Preinsch

2003 C32 has a new alternator. However, the battery is not charging. Started vehicle and removed positive cable from battery and the vehicle turned off. This should not happen because the alternator will continue the positive charge without the battery. There is a hidden fuse (150 amp+)somewhere in the car that the alternator cable leads to. that subsequently leads to the second cable attached to you battery terminal. I can't find this fuse. Any thoughts!

amgrobaspach

May or may not be the problem but I had a similar experience with my C32, Battery completely dead, Battery wouldn't charge, Replaced alternator and same thing.

In my case it turned out that My passenger seat was draining my battery and alternator somehow. After disconnecting the power module to the passenger and replaced with new battery car worked fine. Like I stated before this May or May NOT be the case with your situation but I just thought I should throw it out there as a possibility.

Preinsch

I appreciate your information and I have checked the circuits already. On some Mercedes it's called The X 4/10 fuse unit where are the lead from the alternator goes through before it returns to the terminal connector on the battery which should have two red cables attached to it. One of those cables goes to the positive side circuitry of the engine and the other disappears into the firewall to that so-called alternator fuse. The fuse looks like a pinky bandage and has holes on each end and we'll have a printed amp rating in the middle. Headset cars is located under the footboard of the passenger side. On others it's on the floor near the emergency brake pedal. On the C32 I've checked both areas with no luck. I think it may have a lead going up in the console underneath the ashtray. I see two cables coming through the firewall and one of them goes all the way to the back trunk fuse box and the other one disappears up into the console. I'm hoping someone sees this and says it is under the ashtray. Thanks for your information.

latemodel21

I looked this up in the WebETM and this is all I found (see pic).

According to what I found there, most models of the W203 have a 175 amp fuse (f56) (somewhere) in the cable running from the ALT to the starter (oddly, no fuse shown on M113 models). Normally the "star finder" in the ETM will show you a picture of the actual location of a component (f56 in this case) but oddly, in this instance it merely says "image not available" and "F56
Starter, alternator fuse (in wiring harness)"

I suspect that you can check it by testing for continuity between the connection at the alt and the connection at the starter (you will likely want to remove one end while you do this check to eliminate the possibility of getting a misleading continuity reading through the ground-path).


hope that helps,
Chris

Preinsch

Wow thank you so much. I had been looking all over to find the schematic. Yes both cables from the starter and the from the alternator run into the firewall so I'm suspecting that the last two places I have to search I will find it underneath one of the seats. Just like other schematics the picture doesn't tell you how long or how far away the actual connection is. You can't just look under the seats either without taking them out. But your information sounds right on to what I'm looking for. The car is telling me that circuit flirty has low voltage and I looked it up and that's the same circuit that I'm looking for. Once I solve this I'll post it for other members in the future.loop

latemodel21

I would think you would most likely find it in the passenger foot-well. Many mercedes vehicles have a panel under the carpet (where it angles up to the firewall).

good luck,
Chris

Preinsch

Thanks guys for the search tip, however the passenger side both the footwell and Under the seat and under the carpet did not show anything. However inside the wiring loom I see that in front of the seat on the passenger side both red thick wires go acrossed and up over the dash by the ashtray and back down on the other side. So now it's a search under the driver side footwell and under the driver seat. I'll keep you posted and sorry for the delay as I had to go wood cutting yesterday. Thanks, Petey

nicks158

Hi Petey,

I just had this same issue. Turned out to be a non-serviceable diode within the alternator. If you have continuity between the alternator lead and the positive cable of your battery, then you do not have a fusing issue. To my knowledge, the only large fuses on our cars are the ones that reside in the x4/10 unit right by the battery (black box with (+) tab on it for battery charging.

At fist I just replaced my voltage regulator, thinking worn out brushes were the issue, but I was sorely disappointed when I found out I needed a new alternator.

The new alternator did however solve my issue.

Hope this helps!

Nick

Preinsch

Nick thanks for your information and it seems to be very close to my problem. I did cited to go into the X 4/10 unit after I found it being mounted right next to the battery in the black box as you stated. It appears that the heavy gauge cable had a break in it causing the two hundred amp fuse to blow when it grounded out. I replace the red cable yesterday along with the fuse and started it up. Before I was getting SRS and abs and under voltage on circuit 30 and all those have gone away. The alternator is new and charging the battery fine now. The one advantage I have is I know exactly where all the wires run in there looms now under the carpet. This is not without a lot of painstaking research. It did give me the opportunity to do a lot of continuity checking so that I didn't have to pull out panels again. My C32 is zooming across the road again. Petey

Preinsch

For anyone who has a C32 AMG the location of the X 4/10 unit is mounted in front of the battery and has the red cap positive jumper cable post located on top. It is very difficult to get into this box and takes a lot of crying and opening glued shut areas in the back on the engine side of the black box you. There are two full of matches that need to be Pride up completely on the top on each side of the Red Cap. It has tab Clips around it that all need to be unlatched at the same time. This took two people working side-by-side to accomplish and I broke one of the clips. But inside there are four fuses that are called pre fuses for the starter alternator and other components. You can test continuity acrossed all the fuses to narrow down which one is blown, if any. If none of the fuses are blown then there is a deeper problem such as and alternator or a starter issue. Hope this help somebody in the future.

Hydro Tsunami

Hello. I replaced my alternator and ground wire got real hot melting it a little bit.

New alternator and now it cranks no start. How do I check the fuses in the prefuse box and know if they are blown or not? I have opened it and see the cables.

Theres very little rust it looks like on some but very little. Little specks of rust. Im pretty sure I have the same issue and need to replace my ground wire.