MisterBLC

Folks,

Just finished dropping an LS6 from a '04 CTS-V into my '85 Volvo 740, but I am having a weird electrical issue with the alternator wiring and the dash indicator light. The Volvo dash using a traditional charging system with 12v switched being sent through a indicator bulb and then sent to the alternator to excite it. I am running the stock '04 CTS-V alternator (part number 25750935) with has a 4 pin connector with only 2 pins populated, an "L" and "F" pin. I have the dash indicator light connected to the "L" pin on the alternator...the "F" pin is disconnected. The alternator does appear to charge fine when the engine is running...I see 13.8-14V on the output. The problem is that intermittently, when I put the key in position 2 but with the engine NOT running, the dash indicator does NOT come on. Other times, the indicator light comes on just like it is supposed when the key is in the #2 position but the engine is not running. My guess is that I have the wiring wrong or that my alternator is supposed to be getting some sort of signal from the ECU to control it. Has anyone else run into this issue during a swap? Do I need to connect the "F" pin to something to prevent this behavior? Any help would be greatly appreciated!!

One note...I am running an aftermarket ECU, so I can't use the stock GM computer to control the alternator.

Thanks!
Brian

Michael Yount

iTrader: (1)

82 242 w/Crate Ls3 w/stock E38 08 Corvette ecu and 145A Escalade alt. It takes a 4 wire plug with 3 wires connected. Operating from memory - the S wire is a sensing wire - I simply connected it to the output stud. My recollection is that both L and F went back to ECU for control. I tapped into one of them - whichever one goes to ground when the alt isn’t charging. I had to separate the alt light bulb from the printed circuit that controls the dash lights because of common grounds. I connected one side of the alt light bulb to switched 12V+ from the fuse box. The other side of the bulb goes to that alt wire that’s grounded when the alt isn’t charging. So with ignition on, engine off the alt light lights up as it has 12V in one side and ground on the other. Once engine starts and alt begins charging - the alt light now has 12V on each side - and the light goes out.

Maybe something in there will help with yours.

aknovaman

iTrader: (7)

Bulb connects to the "L" alternator terminal then to switched ignition. Terminals are labeled in small letters on the internal regulator and can be seen by looking at back (engine side) of alternator.

Michael Yount

iTrader: (1)

Does L also go back to the ecu in the oem application? I know in my PSI harness it was part of the harness that originated there...no idea what for though.

MisterBLC

This is what I have now, but I am getting the strange dash behavior...which is why I have been wondering if I need to do something to tie off the "F" pin.

aknovaman

iTrader: (7)

The F terminal has nothing to do with your issue, IMO.