I owned a 1979 245DL for many years, and while not encountering your exact problem, this might help.
The reason there is an apparent link between braking and the warning lights is that on braking there is a shift in the location of the engine relative to the car frame, larger movement if the motor mounts are seriously worn.
The motor mounts are not a problem needing immediate repair - worth checking out, though. Do this: with a cold engine, the distance between the bottom of oil filter and the motor mount below it should be large enough for ones hand to pass through easily. Easy check, just a little greasy.
There is a wiring harness that runs from the left side of the engine to a route under the front of the engine, coming up between the block and the alternator. That harness carries a wire to the oil pressure sensor (black), a small red wire to the alternator, and a large red wire to the alternator.
Due to age and rough environment the harness cover becomes brittle, the metal tabs holding the harness in place loose their protective coating, and the tabs abrade their way into the harness and the wires.
This creates a ground path for any wire so invaded. When the oil pressure sensor is grounded, the oil light comes on. When the thin red wire to the alternator in grounded, all the other warning lights come on. If the thick red wire gets grounded, there is danger. That wire is large and always connected to the battery. A grounding creates a serious fire hazard.
Engine movement makes contact between the invaded wire and the little tab to occur at certain times, not necessarily all the time. Hit brakes - engine moves a bit forward - contact made - lights come on.
Repair of the two small wires is usually to replace each wire from its end use connection (gray connector on firewall) down along the right fender and thence, with a lot of slack, to the using appliance.
Your first step would be to get under the car, drop the gravel protector pan, inspect the harness and the motor mounts, especially the right side.
Good Luck,
Bob
:>)
PS: If the thin red wire to the alternator gets an improper ground, all charging stops, too.
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