1987 Mercedes 560SL Fuse 7 keeps blowing causing no/low acceleration
 

New informaiton: Happened again tonight and the best way to describe it is that the brakes completely lock up and then if I sit and wait long enough with the car off, it seems to clear itself.

Hello- I have a new (used) 1987 Mercedes 560SL Automatic, with 78k miles on her. The other day, I was driving down the street and she started slowing down and it became harder to accelerate altogether. I pulled over and turned the car off. After a few minutes, I started her up and put her into drive - she wouldn't move. It was as if the brakes were on. I waited about 5 more minutes and tried driving in 3rd and 2nd gears and she finally picked up again as if nothing had happened.

The guy I bought her from said that he knew the fuse blew when the fan was turned on, but I bought it anyway for a price reduction. I didn't even look to see if the fuse was blown. After the incident above, I looked and fuse 7 was shot.

It continued to drive well after that until today when I finally replaced the fuse. It drove normally for about 5 minutes and then I noticed the power coming down again just like before. By the time I got to a place where I could pull over, it would barely go. Turned the engine off and waited like last time. I noticed the fuse I had just put in was blown. This time it took several tries to get her back to moving easier. A few starts and stops, with trying it in different gears got her going a little better each time until she finally felt like something freed up and she was fine again.

One thing I did notice during all of this, at some point, is that my break pad sensor light came on for a few minutes, but I don't know if that's related or not.

Anyone have any ideas about what this could be? I know fuse 7 controls a lot of things, most of which an amateur like me sounds like it could be the cause, which gets me nowhere.

Help for a newbie, guys?

Fuse # 7 has nothing to do with your problem!

Sounds like a mechanical brake problem. Most likely a master clyinder OR booster issue.


The most common reason fuse #7 blows are the heaters on the washer nozzles. Just un-plug them.

Nice! Thanks! Now, how to troubleshoot brake issue?
 

Thanks for the information. Tomorrow I will disengage the washer heaters and see if that helps fuse #7 stop blowing.

Back to the brake issue, though... how do I begin testing for the issue? If the brake issue is most likely due to the master cylinder or booster, where do I start?

Thanks very much, by the way.

Fuse #7 still blows after disconnecting washer fluid heaters. Any other culprits?
 

]Fuse # 7 has nothing to do with your problem!

Sounds like a mechanical brake problem. Most likely a master clyinder OR booster issue.


The most common reason fuse #7 blows are the heaters on the washer nozzles. Just un-plug them.[/QUOTE]

Master Cylinder or Booster Problem
 

How should I troubleshoot whether or not this is a master cylinder or booster issue?

Fuse # 7 has nothing to do with your problem!

Sounds like a mechanical brake problem. Most likely a master clyinder OR booster issue.


The most common reason fuse #7 blows are the heaters on the washer nozzles. Just un-plug them.[/QUOTE]

You were right about the brakes
 

You were right. I needed a new booster - breaks are great now.

Fuse #7 does keep blowing, though. I took it to a place that only does wires, and they haven't been able to find it yet. I unplugged the heaters on the washer nozzles before I took it and that didn't solve the problem either.

One thing that did happen was that the guys at this place took out the master relay fuse and the fuse #7 related issues seemed to go away as far as I could tell. The fan and air seemed to be working - Does that mean the problem is not related to the blower?

Thanks for your advise!