YazFan wrote in message
s.com...
I have a bowrider with a 300HP Merc and Bravo-1. After bringing the
boat home from dry winter storage, my trim sender seems to be faulty.
When raising the drive, the needle on the dash goes from full-in to
full-out in one qick movement as the drive is raising slowly. I'm
assuming some problem with the sender on the lower unit.

How easy is this to repair? It is a 2002 boat/engine. It may be
under warranty, but if it's easy I'd rather do it in the driveway on
the trailer than haul it to the dealer.


I know what you mean about trying to get it DONE by doing it yourself at
home rather than going to the hassle of taking it to the dealer where it
might sit in line for an indefinite period of time (during which, you can't
use it or tinker with it). Am I bitter? Has this caused me to do a lot
more DIY on my boat than any other item or equipment in my household? YES!

First, the Teleflex web site is an excellent resource for basic gauge
troubleshooting. http://www.tflx.com/tech.html.

Specifically, this FAQ will get you going: http://www.tflx.com/faq.html.
It has a section on troubleshooting trim gauges and senders and info on
Mercruiser specs.

The short answer is to simply test the variable resistence of your sender
with a multi meter - to see if it changes smoothly from up to down. The
gauge can be checked by disconnecting it from power (should indicate full
up) and then shorting it to ground (should indicate full down).

If this doesn't make sense to you, the long answer follows. It really isn't
too tough and a definite DIY imho.

I'm no boat electrical expert, but I've messed with trim senders and gauges
a little, installed a sender and gauge last year and had a defective sender,
so I therefore had to learn to troubleshoot it.

As you probably know, it's either the gauge or the sender. Or the ground.
Frankly, I can't remember if trim gauges have a ground, but if yours does, t
hat would be the first thing to check. (My boat's at the SHOP, sitting for
the past two weeks, so I can't go out to check it!!)

My guess, like you, is that it's the sender because the gauge is actually
moving from minimum to maximum, but just not smoothly. This to me indicates
the sender is acting as an on-off switch rather than a smooth variable
resistence switch as it should.

The sender is a simple variable resistence thing, like a dimmer switch on a
light. Resistence should vary smoothly depending on the position. The
range depends on the make/model of the engine (that is, OMC units are
different than Merc units, etc). Some have high resistence at up and low at
down. Others are vice versa. The gauge simply reads that resistence and
has to be matched to the resistence characteristic of the sender. To test
the sender, you'll need to know the spec for your sender - what the
resistence should read at full down vs. full up.

Actually, you don't really need to know the spec - it's probably good enough
just to observe how the resistence changes as you move the sender. It
should be smooth.

But, if you want to be more exact, get that spec. If you don't have it in
your owner's manual, the above faq gives it for most makes and models of
outboards and out drives. It says Mercruiser is 10 ohm Down, 167 ohm Up and
I believe this is accurate - but you can call the dealer's parts guy to
check.

Then you need to tap into wires leading out of the sender with your multi
meter (probably at the far end, by disconnecting them from the gauge) and
read the resistence at full up vs. full down. If there's only one wire
leading from the sender (again, I CAN'T look at mine to see how the wiring
is done, and it's been too long for me to remember!) one multimeter lead
would go to ground.

You should see a smooth transition on the multimeter for the resistence as
the sender moves. Unless you can actually move the sender from it's (not
the motor's) full up to full down, you might not see the maximum and minimum
specs on the meter. But you should be able to get the idea if it's a smooth
change from up to down, not jumping from high or infinite resistence to
minimal or no resistence for example. If you actually take the sender off
and move it manually for it's full range of motion, you should see something
close (maybe not exactly) to the stated specs.

If the multimeter reading jumps, like you're describing for the gauge, the
sender is probably defective. I don't know what you'd further check if
anything, or how to cure this sort of sender problem. As far as I know,
you'd have to buy a new sender and install it. You'll have to get a
mercruiser replacement part, as far as I know there aren't generic trim
senders. The cost is minor (in boating terms!) and the installation is a
reasonable DIY - "if I can do it, anyone can," sort of deal. Seriously,
it's probably easy.

If the sender's good according to the multi meter, then it's probably a
gauge problem (with the grounding caveat stated above). Again, to test the
gauge, you need to know the ohms/resistence spec for your sender/gauge
system. The following assumes HIGH resistence in the UP position (as I have
assumed for Mercruiser). The gauge readings would be opposite if the
sender/gauge is high resistence in the down position.

To test the gauge, turn the ignition on. Remove the sender wire from back
of gauge. By disconnecting, you've made infinite/total resistence, more than
the sender would give in the full up position. Therefore, pointer must go
beyond UP. Next, connect the gauge sender terminal to ground. You've now
effectively given it zero resistence, less than what the sender would read
in the down position. The pointer must go below DOWN. If the pointer moves
beyond both UP and DOWN the gauge is functional.

I hope this helps and makes sense. If you haven't already, it's a good
chance to spend $40 on a cheap digital multimeter and get to know it. Of if
you really want to have fun spending money, you could spend 3X that much and
get a really nice one! It's a handy boat tool and not hard to learn to use.
I bought two cheap ones - one for the shop and one in the permanent box on
the boat. They work fine and totally outshine the old needle gauge
multimeter. So much easier to use for us hackers.

Have fun.

Cam