One of the nice things about a good circuit analysis is the ability to use the car itself as a troubleshooting tool so that's what we'll do.
That your alternator works has no bearing on the indicator problem because the Type M regulator's regulation and warning lamp circuits are independent. That's why you may be charging OK but can still have a leaky warning light circuit. If that's the problem you'll need to replace the regulator. It's not hard to do but verify it first by pulling the charge fuse. Remove the 7.5 amp charge fuse *with the engine running* (removal of the fuse will not effect the charging system's performance) and see if the dimmed warning lights go out.
Also try unplugging the lamp sensor box to see if the dimmed indicators go completely out and be sure the parking brake light goes from bright to a little brighter when the brake is applied with the key on and *engine off.* All this will tell us where the leaky ground path is originating from.
The diodes you mentioned in the combo meter are for isolating one indicator from the other so that a valid ground from the light failure box doesn't illuminate the brake light and vice versa. It's quite possible for them to cause this problem but in addition to one or either diode being shorted something else would have to be supplying the ground path. We need to establish if it's the voltage regulator, light failure box, or handbrake circuit.
If any of that doesn't makes sense say so and I'll try and explain it better
