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rpmdiag, Tech and Instructor
Category: Mercedes
Satisfied Customers: 8151
Experience:  Since 1975
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I have a 2003 SL 500 I replace the battery a few weeks ago I

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I have a 2003 SL 500 I replace the battery a few weeks ago I now have no power to anything the transmission is locked so I can't have it towed can you help me
JA: Is the power loss consistent, or does it fluctuate?
Customer: LI have no power to the ignition switch or anything else the windows are stuck down but the door locks work I have no communication with the onboard diagnostic port
JA: Are you fixing your SL yourself? What have you tried so far?
Customer: O i'm attempting to fix it myself I have a background in HVAC controller I've tested the fuses some of which have power going to them some of which is not a test of the batteries which both have power to them I've tested the main fuse box though under the right driver that's that's the passenger side
JA: Anything else you want the mechanic to know before I connect you?
Customer: There is an electrical junction device under the passenger side tire wall there's approximately six connections to that device all of them have 12 bolts to them except one has 7 V

Hi, I'm Ron and I will be helping you today.
Stand by for a moment while I prepare your answer.

First, be sure that the battery is fully charged and passes a load/specific gravity test. If this is all good, then try this reset procedure i attached for you and let me know the results so we can move on.

Please understand that I don't know your skill level or tools
you have to assist us. Also understand that I can't see, smell,
hear, or touch the vehicle either, so your patience is
appreciated. JA is a great Q/A site, but it does not replace a
repair shop. So please don’t shoot the messenger if I have to
deliver bad news:)
If you are satisfied with my answer, I would greatly
appreciate a 5 star rating now before you leave the site and I
will still assist you after you have rated me too if another
question pops up. I don’t get credit for helping you until
you rate me

Thanks, Ron

Customer: replied 1 month ago.
Thanks for the reply I assume you've read so far what I've told the other person have you seen this problem before

Nope, I only see what you posted to me. I have seen this before, so go ahead and try what I said first. let me know what happens, and make sure that new battery is good.

Thanks again and please remember to rate me 5 stars now
and keep this link in case you need me again later on.
I don’t get credit for assisting you until you rate me


Hello , Lou here , master Mercedes tech. It sounds to me like a prefuse had blown, there are two prefuse boxes for your car . I am getting you pictures now , you need to verify power coming out of all wires and if you do not then you need to either replace the fuse box or the affected fuse if it can be removed . I am getting you the pictures now . Lou

ok so here are the 3 spots that we always check after a battery replacement and a issue like yours. sometimes a big prefuse blows, there is a box in the rear near the battery and a box under the passenger side front carpet and also the round plate has fuses that allow the battery power transfer from the alternator and starter and front battery.

so you want to make sure power is transferring through that plate as well.

do not try the reset procedure above it will cause you more issues. that rarely fixes an issue.

also you have 3 normal fuse boxes, 2 in the engine bay and one in the right rear storage box where the back seat would be.

its worth it to test for power at these fuse boxes because all the power wires from the prefuse boxes are what feeds power to these smaller fuse boxes.

you will most likely find a blown fuse.

let me know if you need additional help I am the best mercedes tech you will find.

Lou .

Please take a second and click the stars at the top of the screen to rate my service so i may receive my credit , 5 stars is ideal , please request me in the future.Keep in mind that when you rate it does not end our conversation, you can still return here to me for follow up information if needed just simply reply back, thanks!
Lou P.
Master Mercedes-Benz Technician
Master ASE Certified

Looks like we had and interruption. Sorry about that. Please let me know the results of what I suggested for you to do and we can move on. I don't want to see you have to replace any unnecessary parts. My 42 years experience taught me a lot. The reset brings all values back to zero and is a great thing to try first because it causes no bad results whatsoever.

Thanks again, Ron

the ignition switch gets power from the 7.5amp fuse in the rear prefuse and also from the 80amp fuse in the front prefuse, instead of a reset lets try some actual diagnosis.

if you prefer to work with me let me know, I will be here to help you with actual mercedes diagnosis and experience.

just let me know, I will not respond anymore until i hear that you want to work with me, thanks

Lou Palomino.

Mercedes Master Tech

Customer: replied 1 month ago.
I checked both sets of fuses pre-fuses I have power or crossed all of them 11.94 V

It's obvious that Lou is guessing at this. To prove he was incorrect, you already had the battery disconnected a couple weeks ago right? This procedure just resets the complete auto electrics which in many cases fixes the whole problem.

I’ve been in the auto repair industry since 1975 and have made many improvements over
the years pertaining to proper repairs. I also share this knowledge in the classrooms I
instruct in around the country, teaching for large companies who offer high-end training
to repair shop technicians.
It all starts with listening to the customer’s complaint, confirming it and finally doing all
the needed tests to locate the problem. All these tests require thousands of dollars worth
of specialized equipment that were designed and produced for the professional
technician. So when I recommend something for you to do, though it may seem silly to
you, please trust that I’ve “been there and done that” before. Getting a baseline is critical.
Once this is done, then I confirm what I have found wrong instead of throwing parts at it,
to be sure the problem I see is NOT camouflaged by something else.
Just like when you go to the doctor’s office for a visit, they take all your vital signs such
as; blood pressure, body temperature, weight, pulse etc.
This is my approach as well, except with the cars vital signs instead. I do everything
possible to NOT leave any stones unturned because it can cause you to misdiagnose the
problem or chase your tail.
I see so many people replace everything between the bumpers to no avail and spend
money they could have saved, if they only paid for a good diagnosis.
Sad to say, I even see people offering help to someone else by just telling them what the
parts are they should replace. Ouch!! These cars are all high tech, no room for guesswork.
When the check engine light or any lights illuminate in the instrument cluster, something
is obviously wrong, and there is not a code reader on the planet that will tell you what’s
wrong, they will only give you a code that is related to the part/circuit in question. These
parts stores check codes for free, for what reason? Hmm!

Please let me know which of us you want to help you.

Thanks again, Ron

Customer: replied 1 month ago.
For your reply and I'm a little baffled that I have no power at the ignition switch but I do have power at some of the fuse points and fuse boxes the fuse box on the driver side and on the passenger side but I don't have power to other fuses I have not checked and see if I have power to the fuse box in back of the passenger seat and I at least want to be able to get the car into neutral so I could have a flatbed it to a mechanic

Towing it is no issue at all, the driver's know how to handle situations like that to get it on the bed without doing damage to anything. Rollers etc are used.

Not all power goes through the ignition switch, some is direct from the power distribution boxes under the hood.

Thanks again and please remember to rate me 5 stars now
and keep this link in case you need me again later on.
I don’t get credit for assisting you until you rate me

rpmdiag, Tech and Instructor
Category: Mercedes
Satisfied Customers: 8151
Experience: Since 1975
rpmdiag and 3 other Mercedes Specialists are ready to help you