I've got a '85 Mercruiser 3.7l 170.

In the last two trips, I've had trouble out on the water shifting from
forward-neutral-reverse and vice versa. There really isn't a neutral,
which makes docking a challenge, you can imagine.

There's a good bit of resistence at the remote control where I fight it in
and out of gear... the resistence may grow as the engine warms (or I may
just tire).

After the first time, I ran it on muffs in the yard for more than an hour
and the problem seemed to go away, which prompted me to go out the second
time. So maybe there's something to the added pressure on the prop, I
dunno.

I figure the problem is either electrical (shift interrupt switch) or
mechanical (shift cables, levers, etc.). I'm inclined to attempt to debug
the electrical portion before taking it to a mechanic. I read in my
Clymer's manual about the shift interrupt switch and saw a wiring diagram
of it, but for the life of me, I can't find it when I'm looking down on
the engine.

Does anyone have a helpful photo or advice?