Ok Merc issues

[spareparts]

find the alarm under the dash, it should have a purple wire(key on power) hooked to one side, make sure it has 12 v when you turn the key on, then it should have a tan/blue wire hooked to the other lead, when grounded out, this wire comepletes the circut, sounding the alarm. You can make one using any kind of 12 volt, l,ow amperage, horn or buzzer, seen people use seat belt buzzers before, just make sure its loud enough for you to hear it while underway, and always check the circut by grounding out the wire back at the sensor, with the key on, to check the alarm. If you feel real adventurious, you can hook a red light to the alarm as well and mount it in the dash to give you a visual warning as well, just wire it in parallel with the alarm