Keeps blowing fuse. A little help? - PeachParts Mercedes-Benz Forum

MeinGreaseCar · #1 05-28-2006, 07:19 PM

I'm at a loss.

I replaced my factory stereo. It works fine. I added in a 12V gauge, and a extra cigarette lighter plug for the XM radio. it works fine. All of that is on a seperate circuit from the one that blows.

When I turn on my lights. It blows the #1 fuse. Which is instrument lights, and right rear parking light.

The suspected culprit was the new stereo (illumination) input. I HAD put that into the former wire for the light inside the ashtray. It has since been removed and taped off.

I have one wire down there that used to be the ground? It's a brown wire with a large clip that used to ground the ashtray area I believe. Anyway, I have tried both grounding that clip, and unplugging the metal clip and leaving the end protected.

Still snaps fuses (even larger than rated) in a millisecond. I have tried removing the bulb from the parking light on that circuit. Still snaps fuse.

I tried putting a small piece of cardboard paper in the dash illumination rheostat (ok, reaching I know) and it's still blowing the fuse.

I see no chafing of the wrapped wire that holds the wire which used to light up the ashtray. That's my suspect.. I just don't know what it could be. I have the ends of it well away from one another... and it's taped off.

I suppose it could be something unrelated to the radio area.. but I don't like to believe in coincidences or double failures.

Ideas? Thoughts? Wild guesses?

Thanks
JP

Brian Carlton · #2 05-28-2006, 09:07 PM

Remove the radio from the console. Pull all the wires forward and be sure that none of them are pinched.

Try the lights again.

If the fuse blows, remove the radio connections from the harness. There must be an error in your wiring that has the 12V supply for the instrument lights connected to ground in some fashion.

The chances of a separate issue developing simultaneously with the radio installation are just about nil.

MeinGreaseCar · #3 05-28-2006, 09:27 PM

Thanks.. that was going to be my next move. After I recovered of course. You know.. you just get disgusted and have to step back.

If the harness is unplugged from the radio.. it shouldn't matter how it's wired.

It just doesnt make any sense though. The only wire that is in that area (i believe) that is hot with the headlight switch, is the ashtray light... isnt it?

JP

Brian Carlton · #4 05-28-2006, 09:58 PM

Quote:

Originally Posted by MeinGreaseCar

Thanks.. that was going to be my next move. After I recovered of course. You know.. you just get disgusted and have to step back.

If the harness is unplugged from the radio.. it shouldn't matter how it's wired.

It just doesnt make any sense though. The only wire that is in that area (i believe) that is hot with the headlight switch, is the ashtray light... isnt it?

JP

Yeah, I know the feeling........

If you unplug the harness, I agree, it won't matter how it's wired.

The center console illumination is fed from the #1 fuse. There is illumination for the CCU and illumination for the shift selector. You could have damaged these wires and one of them is shorting to ground. Look carefully for all the illumination lights in that area and make sure the wiring is intact and not cracked anywhere.

You may need to remove the CCU and check behind it for the problem.

MeinGreaseCar · #5 05-29-2006, 06:33 AM

Center console aka shifter light. forgot about that one.

It could be the culprit!

Thanks
JP

MeinGreaseCar · #6 05-29-2006, 07:38 AM

It wasn't the shifter. the wire for that light must be really buried.

It kept blowing fuses even with the radio harness unplugged.

SO... I figured that something had to be grounded that wasn't supposed to be.

I went over the wiring (I had a friend install the radio) Turns out that he had grounded a white wire with purple stripe. In fairness to him, it wouldnt have had current, as we were installing radio during the day. (with the light switch off obviously).

I would have thought he would have caught the color... and wondered. But alas.. it's fixed now. I tied it into the illumination wire on the radio.. and now it works like it should.

Thanks
JP

Brian Carlton · #7 05-29-2006, 12:48 PM

Good job. I was confident that it was related to the head unit installation.

Help is what we do here.

JHZR2 · #8 09-08-2009, 11:01 PM

An old one, but had the same problem today...

It seems to me that on my older w123 cars, the harness that attaches to the ashtray (and then goes to the radio) has a hot and a ground...

So Im working on an 85 300D, putting in a stereo. I took a harness from an 83 300D, and connected it into the power connector that would go to the ashtray... Red is hot, connect it to the switched hot, brown is ground, switch it to the body ground on the radio (already was usung a non-switched ground to the radio harness).

Lights had all worked, radio worked fine. Car was great all day. Come nighttime, turn on the lights and no cluster lights. Great. Found that fuse #1 was blown, and started troubleshooting all over the car.

Last ditch effort was to pull the radio, which was working. found out the hard way that the harness to the ashtray in an 85 300D has two wires, and they are both hot!

Not sure exactly how the ashtray actually grounds. It is kind of an issue... Anyone have any clue? The two wires to my ashtray (red and black with green, IIRC) have zero potential between each other, and are each 12V.

So I was using what would be a ground in any other car (I think) as a ground, when it was actually hot!

toomany MBZ · #9 09-09-2009, 10:09 AM

The ground may be the ash try itself grounding with the bracket you push it into.

Yak · #10 09-09-2009, 12:38 PM

The radio is poorly documented. You have several hot or switched wires connecting in, but they're not all shown in the diagrams and the diagrams are in different places in the FSM.

The radio has separate power for the light bulb (switched off the console light circuit from fuse #1) and power from the ashtray circuit (switched by the ignition switch and fuse 4) which also produces a switched output for the antenna. Wiring color codes are inconsistent. Depending on your switch positions you may test hot across several wires. And of course you have continuous hot from the battery for the clock (unswitched - and I'm unsure if this has a fuse in the fuse box- maybe fuse 2, or is fused at the radio).

http://www.tehnomagazin.com/Auto-radio-car-connector/Becker-Car-Radio-Wiring-Connector.htm

The light circuit IS hot even if the radio harness plug is removed from the ashtray connection, as is the radio clock power supply line. Theoretically, I guess you could "unplug" your radio from the ashtray (or pull fuse 4) and it will still light up and keep time but it otherwise won't work.

The ashtray itself is a circuit component, I think the chrome is ground and the copper/brass nub is hot. These connect up to the harnesses. In the radio harness pdf below, component #4 corresponds to connector C148 depicted above and below the ashtray in the radio errata pdf. Component #2 in the harness pdf should actually show four wires going to the ashtray (as depicted in the errata pdf): one hot wire going in (for lighter) and one hot continuing back out (for radio); one ground going in (lighter) and one ground going out (for radio).

I "think" the radio has an additional ground connection in addition to the ashtray, but that may simply be one more wire connected to the separate radio harness.

Depending on where you tested (before or after a connector) you may very well measure zero volts across different wires in the ashtray.