Intermittant dim battery light puzzle

[Sergey]

Hi all,

I have a '95 ti w/205K on it and it just gave me its first electrical puzzle. Everything electrical is original except for the battery that's 2 years old. Battery terminals are clean and battery cables are tight.

When I turn ignition on, not starting the engine yet, the battery light comes on dimly, at about a third of its usual brightness.
Once the engine is started, the light usually goes off. There was one time when the light stayed dimly on for a couple of miles, then went off.
Sometimes, if I leave ignition on, without starting the engine, the light would go from dim to bright on its own.
Except for this bizzare battery light, everything electrial works fine, the cars starts and runs.

Voltage checks that I made:
battery - 12.6
B+ alternator terminal - 12.6
D+ alternator terminal - 7.8 (ignition on, dim light)
D+ alternator terminal - 1.3 (ignition on, bright light)

This D+ voltage got me puzzled. Bentley says there's supposed to be "battery voltage" on D+ with ignition on, I assume I should've seen slightly less then 12.6 there. I pulled the instrument cluster and figured that the voltage drop happens across the cluster, that is it's close to battery voltage to the lock, across the lock with ignition on and into the cluster, but I'm seeing those 7.8 or 1.3 at any point after the cluster.

I also did the usual crude tests of the alternator when the light was off and got about 14.1 with no load and 13.9 with some load (headlights, defroster, blower) across battery terminals. No changes as I revved the engine. I once caught the dim light in the act and measured 11.5 across battery terminals.

I also did a static draw test and saw good solid 15 mA.

What do you guys think this is? I saw the 11.5 on the battery with the engine running and the battery light dim, so that suggests that the alternator is going, which wouldn't be surprising. But what about that D+ voltage? I really don't want to need a new instrument cluster

TIA,
Sergey.