2400 SCR Intermittent alarms
I have a yr 2000 Merc 5.0 L Alpha , single Carburetor, with enclosed San Juan cooling system.
Eng Serial number 0L692217
The alarm is intermittent and has no pattern, alarms for a few seconds at different speeds etc.
I have eliminated the leg bottle and oil pressure switch, the temp sensor (which is new) is the only thing connected.
The engine is not running hot (checked with other temp gauge and laser temp gun)
I look at the manual wiring diagram and it shows a sensor with only one wire (I am not referring to the temp gauge sender) it shows the sensor grounding through the body of the sensor, however mine has a sensor type 805218t (I see some later models had this) which has 2 wires one yellow and one black, this sensor appears to have the correct ohm readings for the different temperatures when tested.
I see the yellow wire goes to the ECM (pin H) and the black to ground. (ECM PART # 86 1459-1, 5.0L G + ALPHA)
Can anyone please tell me what does the yellow wire do at the ECM (this engine is a Carburetor model) and how does signal eventually reach the alarm buzzer assuming the sensor switch had been closed due to an overheated engine