Did my alternator just die?

[Bammo68]

OK update time - issue seemed to sort itself out as soon as I ordered the replacement alternator but when I fitted the new alternator and took her for a good thrash the check gauges light came on again and voltage output dropped to 12.1V again after about 5 minutes of driving.

So, whatever is wrong, it doesn't seem like its the alternator, something else is causing this issue.

Any ideas?

 

[oldjeepman]

Have you checked/replaced your battery cables?

 

[Bammo68]

SOLVED!

Wow, sometimes I look at how long it takes me to solve a simple issue like this and I wonder how I managed to ever get through an Engineering Degree....

I should have just stared at the wiring diagram in the FSM and thought this through but instead I kept looking at YouTube videos and winding up at the "PCM is faulty and needs to be repaired" outcome. The generator control circuit that goes from the PCM to the back of the alternator has +12V on the solid green wire and a PWM switchable ground on the GR/OR wire (on my 99). I had previously grounded the PWM switching wire noting that many folks complained of a dodgy ground here but that didn't work. I then back probed the +12V wire out of the PCM and hey presto, 0V. Why didn't I check that first? Because watching YouTube sometimes make you dumb, that's why.

+12V coming out of the PCM though so clearly this was a wiring fault which makes sense given I had moved that harness around a lot whilst I did the engine swap. Lo and behold, the main wiring harness connector (connector C103) that sits above cylinder #6 was not fully seated properly and the red latch wasn't closed all the way.

So now I have a nice new alternator and a spare on the shelf and 13.9V back into the battery - ripper! Just embarrassed it took me that long to test the right thing... you really do need to be in methodical mode when fault finding sometimes - jumping to a solution before fully and accurately identifying the problem was my rookie mistake.

Thanks for the help along the way...