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Installing engine hour meter
|Author||Topic: Installing engine hour meter|
posted 04-25-2005 09:09 AM ET (US)
I installed an engine hour meter on my 2003 160 Dauntless this weekend, and thought I'd share my experience with anyone who might be interested in the same project on a Dauntless or 170 Montauk, which has a very similar electrical system.
After much debate on where to mount the meter, I decided to install it on the inside of the console. This allowed me to avoid cutting any additional holes in the console that I might come to regret some time in the future. I bent an L-shaped bracket out of aluminum stock, and drilled/cut it to accept the meter. The short side of the L was attached to the inside of the console on the aft edge of the console door, using one of the bolts that secure the console door frame. This places the meter out of the way when putting things in or out of the console.
Strangely, the electrical hookup turned out to be the hard part. The wiring diagram in the owner's manual is somewhat incomplete, and does not show any information for engine-related wiring. From the documentation for wire colors, I determined that the ignition wiring is violet. The ignition switch is a sealed unit with wires sticking out the back; there are no screw terminals on it. What's more, the wiring does not go anywhere particularly accessible- about 2 inches from the switch, there's a shrink-tubing-covered coupler that splits the violet wire, and most of it disappears into the main wiring harness.
After more poking around, I found that a violet wire runs to the tachometer and leads to a screw terminal marked "IGN". This was a very promising sign, and conveniently, the adjacent terminal is labelled "GRD". I routed the hour meter wires (with some ring terminals swaged, soldered, and shrink-tubed on the ends) up to the tach and connected them. I had to remove the tach from the instrument panel to get unobstructed access to the connections.
After reconnecting the battery (I once learned a hard, expensive lesson about doing electrical work with the battery attached), I was ready to give it a try. I turned the key, and ... nothing. Silence. Dead motor. All the other electrical items still worked. Oh sh**.
After searching for any circuit breakers related to the engine (there aren't any), I pulled off the engine cowl and quickly found a set of fuses on the front starboard side of the Mercury 115 4-stroke. A 20-amp fuse was blown. I replaced the fuse, disconnected the hour meter (at the back of the meter where it was much more accessible) and tried again. The engine started perfectly. Whew!
I rang the wiring for any short circuits (none), reconnected the hour meter, and tried again. Another silent engine and blown fuse. I'm still very confused about how I generated a short circuit, since the hour meter shows about 4.5 megohms across the terminals.
Good sense probably would have had me just quit at this point, but I remembered that the boat is wired so that the instrument lights are on whenever the ignition is on. I moved the hour meter positive lead from the IGN terminal to the LT terminal on the tachometer and reconnected the battery again. Cringing, I turned the key... and the motor started and ran perfectly, while the hour meter ticked away the 1/10s.
I still don't understand why connecting to the IGN terminal caused a problem, but if you're wiring an hour meter into a Dauntless or a Montauk, take the benefit of my experience and don't do it like that! Instead, connect to the instrument panel lighting circuit.
posted 04-25-2005 02:37 PM ET (US)
I have a lot of experience wiring up instruments on Mercury engines, and have never encountered your problem. You were right not to cut into the ignition switch, as the engine electrical harness has the purple (ignition), black (ground) and various senders leads in it already. An hour meter DOES connect to the IGN and GRD terminal of ANY gauge, which on Mercury are purple and black. I have no idea why you were shorting out the 20 amp starting circuit.
Since Mercury tends to wire the instrument lights to always be on with the ignition, connecting to a lamp terminal is the same as connecting to the IGN terminal.
Hour meters and volt meters are the two easiest gauges one can install and connect.
posted 05-19-2005 08:30 PM ET (US)
Mercury make an engine monitor that mounts under the cowl of the OB. Connection is simple the wire from the monitor is just wound around a plug wire. It only works from pulses from the plug wire when the engine is running, no false readings from the ignition switch being left on with the engine not running.
It's worth checking out.
posted 05-21-2005 09:24 PM ET (US)
Dick- Do you know what this part number is and if it would be applicable to ob's other than a Merc
posted 05-21-2005 11:24 PM ET (US)
I also did not mount my hour meter on the dash. I elected to purchase a plastic project box from radio shack and put the hour meter in there. Hook up the electrical and your done.
Once you open up the access door, you can see my little plastic box and the hour meter.
posted 08-03-2007 08:44 AM ET (US)
The link to the Sendec hour meters I provided above has meters that use a wire wrapped around one of the spark plug wires as the sensor. Another advantage is that it will only record hours when the motor is running, not when the power is on without the motor running. They are self powered via an internal battery so no additional connections are necessary. Couldn't be simpler to install.
Sea Antsy --
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