2005 4.3 liter Mercruiser ignition trouble

[kepruno]

For the ground I’ve been using the black wire the goes to the cigarette lighter up by the dash and in the engine compartment the black lead stays clamped right on the battery post. Not sure how else I could be doing it wrong. Can see copper on wires by the cannon plug so I know I was making good contact there.

 

[nola mike]

I’m sure. Had meter in the middle of the connection on the jumper wire, 12v down to 9 while cranking. A splice in the purple wire you mean correct? That’s really all I’ve been checking this afternoon.

IF you spliced into the tach, and if you're getting 9v there while cranking (you should), and if you're getting 4v at the boat side of the plug, then the only things that could cause your drop are a frayed wire doing something funny or a poor splice/connection under the helm in the purple wire (or still a ground). You need to trace the purple from the tach where you're getting 9v until it leaves the helm. I'd also use the same ground point under the helm for all of the measurements.