Battery Alternator light

[BlueDog]

The battery alternator light on my '89 Jetta begins to flash rapidly. It comes on bright and steady when I start the engine. Kick the accelerator to excite the alternator and the light goes out. Now it has started to blink when driving down the road at most any cruising speed. The light goes back off when just idling. Goes back to blinking when I speed up. It's not a steady blinking. What's the cause of this? How do I fix it?

[bscutt]

Would be nice to see what your voltage is when it blinks - any way you can rig up a cheap multimeter to a 12v line? Harbor Freight's chespest meter works reasonably well for automotive troubleshooting. Could just be a loose ground or could be signs of the alternator going bad. Check every connection you can find and see if anything is loose or corroded

[BlueDog]

I cleaned all the ground wires I could find. Also cleaned the neg and pos at the battery. Nothing changed. I could connect my multimeter with the hood up and increase the RPM while in neutral and see what voltage reading I get. But I didn't read your post before I removed the alternator. I suspect the brushes are worn out and I plan to take it in for a rebuild tomorrow.

[82vdub]

You may have an alternator going bad, but you could also have a wire that's developing a short. These are little rattle boxes, and wires do have issues from time to time as they flex. So each connection may be fine, but the issue may be be at location where the wire terminates to the connector as that's flexed over time, or even farther up the wiring harness.

[vwtyp133]

x2 for the 'rattle box' comment by 82vdub!

OTOH, seeing that Jack (owner of this site) doesn't seem to list/carry alternator parts, you might note that (competitor's name removed by moderator) (located in Madison, WI ?) sells the entire voltage regulator (including new brushes!) for the Bosch alternator for just under $9.USD. Easy plug n' play replacement. I'd be tempted, even if just to have a spare VR on hand!

Best wishes finding the gremlin(s).

[BlueDog]

Dropped it off at the rebuild shop on the way to work today. Thought I'd drop it at the back door and then call them about it when they open at 8AM. I was surprised to see the main repairman was there already before 7AM. He put it on the tester machine right away and saw it doing erratic voltage read-outs. So he pulled the brushes cartridge and showed me that where the brushes ride on the armature one side was shiny and the other was dull with deposits on it. He says that's the problem and he can fix it to work like new again. At this stage I'm optimistic.