well, my brake failure light has been on for quite a while now. apparently its because a difference in the levels for the two circuts dont match up, which would explain why my left front is ground down to the rotor already i suppose. but i was wondering what i need to do to fix this. and another problem that makes itself known every month or so, the left front starts sticking, and then the brakes go out all the way. i let it sit (or drive slowly) for about 10 minutes, and all works again for another month or more. its not a huge deal, except that i almost rear-ended someone the other day. so any suggestions on this would be appriciated too.

I had the same thing on my 83. Change the caliper. If $ is not that bad of an issue, change both of them. I also think that bleeding/changing the brake fluid helps after you fix the problem. Brake fluid is Hydroscopic (collects H2O). This gets into the caliper pistons and screws it all up. It's much better to solve the whole problem than just go after a symptom.
I got this info from a friend who helped me take care of mine. If I'm wrong, blame him. 8-)
Good luck.
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Yes, my new car is a 1983.

Sounds like the left caliper piston(s) sticking. Brakes "going out" maybe because fluid boiling due to overheating caused by friction. Raise left front, rotate wheel, probably seizing, if not-apply break pressure, rotate wheel, probably seizing. Your piston dust boots are probably gone. You could try cleaning/washing out the piston area with wd40 or maybe brake cleaner. And work the pistons in and out to free them. Or if that doesn't free them then another caliper.
Re: brake light. Imbalance in system. If the pedal was firm then it's not air. There's a trick where you loosen a brake line nut and tap the master cylinder (I think), retighten and the problem is solved. I'm not sure about this, though it has worked for me when I had a 145.

There's a trick where you loosen a brake line nut and tap the master cylinder (I think), retighten and the problem is solved. I'm not sure about this, though it has worked for me when I had a 145.

Or it might be the brake differential switch unit.

You've got a bad caliper. Change it SOON before you get in an accident!

I can't say for certain that this will fix the warning light but it's definitely not helping. I know it's a pain to bleed brakes in a 240, and sometimes you can't get a proper bleeding due to trouble in the junction block, but you HAVE TO fix this.
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Rob Bareiss, New London CT ::: 86 244DL, 87 244DL, 88 744GLE, 91 244: 808K total