So I went out for a night driving the Disco, and quickly started to notice the lights would get brighter when the RPMs climbed. I assumed there was an alternator problem, so when I got home I turned off and checked the voltage of the battery, 12.9V, perfect charge. Started her back up and checked the volts at idle, 13.6V, charging fine...

Then a day or two later I came outside with my dad to show him, but upon startup the red battery light came on indicating it wasn't charging, and sure enough the headlight was super dim and volts at idle were only 12.1V (after engine was off battery went back up to 12.7...

So what happened?! Why has the behavior of my disco changed from one day to the next??

One more thing to mention, at the beginning of the journey the left low beam burnt out, like right after turning it on. And towards the end of the night the left high beam went out... Makes me nervous that it was going over voltage as the RPMs climbed?

 

Okay, are you able to check the voltage while the Disco is moving, or just when it's standing. Quick option would be to run to the evil empire (Walmart) and pick up a power point (cigarette lighter) tester and see what the volts are doing while going down the street. If the volts are high (not a good thing with the thin wiring), the voltage regulator is part of the alternator, so you will need another one (AutoZone has a lifetime warrantied one for $185.00 plus core (That is much cheaper than the alternative. Had one go already due to a bearing which they replaced no questions asked, and the replacement has plugged along for months now with no issues). That's the route I went, and although I have the perpetual flickering lights (reason unknown), the volts are steady at 13.5. Lastly, invest in an Ultragauge. It will become your best friend!!

 

Sadly I can't run an ultra gauge, I have a 1995... I did recommend my buddy one based on this forum and he loves it for his saab.

As for measuring volts while in the car, not a bad idea...

What I don't get though is how the car was putting out 13.6V at idle, I left it alone for 48 hours, and then it had no charging at all!?

 

Another thing I just thought of, I recently disconnected the battery before having this problem, and this ground seems kinda loose, perhaps when pulling on the ground terminal I moved it. Would this ground cause charging problems? (pictured) it is the ground right adjacent to the batter connected to the main ground cable off the battery

 

Big yes, I just removed that cable cleaned everything made a difference

 

Ok I hope thats it... I kinda doubt it though cause the vehicle literally didn't move an inch from the one night it had 13.6V to the one it had nothing...

 

Just reread the original post alt may have just crapped out, no charging = no or intermittent tach signal
Had the tach bouncing on mine before

Still clean that cable, need a teach get one with lifetime warranty they suck

 

Yes exactly! The tach was dead too... Alt must have crapped eh?

What do you mean by "need a teach get one with lifetime warranty" I imagine thats a typo?

 

Auto correct sorry alternator, still clean that cable

 

Will do, I may try replacing just the alternator's voltage regulator, has anyone done that? My Disco only has 83k miles and the date code on the alternator seems to indicate 2003 so the brushes and all should be mint, the symptoms seem to indicate a regulator failure so by replacing just that and keeping the rest low miles oem perhaps thats a good thing?