There are two switches incorporated into the throttle control, a thumb
switch for up/down and a separate switch for trailer. In normal operation up
trim is limited when using the thumb switch, the trailer switch raises the
outdrive the maximum, and the thumb switch down position lowers the drive
all the way.
The wiring diagram I have is a schematic, so it indicates or example, a fuse
in a circuit, but not where in the circuit.
I can't get to the wires behind the ghunwale at the throttle control. I'll
have to see if I have the mounting instructions - some of those papers were
with the boat when I bought it new. There's a hole in the bottom of the
throttle handle, but I couldn't feel a screw with either a flat blade or
phillips screw driver. I didn't have any luck with hex wrenches either, but
I suspect that's what I'll need to remove the assembly. There's a thin
plastic shield between the throttle handle and the mount. Lifting it up with
a knife blade, I could see a mounting nut. I can probably get a socket
wrench in the gunwale to remove the bolt, but I don't want to break that
plastic shield, so I want to remove the throttle first.
The fluid level is OK and there's no corrosion on the pistons.

"Tom Francis - SWSports" wrote in
message ...
On Sun, 2 Nov 2008 12:05:02 -0800, "William Andersen"
wrote:

Where do I start troubleshooting my electric trim system?
Nothing happens when I use the Up trim switch - no sound, no movement. The
trailer (up) switch works correctly. The Down switch lowers the motor, but
not the last couple of inches. I pushed it down with my boat pole to get
it
all the way down.
Once underway, I could use the Trailer switch to trim up and the Down
switch
worked correctly.
The boat sat in dry storage for seven months. It took about a minute to
get
the gas pumped back into the carburetor, but then it started right up and
ran great. This trim problem is the only thing not working.
1998 Bayliner runabout (1950CL) with 3 liter MerCruiser sterndrive.

I assume that you mean that you can't trim the outdrive from the
throttle position, but you can trim the outdrive from the bow trim
switch.

Ok, couple of things to look at. First, and probably the most
obvious, is that the trim switch in the throttle housing is stuck or
inoperative. Check to see if you have power to the switch first, then
make the switch (up or down) and see if you have voltage and current.
If you don't once position contact has been made, but you do have
voltage current before the switch, then it's the switch.

If you have power to the Up or Down side of the throttle switch, it's
time to move to the trim switch relay. I don't know where it's
located on your boat, but on my brother's boat (similar outdrive), the
relay is mounted inside the stern above or around the outdrive stern
cutout. You may have to hunt around for it or ask somebody where it's
located on that boat. Again, check for voltage/current in and out on
the relay wiring. Most relays have the in/out schematic on the cover
of the relay. If you have current up/down, then it's on to the trim
motor. That could be a little more difficult - if it's not working,
there really isn't a way to check the internal wiring - you'd have to
work with the outside wiring. There could be a fusable link somewhere
that might need replacing - it would help you to get a schematic of
the outdrive system to help out.

Other than that, the only thing I can think of is that you have a seal
gone in the trim piston(s), it's low on hydraulic fluid (had that
happen to me once a long time ago) or the trim pistons are corroded
and sticking.

Hope that helps.