2005 9.9 hp model ELH lanyard stop/kill switch doesn't stop engine

[Mainelyfishing]

My engine runs fine but also keeps running no matter what position the switch is in. I'm trying to narrow down the cause of the problem before trying to replace it or the connectors or get a mechanic. The red button on the end of the tiller will stop the engine but that won't do me much good if I've fallen overboard.

From what I've read online, it seems the kill switch works by grounding out the ignition but I haven't seen specific enough information to understand how to test the switch with a meter.

Is the lanyard kill switch open or closed when in the "run" position? I'm guessing it closes to connect to ground and stop the engine since I've read elsewhere that you can fix nonstarting motors by disconnecting the black and yellow wire. Is that correct?

 

[Mainelyfishing]

Switch works fine (closed in "kill" position, open in "run" position) and all the easily accessible connections test out fine but no ground at the black ground wire despite the tiller red kill button working fine. I'm assuming that doesn't share this circuit and I just need to replace the black ground wire or find its bad connection to the block.