"Charge" light comes on with other lights
 

I am replacing the warning light cluster in my 87 S4, and upon testing the new-to-me unit, the charge light illuminates when power is applied to any other bulb (minus brake and belts). Remove the charge bulb and all other bulbs still work normally.

I did a quick search and couldn't come up with anything. All solder points on the main plug are in good shape, and there is no corrosion that I can find on the board. Can anyone point me toward what I should be looking for?

Update. I went ahead and put it in the car to see what would happen. Clock works perfect (my reason for replacing the old one), but with the key on only two bulbs light up (I forgot which two, but the charge light is not one of them). Door light does not function, though it worked fine on the last unit. Oh well, looks like I'll be putting my gauges there instead of on the gauge cluster.

The meter fuse supplies voltage to the bulbs. What turns on the light is when a ground signal is then supplied to the individual wires or a ground is supplied to the Yellow/Blue wire, which happens to be connected to the charge light. So, w/key to on there should be a ground signal on the Y/L wire and this turns on all but one or two of the lights. The Y/L wire comes from the alternator warning light relay that is located in the CPU. Placing a ground on the wire at the CPU w/key to on should turn on most of these warning lights. The alternator is responsible for this ground w/key to on.

But when you turn the key on, before you start the car, all of the bulbs should light up, correct? That isn't happening on mine. The door light in the warning cluster also doesn't function anymore.

For the second time and w/feeling,

"So, w/key to on there should be a ground signal on the Y/L wire and this turns on all but one or two of the lights. The Y/L wire comes from the alternator warning light relay that is located in the CPU. Placing a ground on the wire at the CPU w/key to on should turn on most of these warning lights. The alternator is responsible for this ground w/key to on."

^ Maybe translate into steps or a course of action? Cuz I'm a bit lost too.

Are you saying maybe the relay in the CPU is working intermittently, and not providing a consistent ground? Your advice is well intended and accurate, but bring it down a notch for all of us.

OP, when you plug in the original warning cluster, do the lights work ok again as intended?

Test the diodes in your warning light cluster. Most digital multimeters have a diode test mode, sometimes it's built-in to the continuity test. A good diode will conduct one way but not the other.

If a diode goes bad, it can cause two lamps to light (dimly) when only one is supposed to be on.

It could be the relay or it could be the alternator or it could be the wiring involved. If you pull the two wire plug off the back of the alternator and w/key to on ground the White/Black wire (not the Black/White wire but the White/Black wire) and the idiot lights should come on. If they come on then the likely problem would be the alternator or the connection of the W/B wire to it is faulty.

If the grounding of the W/B wire w/key to on does cause the lights to illuminate then the problem lies downline from the alternator.

If grounding the Yellow/Blue wire at the CPU relay w/key to on causes the lights to turn on then the problem is w/the relay in the CPU (this assumes the alternator checked out okay).

The relay is powered by the meter fuse via the Black/Yellow wire. The Black wire is the ground. The White/Black wire comes from the alternator. And the Y/L wire runs from the relay to the idiot lights.

Thank you, satch, I'll test those when I get a chance.

Santos, the key-on bulb test didn't work on the old warning cluster either, but the door light still worked.