Purpose of white LED lights inside Wolcott amp.

I can't think of any other reason for a light like you describe. Even more odd is that its not in the manual. Check the amp again and look for any type of adjustment. Sometimes tube amps set their bias up so that 1 adjuster is used for 2 or more tubes (on the same channel). I guess it could be something like a power light. If the led on the other side of the amp is not on, the bulb may be bad.

I forgot to mention that you should swap the tubes position. Take the tubes in the right channel and move them to the left channel. And move the left tubes to the right channel.

I don't know the amps but some circuits use LEDS as cathode bias voltage droppers. Their low impede nice means they don't need a bypass cap.

Gentlemen,
Thanks again for your ideas and input.
I have heard back from Pat McGuire at Wolcott and the riddle is solved.
As is turns out, when I had sent this amp in for a check up a couple of years ago he custom installed the LEDs as servo circuit "out of balance" indicators for my 6922 input tubes. There are two input tubes per channel. After instaling a couple of different input tubes the lamp in now off and the the amp (and the Quad ESL 989s) are 100%. Turns out he personally built this amp and it is one of five.
Wolcott kept three. Henery Wolcott (rest his soul) used two for reference amps. Pat uses one. A well known audio reviewer bought one after reviewing it, I have number five. The Wolcott P-120S is rated at 125 watts per side powered by 8 EL-34s. Self biasing with unlimited dampening. Power consumtion is only 100 watts, so low heat emitting (for a tube amp) and all in one tidy 70lb stereo amp.
Wolcott and Pat McGuire are still one hell of a electronics company.
Hard to find a Wolcott on the used market. All I can say is I'll never part with mine.

Have you contact Wolcott Audio? I believe the LED comes on indicate a bad tube.