Si 10 Alternator on a Ford 850 not charging

[jaotguy]

the extra 2 wires are : light / exciter circuit and power for the alternator internal reg from the ignition switch (only power when ON )

the power when ON is the 12V for the comparator ( should I charge or not and how much )
the exciter wire and light triggers the alt to charge ..... power thru ignition switch to light then to alt and ground when not running , the light has 12 volts on one side and a ground on the other ..... when it starts to charge, the light now has 12volts on both sides so the light goes out indicating it is charging ...

 

[8N Ren]

This^^

 

[mitch becton]

just some fyi if the altenator is causing a drain it most likely the rectifier which in itself will contain from 6 to 8 or more diodes these when working properly will only allow current to go one way that is away from battery per say keep in mind when they work power only goes one way when they leak power back as sometimes called when the vehicle is shut down it will over time discharge battery to the naked eye you cannot always tell if the diode is bad or leaking fyi again a leaking diode can still work it can be tested with a multi meter fyi again if a battery is jumped off and the cables are hooked backwards in some cases it will blow the leads or diodes out of the rectifier also on any computer operated vehicle if some one pull the battery cables off while car is running it will do the same in most cases and as an extreme will blow out all the diodes the positive and the negative just had one this week off late model chrysler charger some mechanic pulled cable off while running ''BURNT ALTERNATOR UP'' this unit is only available from dealer at cost of over $500.00 so word to the wise never pull cable off running vehicle

 

[jaotguy]

pulling the cable off the battery removes the "base 12v" sensor to the regulator... this allows it to read + or - from the floating voltage you just created .... so if the voltage floats up and the regulator circuit floats up with it , it is still within "specs" and the alternator voltage keeps climbing until the voltage exceeds some component's tolerances ( ECU , RADIO, LIGHTS ,and or eventually the alternator itself ) and it happens QUICKLY.

in olden days , before sensitive digital components , the alternator test used to be ... start the car , turn on the lights and blower , then rev the engine up to 2000 RPM and then lift the positive battery terminal and see if the car died ... if it kept running , the alt was fine .... if it died, the alt was toast ...