83 300sd Brake Lights Blown Fuse help please - PeachParts Mercedes-Benz Forum

ShadeTree300SD · #1 03-13-2012, 07:10 PM

Hello all,

I'm a newbie to this forum so first let me thank all for creating and maintaining. I have a 83 300sd

Issue: Fuse for brake lights continues to blow. I can change the fuse and in the driveway do everything to try and make it blow with no result and the brake lights work no problem. I take it out on the street and fairly soon when applying the brakes the fuse will blow. The tach, fuel gauge and temp gauge are on the same fuse. Couls it be the brake switch or is it most likely a grounding out wire somewhere?

Thanks for any suggestions you might have, and thanks again for the awesome forum!

Craig

Yak · #2 03-13-2012, 07:33 PM

Aftermarket radio? If so, maybe a messed up wire with the radio, the antenna or an amp, if there's one in the trunk.

It blows with the brake, though? Not a power window, or a turn signal action? You're not messing with cruise control are you?

Triple check you also have the correct type of brake bulbs. If you use an HD bulb they can partially melt your socket.

Welcome to the forum.

Tip: if you're working with a fuse, ID the fuse(s) you've worked on because sometimes there is more than one fuse for a circuit. E.g. windows have a fuse for the relay, and a separate fuse for window motors.

ShadeTree300SD · #3 03-13-2012, 07:52 PM

Yak, thanks for the response. Original radio with a non powered fixed antenna. At first I thought it was caused by using the turn signal switch but now I'm sure the fuse only blows when I apply the brakes. But not all the time, can't duplicate in the driveway. Cruise control hasn't worked in years. I looked at the bulbs and I'm not sure if they are the right ones but I'm on my way to get 2 new correct bulbs. I just drove about a half mile and couldn't get it to blow. The fuse in question is the 8amp in socket 12.

TnBob · #4 03-13-2012, 07:56 PM

Proper fuse size should be on the paper insert in your fuse box cover.

ShadeTree300SD · #5 03-14-2012, 10:44 AM

Another clue to the investigation! Sometimes when I start the car for the first time in the morning the wipers come on all by themselves. They wipe a couple of times then stop. I put in new correct bulbs late yesterday and drove a little and the fuse didn't blow. When I drove it this morning it took a couple of brakings the then the fuse blew again. Any suggestions??

oldsinner111 · #6 03-14-2012, 10:52 AM

they say to use German bulbs

JamesDean · #7 03-14-2012, 11:29 AM

Quote:

Originally Posted by ShadeTree300SD

Another clue to the investigation! Sometimes when I start the car for the first time in the morning the wipers come on all by themselves. They wipe a couple of times then stop. I put in new correct bulbs late yesterday and drove a little and the fuse didn't blow. When I drove it this morning it took a couple of brakings the then the fuse blew again. Any suggestions??

Perhaps you have a wiring issue with the turn signal switch. Perhaps you should take the carpeted panel off and look upwards to where the switch connects in to the harness, maybe something is a miss there.

ShadeTree300SD · #8 03-14-2012, 11:57 AM

JamesDean thanks for the response. Good idea, I've been suspect of this because several years ago the combination switch was replaced and I thought just maybe something was going on there. That might explain the wipers coming on randomly. Could a guy unplug that combination switch and then see if the brake lights blow the fuse?

JamesDean · #9 03-14-2012, 12:23 PM

I dont see why you couldn't unplug it and see what happens.

Don't do it at night, as I think you might lose regular headlamps. I recall someone saying that they'd lost low-beams due to a bad switch.

ShadeTree300SD · #10 03-14-2012, 12:23 PM

Ok, I removed the panel under the dash yesterday thinking but unknowingly that the problem might be the brake switch. So just a few minutes ago I disconnected the combination switch plug and put in a new fuse and drove down the street. By about the 3rd braking the fuse blew once again. Would it be safe to say the problem is not the combination switch? Could it be the brake switch? It's sure looks fun to change that thing!!

JamesDean · #11 03-14-2012, 12:32 PM

Hm, well yes I think you've eliminated the combination switch.

If you're in a low-traffic, quiet residential area (I live in a one-entrance developement with no traffic) I'd suggest unplugging the brake lights in the rear and driving again and seeing if the fuse blows.

ShadeTree300SD · #12 03-14-2012, 12:58 PM

Ok, I took your suggestion (thank you) of unplugging the tailights. I unplugged both taillights and drove around my quiet area and did not blow a fuse! Does this mean I could eliminate the brake switch as an issue? Then I hooked up the drivers side tailight and drove around and no blown fuse. Then I dsiconneted the drivers side and hooked up the passengers side and could not get the fuse to blow! I thought I might be able to isolate the problem to one side or the other. Maybe that is over simple thinking!!

oldsinner111 · #13 03-14-2012, 01:22 PM

American bulbs are bad for that I've heard.I replave all my bulbs with LEDs.lower wattage,and brighter.The europeon bulbs are called osram.

JamesDean · #14 03-14-2012, 01:25 PM

So now the question is this: Is the problem in the tail-light or did just removing the additional 3.5 amp load (brake lights) from the circuit just allow whatever is causing the problem to draw current and not blow the fuse.

The FSM says:

JamesDean · #15 03-14-2012, 01:27 PM

Quote:

Originally Posted by oldsinner111

American bulbs are bad for that I've heard.I replave all my bulbs with LEDs.lower wattage,and brighter.The europeon bulbs are called osram.

I've never heard of this.

I've always used Sylvania or Philips bulbs in my cars, more accurately whatever the parts stored had in stock.

Sylvania/Osram are the same company.