Instruments panel lights up when brakes applied?

[wwotr]

I've got my 72 GMC Shortbed Fleetside at the shop.
One of the things my mechanic asked me was to post on the board about this problem:

When the lights are off and the Brake is applied, the Instrument Panel Lights- Light up.

Now they also go on as they should when the Headlight switch is pulled out and I notice,
NO DIMMING of the Instrument Panel Lights when the Brake is applied.

I seem to remember a similar problem on my 67 C-10, but that was so many years ago.............. (and another Mechanic).

I thought some of the better informed 67-72 owners might know...like "
Oh hell yea thats a common problem on those Trucks. Just take XXXXX and do XXXX and your good to go".

I wanted to hopefully find out what it is a have my mexchanic remedy it BEFORE I pick it up on Monday.
Any Links/thoughts/opinions would be appreciated!

Roger
"RATIKLE"