L light question

[Philbert]

So, my L light has started flickering right around 2500 rpm. This happens on acceleration and deceleration. I've cleaned contacts and grounds at the alternator and checked belt tension. All seems in order. I did discover a loose connection at the ignition switch (one of the green wires) and fixed it. No change... Anybody have any thoughts about what might be going on? One more thing- as the motor warms up it gets better but doesn't go away. My electrical knowledge is pretty limited, call me mystified in Seattle...

[wegweiser]

Make sure the wires are solidly attached to the female connectors INSIDE the 3 pole plug on the back of the alternator *AND* the similar plug on the voltage regulator.

I had one of the wires get loose about 18 months ago moments after I arrived in NC for The Vintage event. Did a temporary fix to get her home, then ended up replacing about 18" of wiring to FULLY correct the problem later on. On a tii it's a PITA to reach that stuff with a soldering gun, and it's often bathed in oil from oil changes and engine leaks.

I didn't realize there was a recurring problem a few months ago, because the bulb on my dashboard had just burned out....nearly left me stranded as my battery drained while I drove....which is what led to the complete and thorough replacement of the section of wiring.

The correct "snap in" captive female connectors are available from BMW. 61 13 8 608 021. Check these connections and test the output using a multimeter before replacing the alternator. Adding an external ground from the back of the alternator housing to the engine is always a good idea, too.

This photo is of the emergency fix I had to perform a couple months ago. Stripped the wire with my teeth, while my face was pressed up against the oil pan in a parking lot. Not fun....and totally avoidable!

[andrey]

Also check that the alternator is grounded properly, I had a similar issue when the ground got disconnected. If the alternator mounts solidly to the bracket (no rubber bushings), you just need to be sure there's a ground strap for the engine block to the body and/or battery negative. If it mounts through rubber bushings, you need to make sure there's a ground wire (from the ground symbol stud, not just anywhere!) between the alternator and the engine block and/or battery negative. Basically look for some loose or disconnected wires first

If the alternator is starting to make noise or the pulley is wobbling, it's time to have it replaced. Also double-check the V-belt tension while you're starting at that stuff.

[Philbert]

Thanks guys, for the suggestions. I continue to be amazed how helpful FAQ folks are. I,ll do some more investigating tomorrow. i,m still a bit perplexed by the specific rpm thing, maybe there's a loose connection that only shakes at a certain frequency...? Will report back.

[andrey]

Yeah, the RPM thing may be that or it may be something in the alternator failing and being apparent at particular RPMs. Hard to tell before you look closely.

I'm also in Seattle so if you need a second opinion or something, let me know and we can troubleshoot it together.

[c.d.iesel]

dead diode(s) in alternator

= replace alternator

[andrey]

Speaking of which, I'm pretty sure I have a spare (used) one sitting around here somewhere. I'll try to find it for you tonight in case you need it (no charge, it'll be less crap sitting on the shelf)

[Mike Self]

There's supposed to be a wire bail to hold the plug in place and it's often missing. Make sure you have one, otherwise that plug is gonna vibrate and fall out, or at least work loose on a pretty regular basis.

Dunno if the bail is still available as a spare part, but you could make one out of spring steel wire...

mike