoid so I replaced it yesterday and I'm still getting the single click when I turn the key.

Here's the one kicker.... if I disconnect the safety lanyard and plug it back in I can get it to turn over about 1 out of 20 times. It's probably worth stating that when I do get it started the engine runs great.

Here's what I have done so far:
-Replaced battery and confirmed it is fully charged
-filed all connections to the battery, no corrosion on cables
-replaced slave solenoid and filed connectors down
-Checked fuses
-visually checked for crimps in cables

It's probably unrelated but I can't get my stereo amp to power on either. CD player works, but since amp won't power on I have no audio. Checked all fuses and they are good.

Any suggestion as to why it clicks when I turn the key would be much appreciated.

[goodday]

Ck. Grd.wire connections on back of mtr. Should be below the head ,maybe on both sides of mtr., or one wire broke, safety switchest go bad to, or the plug, for a test you might be able to wire jump switch

[AquasitionBoston]

Did you ever resolve this? I'm having a similar issue and could use some pointers.

Engine shut down while under way, had to deploy emergency anchors front and stern in narrow section of river approaching a bridge..!

Definitely have a short somewhere, found and isolated it, but can't start due to one-click nightmare, as you put it. Can start just fine when jumping the back of the solenoid posts.

In your case, what caused the one click? Any idea what you did to resolve it?

[Bt Doctur]

If jumping at the starters solenoid spins and starts the motor but jumping the 2 larges lugs on the slave does not take a jumper from the + battery and touch the yellow/red of the slave . starter should spin .If Yes, your missing the power on the Red/purple. If not ,your missing the connection on the yellow/red from the slave to the starters solenoid