mccsix

My 2006 CLK 350 has gone evil on me. It sits for a long time and when it's time to go, doesn't start. So it gets it's batt replaced a lot because they die a lot. Dlr keeps replacing them and the car runs good till it sits up again, ( I know it should be on a trickle charger or disconnected).
This time however when I put the replacement batt in, all hell breaks loose...lights comes on, fan comes on high, wispy smoke, hot batt wires and the switches have no control over anything. I quickly disconnect the batt.
I know there is a direct short somewhere, probably in some module, but I don't know where to start.
Can anyone help before we go up in smoke

?

Fatz

I can't imagine something shorting while sitting with a decaying battery. If it has been sitting again, maybe some critter tried living in some cozy spot of your car. I would open all electronics enclosures and inspect. I assume you didn't reverse the battery connections.

dfrois

One possibility is water ingress while stopped. Has the car been out in the open, or in a garage?

As for troubleshooting, the only thing I can think of is pulling all the fuses, before reconnecting a battery, and then inserting the fuses one by one. You should, obviously, be sure that the battery is in good condition, and charged, before connecting it to the car.

If the battery shorts with all fuses pulled, then the short can only be in the few direct connections to the battery - starter cable, some ground cable shorting within the battery box connections, something like that.

If it were me, I would pull all the accesible covers and panels, everywhere (engine compartment, cockpit and trunk) and take a good look with a powerful flashlight, looking for odd things, like dampness or damaged wires or plugs - before connecting a battery again. I would look underneath the car too, if possible.

Good luck. Let us know how it goes.

mccsix

Thanks for the help guys. The car is inside and dry in the garage.
What i"m going to try is disconnect (don't know how...yet) all the SAM/fuse boxes and see if the short is still there.
Then one by one re-connect the boxes testing the batt each time till I can ID the bad sam/fuse box.
If that doesn't work I guess it's off to the shop.