Blown fuse?

[djbosch]

I drove my 67 230 into work today. When I turned my lights on the fuel gauge dropped to 0 and my turn signals would not work. I'm sure I've somehow blown a fuse. Before I get too far into it, has anyone else experienced this? And what was the main cause? Thanks in advance.

[Peter van Es]

https://www.sl113.org/wiki/Electrical/Fuses

Turn signals and fuel gauge are on fuse 5. Headlights are on 11 and 12 (unless if you were using high-beam). Weird that turning on headlights would cause fuse 5 to blow. You'd better investigate for shorts and or connections between 5 and 11 or 12 using a multimeter.

https://www.sl113.org/wiki/Electrical/Troubleshooting

[Pawel66]

My 2 cents (I am not a professional mechanic):
- as these two sets of electricity users are powered differently (lights directly from battery, other users on fuse 5 after ignition),
- it may not be difficult to find out if all the lights cause any fuse blown, just by turning them on without ignition.
- Similarly, without any lights on, switching on ignition, then blinkers, etc., and watching if any fuse is blown
- finally switching on lights while ignition is on would lead you to what Peter wrote

You said the fuse was blown when you switched on the headlights, but when you do it, you actually turn the switch and it goes through 2 positions of which anyone could cause the short. The fuses engaged when you turn the switch (at least for Euro) are 7,8 (position lights) then 9,10 (road lights) then 11,12 headlights (if you have them on by foot switch).

There are multiple electricity users on fuse 5 to be checked if need be. Wiring diagram would come handy.

[lpeterssen]

Dear Djbosch

As previously mentioned by my friend Pawel circuit involved in most the failed accesories you mention is fuse no.5. If you take a concentrated and thoughtful look at the pagoda wiring diagram published on this forum you will come to this findings:

1. There is a gray/violet cable responsible for the illumination feed to instrument cluster. That wire is energized as soon as you start turning your headlights switch, I mean on position 1, low driving lamps terminal 58 receives energy.  To confirm my hypothesis replace fuse no.5 ( check fuse 7 to see if it is blown also) and this time turn main light switch ONLY COUNTER CLOCKWISE to activate left or right parking lamps. (When you use parking lamps the illumination on the dashboard is not active).  If fuse no.5 does not blow this time, we are on the right track. The problem is related to cable gray/violet.

2. The cable gray/violet, meets or goes on the same path as the cable black/blue which feeds positive signal to fuel gauge at the instrument cluster.

3. Cable gray/violet as said before is the feed wire for instrument cluster lighting rheostat (dial that allows you to adjust the brightness of the instrument cluster lighting at night), and I have seen on many wiring harnesses I have refurbished before this cable making a short to ground after the rheostat.  That is because the illumination wires going to each of the individual bulbs are often not installed correctly or the cable ends get loose and touch then any metal surface around. Those are the gray/blue cables which can be seen behind instrument cluster, and also behind the heater controls.

My conclusion:

You have a MELTED gray/violet wire, because a short on any of the gray/blue wire cable ends to ground.  This melted gray/violet cable heated so much that also damaged the insulation of any of the other cables coming to the central instrument cluster fed trough the fuse no.5.  That could be a damaged black/blue fuel indicator positive lead (comes from fuse 5).

The turn signals are not working since the flasher positive feed wire black/red/green also comes from fuse no.5. So the black/blue cable insulation is damaged and is shorted to the gray/violet.  Check fuse no.7, it could have a fuse greater than 8A as should be per design and THAT WAS THE ORIGIN OF THE PROBLEM. 

An illuminated mechanic had a constantly blown fuse no.7 and decided to install one with much higher capacity.

  Ohhh my God......., thanks for these iluminatiis mechanics which give me the possibility to fix Their mess on the wire harnesses of my friends and customers.

If that fuse is not blowed, you have also damage on the cables going to the low driving lamps (terminal 58) cables grey/red And gray black.

You have a lot of work to do to resolve this issue. The damage is in the main wiring harness in the section between main fuse box%u201412 pin connector for the instrument cluster.  And from that point, also the cable going to instrument cluster is damaged.

First, main wiring harness has to be taken out.  Then all insulation /protective tape, or velour has to be removed.  You have to trace each cable and look for signs of melting.  Start with cables close to 12 pin connector. 

If you need further advise, write me a PM. OR ..... If you need an already refurbished wiring harness for 230SL, I have some for sale.

Best regards
L.peterssen

[ejboyd5]

Did you actually "blow" a fuse or is it merely a poor connection occasioned by corrosion?  Clean the contacts and try again. If blown, replace fuse No.5 and try again.  It may have been a coincidence and No. 5 simply failed from age. Don't knock yourself out with involved diagnostics unless you can replicate the problem.

[ja17]

Good advice from "ejboyd5 ", check for a corroded fuse which has lost contact. I like to use the fuses with the brass metal since they do not corrode as bad as the ones with the aluminum metal.

[lpeterssen]

Dear ja17:

Double check that, since my instinct says there is a melted wire somewhere. Clean fuse holder contacts with a fine grit sanding paper as no.180 as suggested by ejboy15 and also make sure that all fuses are of the right rated amperage.  It is 8A for each of them except fuses no.2 and 6 which are rated 25A. 

Repeat the chain of events that brought you last time to the blown fuse and see what happens.

Remember, first turn main light switch COUNTER CLOCKWISE to confirm that parking lights activated does not blow the fuse.  Then turn ignition to ACC position and turn lights one step by step. Position lamps first and then Driving lamps.

Regards
Leonardo Peterssen