Right side turn signal short diagnosis help

[TDw113]

Hello,

I'm new to this forum. I searched for previous messages on this topic but couldn't find any matches. Please forgive me if this topic has already been discussed and point me to the relevant discussion.

I have a 1966 W113 230SL that recently had its turn-signal relay burn out. Following a thread on this forum, I ordered a modern replacement part. After replacing the relay, the left turn signal functions correctly, but when indicating right, the relay burns almost immediately. Upon inspecting the front and rear bulbs, I found the rear one was broken. I replaced it with a new bulb, but now not only does the relay blow, but also the fuse (16A fuse!).

I assume there is a short somewhere in the wiring, possibly caused initially by the broken bulb, but I was wondering if someone could point me to the more obvious locations where the system could have developed a short. I ordered a workshop manual to get a better look at the system as a whole, but it takes its time shipping, and the annual inspection is rapidly approaching, so I need to get this sorted.

Any advice would be appreciated!

Thanks,
Tom

[lpeterssen]

Dear Tom

My name is Leonardo Peterssen and I run a personal hobby business called www.wiredoktor.com. Also have been writing here, on the electrical forum section,  for long time helping other Mercedes Benz owners, as is the case right now.

I will suggest first to become a full member so that you can access the Technical forum section and also all the manuals and diagrams published there.

First of all, all fuses in your loved Pagoda should be rated 8A, except fuse no. 6, which should be of 25A.

The fuses should be of that value so that when a short comes they act immediately and no other electrical accessory gets burned as is happening to you.

When you install larger fuses, if there is a short, the cable itself that has a short somewhere will start to melt and then, the damage will be more extended.

You have to proceed systematically to find out where the short is.  You have a clue that it may be on the rear part of your W113.

Let’s start:

1. Unplug rear harness from main harness. 
There is a large 12 pin male connector on the LEFT SIDE FENDER footwell inside the cabin.  That connector is behind the  hood latch handle.

2. Replace again fuse no.5 (8A) and install a new blinker flasher. 
Repeat testing procedure just with ignition switch on the RUN POSITION without cranking engine.  By the way, with rear wiring harness disconnected your fuel pump will not receive energy and therefore the car will not run for long.

If when repeating the test the fuse no.5 did not blow, then we are 100% sure that problem is on the rear harness.

If that is the case the best approach will be to replace the REAR HARNESS which is not so expensive, in the range of 700$ plus shipping.

If you want to repair yours, best practice is to remove it from the car and work on a bench.

Remove all PVC tubbing and replace any melted lines or cables with compromised insulation.

The power cable that feeds the right side turn signal is BLACK/green. Do not attempt to do a parcial cable substitution or splice since it will work only for a while.  Those cables are exposed to very damp conditions so any splice will fail in short time.  It’s better to run a completely new line from 12 pin connector to the 6 pin connector that feeds the right tail light assembly.  At same time replace your fuel pump feed wire which is the thick black wire with external cotton insulation, since that gets often compromised as well.  Do also a replacement of ALL GROUND lines. They are vital for a happy electrical system.

Your BLACK/green cable should have now extensive damage since a 16A fuse has been installed for some time.  So no partial repairs please.

Best regards
Eng.Leonardo Peterssen
Www.wiredoktor.com

[TDw113]

Dear Leonard,

Thank you for the detailed post. I will follow your suggestion to diagnose the fault. At this point, I hope it's just a wiring issue.

Another thank you is owed for the information about the fuse rating. The 16A fuse was installed by the previous owner of the car, and we never thought to check if the fuses were the correct rating as the car was functioning for some time as-is. I assume there was a reason they placed a 16A fuse. Obviously, they should have diagnosed the cause of the high current draw instead of mending it with a bigger fuse.

I will report back with the findings!

Thanks again,
Tom

 

[Sead]

Dear Leonard,

Thank you for the detailed post. I will follow your suggestion to diagnose the fault. At this point, I hope it's just a wiring issue.

Another thank you is owed for the information about the fuse rating. The 16A fuse was installed by the previous owner of the car, and we never thought to check if the fuses were the correct rating as the car was functioning for some time as-is. I assume there was a reason they placed a 16A fuse. Obviously, they should have diagnosed the cause of the high current draw instead of mending it with a bigger fuse.

I will report back with the findings!

Thanks again,
Tom

I would inspect turn signal switch first. Taking it out of car is a few min job...

[lpeterssen]

Dear Sead

Good suggestion.

Best regards
LP

[TDw113]

Thank you, everyone, for the suggestions.

I finally had some time to work on the car.

I examined the indicator switch and found nothing. I followed Leonard's protocol and, indeed, the rear harness is causing a short. I dug up the harness and found some questionable modifications made by the previous owner of the car, so I will be replacing the harness.

Leonard, I can't find a rear harness on your website. Can you share a link?

Thanks,
Tom