I replaced the alternator on my 07 LR3 3 times with final change using OEM Denso unit due to voltage spikes with previous 2 units. After car warms up voltage would spike to 17v causing all sorts of havoc electrically (dash flashing then going completely black, radiator fan running all the time, etc.). I traced the problem to the 3 pin PIG connector that plugs into the alternator. If I remove the PIG connector while the car is running, the dash comes back on, fan goes off and voltage drops to a normal 13.7v
The Pig connector has 3 wires...white with green stripe (positive on left side or plug), White with red stripe (negative in the center of plug), and Brown (positive on right side of plug). The PIG connector wires go into the main wiring harness. Does anyone know where the wires go to? I assume they go into the ECM or TCCM behind the battery? How do I tell which PIG wire is causing the short. I have a multimeter just dont know how to tell which wire is bad since 2 of the wires have power and one is neg. I can buypass the bad wire if I know which one it is and where it goes to.

 

 

so even with the denso unit the voltage is spiking?

 

WTF is a PIG connector? Have you looks at the ECM itself yet? There can be corrosion issues on the connects, especially if the engine bay is improperly pressure washed and or the battery is not vented properly. **** design really with the computers being where they are. Pain to dig em out, but might be easier than tracing the wires.

 

Thank you scooterforever for the schematicIt looks as though 2 of the wires from the Pig connector plug on the alternator are going into the ECM and one wire (brown) is fuse 20E at the junction box.

I can trace these 2 wires to the ECM plug by matching the colors of the wires and rewiring them. Does the schematic above show the actual PIN numbers at the ECM plug?

Lastly, the schematic shows at the alternator ALT CON as a positive White wire with a red stripe. The ALT MON negative wire is white with a green stripe. My current plug installed by the dealer has these reversed.
My ECM is brand new, cloned from the old one which turned out to be fine. Car has been garaged its entire life, no water intrusion whatsoever from the A pillar , fusebox back of glovebox.
I have tested these 3 wires from the Pig connector on the alternator, 2 wires on the outside of the connector are positive, wire in the middle is negative. How do i determine which wire is causuing the short?

 

Have you had this issue since the dealer worked on it? Generally wiring diagrams are pretty accurate. The connector is a known failure point - plastic + hot = brittle. I have a spare connector for that reason. So could the issue simply be that connector was wired wrong? I doubt is sense is the issue since it would trip an a charge warning and I *think* it is also the exciter wire so the alternator may not even work right at low idle.