Here's an interesting one for 124's
 

'86 300E; my s/o tells me she had to slam on the brakes as someone was cutting her off - purse fell on passenger floorboard and all the dash lights came on and do not go off (unless the car is off). Alarm is disconnected. Ideas?

Overvoltage relay. Might be something else, but the OVR seems to be a consistant factor in electical glitches. It lives behind the battery, and has a fuse on top.

Check the alternator. What you are describing sounds EXACTLY what just happened to me. Simply get a multimeter and put the + on the + side of the battery and the - on the -. It should read (idling) between 14v and 15v. Then turn on the lights and see how much it drops.

Sounds like an alternator problem, or you battery terminals came loose.

the car is doing the symptoms of OVP failure, starts and dies; I have one coming in tomorrow. Now I would like to understand what happened? How does slamming on the brakes cause this? Is it that the alt. is weak and the sudden reduction in engine rpms caused a sudden drop in voltage? And how would that not just blow the fuse in the ovp?

i have had two go... no fuses blown..

pull it, shake it... if you hear some beads or any noise... it is shot. case dismissed.

I have a dumb question: Is the serpentine belt intact?

Yes the belt is good, thanks for asking, sometimes I miss stuff right in front of me. The alt. is weak and I will replace it and likely the battery too. What about the technical explanation of how all this happens with just slamming on the brakes? I would like to learn as well as replace parts. David

Dash lights come on when the related components are not operating/receiving voltage. A weak alternator will cause that. Or, more likely, worn voltage regulators within the alternator (an easy remedy). But I am more fixed on this:

You don't need to slam on the brakes for this to happen. My jackets, cell phone, groceries, etc., frequently slide onto the floor when I am braking.

It has been my experience that, when people damage other people's property, they tend to obscure or omit relevant facts when describing what happened. Perhaps you and your S.O. should have another conversation, to see what forgotten or overlooked details are suddenly remembered. ;) (A few glasses or wine, rum, vodka, or some other "truth serum" may prove useful.) :D

There is no doubt more to the story; unfortunately she is (no offense intended here) Polish and can drink me under the table; if I had some LSD I would have a chance; I sold my ML because there were too many 'incidents' and that damn thing is real expensive to keep up (If anyone finds a black opal passenger side mirror let me know, it should be intact as 'it just fell off the truck' and watch those tires folks because it is little known that they can blow out in a near perfect V shape on the sidewall. I am pulling the vr off the alternator tomorrow and will try that first, have a new battery in the Porsche so I will swap that out. Love these cars, this one has over 214K; I will do some minor body repair and reshoot it this spring. Thanks for the input.
I should do a disclaimer here: she is and has been a great companion over the years through several major tragedies and is a great mom to our four daughters; we really should get married someday. It has been interesting living with five women, I had two male cats but they got hold of them and well . . . you know what happened.

The problem was a bad alternator; PepBoys rebuilt Bosch, lifetime warranty; they switched out the resistor and pulley; $119 with core.

Oh man you serious? I paid $192 for mine with core (yes mad!!)...I thought I got a good deal too.

Glad to hear you got it straightened out.

For those who read this thread later...

Almost always the problem is the voltage regulator/brushes in the back of the alternator.

Two screws and about $25 gets it done.