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2003 7.3 , Installed a reman alternator from oriellys due to old alternator charging at 12.6 volts idle and it would emit a buzzing sound when truck was off and key was out of ignition...figured old alternator was bad so got a new one and repaired the connector wires due to the previous owner repairing them with electrical tape and not butt connectors. Installed new alternator and as soon as the batteries were reconnected the reman alt started emitting the buzzing sound again. Started truck and at idle was charging at 12.6 volts still , so the reman is having same issue as old one, checked wire diagram and connector view of ford manual to make sure wires were correct and took voltage measurements , My light green and red wire was battery voltage all the time regardless of key on or off which the diagram shows it being hot when key on , checked fuse to the lg/rd wire and it was good removed fuse and still getting battery voltage to lg/rd wire regardless of key , my yellow wire is 0 volts with key off and battery voltage with key on , when lg/rd wire is connected to alternator it starts buzzing and when contacted with a ground the buzzing quits. Also performed diode test thinking maybe regulator on reman alt was bad but the test was good and only flows one way. With truck running if I have none of the wires plugs in on the alt connector , the alt will charge at 12.8 volts , if I plug just red wire in while running the alt will charge at 14 volts and will drop down when loaded but come right back up between 13.8/14 volts , as soon as yellow wire is plug alt charge drops to 11.8-12.5 volts as if the alt is not charging anymore , as soon as yellow wire is unplugged with red wire plug in it shoots back to around 14 volts…also when yellow wire is plugged in the idle sound changes and when yellow is unplug idle returns to normal sound , So unsure if bad alternator if I have wire issue or other issue. Alt buzzing is also killing batteries , if wires are left disconnected and buzzing is not happening the batteries do not discharge . Alt can still be returned and exchanged if need be. Any insight would help , thank you !
LG/RD Key Off Voltage LG/RD Key On Voltage Yellow Wire Key Off Voltage Yellow Wire Key On Voltage Assume wiring is correct
According to that diagram the yellow should be a constant 12v.
my assumption too but only gets b+ when key is on , the lg/rd wire gets b+ constant for me , which is backwards from what the diagram shows…plus my connector view doesn’t even have a yellow wire in the diagram
The light green / red stripe wire is the Ignition circuit.
It should have 0 volts with Key Off Engine Off
It should have between 1 to 3 volts (typically 2 volts) with Key ON Engine OFF
It should have between 13 to 15 volts (reflecting the output voltage of a working alternator) with Key ON Engine RUNNING.
The yellow wire has likely been substituted for what was originally an Orange / Light Blue stripe OEM wire.
The fact that a different wire color is present, combined with unexpected behaviors manifesting in the system, is sufficient cause to peel back all of the wire protective loom until the splice is found where the substitute yellow wire was introduced.
When looking at the connector, the middle wire isn't used.
Other than the light green / red stripe Ignition wire discussed earlier above, the only other active wire routed to that 3 pin connector is the battery Sense circuit.
Regardless of what color it is, the Sense circuit voltage behavior under the three key scenarios above is as follows:
It should have 12.6 volts (assuming the battery is fully charged) with Key Off Engine Off
It should have between 10.5 volts to 12.6 volts (depending on how long the key has been on) with Key ON Engine OFF
It should have between 13 to 15 volts (reflecting the output voltage of a working alternator) with Key ON Engine RUNNING.
Investigate whether the Ignition and Sense wire positions were inadvertently swapped during one of the times that the wires were repaired.
