Locking 5hp Mercury trim down

[Terry in Ottawa]

I have a new to me Mercury 5hp 2006 ME5M 4ST serial number 0A107680, on a 12' jon boat.

I can lock the motor in full up trim, and in half-trim, but when the motor is down, as in normal operation, I can't seem to lock it in position.

I worry about the motor rising up when motoring along at full throttle and having the engine come into the boat.

I can see a bracket with two hooks that look like they should hook onto the trim pin, but my hooks don't engage, and if they did I can't see how I'd release them.

What am I missing here?

Here's picture of the motor and a picture from the owners manual of the problem area.

 

[Terry in Ottawa]

Maybe I can add a little more clarity to my request.

I found a diagram of the hooks I'm talking about on a MarineEngine parts list. It's shown under the heading of Clamp Brackets and is listed as #34 16213 3 ARM, Reverse Lock. It sure looks like this thing is supposed to hook on to the pin, #17, that determines the trim angle. I just can't figure out how it works.

The picture below has the part in question circled in red.

 

[Terry in Ottawa]

I think I've figured this out to my satisfaction.

The engine is locked in trim down only when in reverse. My confusion came from my Johnson 25 hp (J25TEEDA) which can be locked down in forward, reverse or neutral.

The Mercury has a pin (rod) coming vertically out of the gear housing directly under the ARM, Reverse Lock. This pin is in a raised position when the gear selector is in Forward or Neutral. When the gear selector is put in Reverse, the pin lowers allowing the hooks on the ARM, Reverse Lock to engage with the trim pin.

You probably have to see it to understand it.