Newbie questions about Alarm testing etc. 1988 135 Mercury 0B333118

Hi All, I just purchased my first boat, a 17 foot speed boat and it has a 135 Mercury outboard. I have no manuals so Google is my best friend and I turned up here pretty quickly. I have had a good look around the net and have some questions about how I should expect the alarm system to work, and how to test it too.

The Serial Number is 0B333118 which I beleive is a 1988 model, it is a V6 2-stroke with oil injection (seperate oil tank) and I beleive it is 2.0 litres in capacity.
It starts, runs and the gears seem ok Forward and reverse) and so far I have only run it up in a water tank.
As an automotive petrol-head, I wish to make sure it is in good shape before taking it out on the open waters.

So,
1/ after I have inserted the key and when I turn the ignition on, should I hear any alarms or check beeps? (I though I would, just to be sure that the alarm buzzer works)
See here for a pic of my controller, not sure of the model, but it has a kill swith (which works) a choke lever (seems to do nothing) and a "throttle friction" rotary switch.

http://homepage.ntlworld.com/s.taylor8817/Boat/Controller.JPG

2/ How do I check the over temp sensor? (will it only work when the engine is running, or can I check the functionality when the engine is NOT running, which I would prefer)?
I read on the net about a tan wire. Is it the one that comes out of the bottom of the wiring loom multiplug and goes to the the top half of the Left Hand cylinder head? if so, I guess I can check the alarm by disconnecting this wire and grounding it?
When I tried this, nothing happened, actually, I checked the continuity and the wire is constantly grounded through what I am assuming is the temp sensor.

Here are some pics of this wire and where it goes to.

http://homepage.ntlworld.com/s.taylor8817/Boat/TanWire.JPG

http://homepage.ntlworld.com/s.taylor8817/Boat/TempSensor.JPG

Should I remove this sensor, clean it up and check it on a test rig?

The dash on the boat has a temp gauge. I dont know if it works, so I am not sure if this tan wire sensor (if it is one) is the temp gauge sensor or if it is the alarm temp sensore?

3/ How do I check the low oil condition?
I removed the filler lid, to expose the float, and hoped that as the float fell, an alarm would sound, maybe a beep beep beep beep?
Nothing sounded.
I checked the continuity of the float switch, and it works, there is continuity when the float is at the bottom of its travel.

So, are my expectations of how the alarm features should work, correct?
A/ a test alarm when the ignition is turned on,
B/ a constant alarm for over temp condition
and
C/ an on/off alarm for low oil condition.

Many thanks is advance, I did search this site but did not find a comprehansive answer.

Re: Newbie questions about Alarm testing etc.

Your assumptions are pretty well correct.

IF the alarm module (and/or the alarm horn) are working correctly you should get a single, short "beep" on start-up (when you turn the key to the "on" position).

From what you describe it sounds like either your module is shot or the horn is bad (or the wiring in between is bad somewhere).

So first I will try and explain how the system works.

Your temp sensor and oil level sensor are designed to complete the alarm circuit should a (failure) occur at either of their locations. The horn is constantly "powered" and if either sensor detects an issue they go to ground and the horn goes off.

The horn circuit starts with the purple wire (#2 pin) in the harness. This originates at the alarm control module (small black squar'ish box). It goes up to the horn, either in the control (shifter) or the dash and then returns via the tan/blue wire (#3 pin).

The tan/blue wire connects with a small terminal block. A black wire leads from the terminal block to the temp sensor and a tan wire leads back to the alarm module. The terminal block is grounded via a black wire - additionally, a black wire piggy-backs over to the alarm module as well from that little terminal block.

The temp sensor works on simple resistance. As the temperature increases, the resistance weakens. If the temp sensor detects an overheat (above 195 degrees), the resistance drops to near zero (0.1 to 0.2 ohms), that completes the circuit and the alarm goes off - "beeeeeeeeeeeeeeeeeeeeeeeeeeeep".

The oil level sensor works just like a simple switch. When the oil level gets low, the magnetic float in the tank "sticks" to the sensor and completes the circuit. The power from the completed circuit goes to the alarm module which "intermittently" grounds the circuit so that you get a "beep beep beep".

The alarm modules only "real job" is to produce an intermittent beep to differentiate between a temp and oil alarm. However, since they piggy-backed the circuit power through it, if it fails the entire system doesn't work.


The tan wire you note could be the feed for the temp gauge. That wire should be separate from the main harness (and could be bundled with the trim/tilt wires). Follow it back to the engine and see if it ends in a temp sensor (which would be separate from the one in the alarm circuit).

Hopefully I have given you enough explanation to troubleshoot your system. If you have a specific question, don't hesitate to post it up (or if I have confused you more - let me know )

Re: Newbie questions about Alarm testing etc.

galamb said:

Your assumptions are pretty well correct.

IF the alarm module (and/or the alarm horn) are working correctly you should get a single, short "beep" on start-up (when you turn the key to the "on" position).

From what you describe it sounds like either your module is shot or the horn is bad (or the wiring in between is bad somewhere).

So first I will try and explain how the system works.

Your temp sensor and oil level sensor are designed to complete the alarm circuit should a (failure) occur at either of their locations. The horn is constantly "powered" and if either sensor detects an issue they go to ground and the horn goes off.

The horn circuit starts with the purple wire (#2 pin) in the harness. This originates at the alarm control module (small black squar'ish box). It goes up to the horn, either in the control (shifter) or the dash and then returns via the tan/blue wire (#3 pin).

The tan/blue wire connects with a small terminal block. A black wire leads from the terminal block to the temp sensor and a tan wire leads back to the alarm module. The terminal block is grounded via a black wire - additionally, a black wire piggy-backs over to the alarm module as well from that little terminal block.

The temp sensor works on simple resistance. As the temperature increases, the resistance weakens. If the temp sensor detects an overheat (above 195 degrees), the resistance drops to near zero (0.1 to 0.2 ohms), that completes the circuit and the alarm goes off - "beeeeeeeeeeeeeeeeeeeeeeeeeeeep".

The oil level sensor works just like a simple switch. When the oil level gets low, the magnetic float in the tank "sticks" to the sensor and completes the circuit. The power from the completed circuit goes to the alarm module which "intermittently" grounds the circuit so that you get a "beep beep beep".

The alarm modules only "real job" is to produce an intermittent beep to differentiate between a temp and oil alarm. However, since they piggy-backed the circuit power through it, if it fails the entire system doesn't work.


The tan wire you note could be the feed for the temp gauge. That wire should be separate from the main harness (and could be bundled with the trim/tilt wires). Follow it back to the engine and see if it ends in a temp sensor (which would be separate from the one in the alarm circuit).

Hopefully I have given you enough explanation to troubleshoot your system. If you have a specific question, don't hesitate to post it up (or if I have confused you more - let me know )

Click to expand...

Awesome information, I know this is an old thread and it has been a while but I would like to ask a question. I have disconnected the module and I would like to get the alarm horn to beep if the temp sensor senses if it gets hot. Where do I connect the wires to get it to work.

Thank you in advance for all your help.