Alarm (Maxum 2500 SCR 5.7 Merc 2002)

[forbes210]

Hi All,

Recently my alarm stopped working when ignition key is in on position. My first thought was that the actual small speaker died but after inspecting it and testing it came out that its fine and works when connected directly to the battery. Does anybody know where else should I look for faulty parts/connections? Maybe some kind of diagram for the alarm system will be helpful. I guess the alarm speaker got to be connected to some kind of module which collects the data from the sensors etc. Thank you in advance for your help.

[mmwjr]

The alarm is a self contained module.

Did you check that it is getting 12V and ground? Purple wire is the positive.

[forbes210]

I got 2 wires from the alarm which one of them is connected to the ignition key and will provide constant 12v positive whenever the key is on position and the other wire (brown with blue stripe) needs to be responsible for triggering the alarm which I'm assuming is ground. Does this wire comes directly from the sensors and its spliced somewhere down the line with water temp, oil pressure and outdrive lube sensors?

[mmwjr]

Originally Posted by forbes210

I got 2 wires from the alarm which one of them is connected to the ignition key and will provide constant 12v positive whenever the key is on position and the other wire (brown with blue stripe) needs to be responsible for triggering the alarm which I'm assuming is ground. Does this wire comes directly from the sensors and its spliced somewhere down the line with water temp, oil pressure and outdrive lube sensors?

Exactly these sensors are normally open circuits and close if a fault condition exists to complete the path to ground. At start up the OP sensor will be closed until the engine has pressure once running, this is why it sounds at start up.

[forbes210]

Is there 2 oil pressure switches? I found one together with oil pressure sending unit and this one controls fuel pump and it seams be closed when sensing correct oil pressure.

[mmwjr]

Originally Posted by forbes210

Is there 2 oil pressure switches? I found one together with oil pressure sending unit and this one controls fuel pump and it seams be closed when sensing correct oil pressure.

Yes one is as you say for the fuel pump. When starting the fuel pump gets power from the starter and once started an oil pressure exists the switch provides the power.

There is another OP switch for the alarm.

[forbes210]

Mike,

Thank you for helping me to understand this system. Came out it was faulty alarm oil pressure switch which is located on my engine next to the distributor cap. Got it replaced and it works fine now. Thanks again.

[mmwjr]

You're welcome, always glad to help a fellow boater.

Enjoy the rest of the season.