Mystery: Turn key, nothing, what’s wrong?

[AdelaidePagoda]

Electrical expert, I need your help in diagnosing and treating this ailment.

After a weeks holiday I went to start my daily driver 1964 230SL. Turned the key and nothing. Absolutely nothing. No ignition lights, no fuel pump noise, no ignition, no headlights, nothing. Thinking it was a flat battery (brand new, only three months old) I called the local road service.
 
They arrived and confirmed it was not the battery (12.6V). He tested all the usual electricals and found power to the starter motor and alternator, although only fuse 1 in the fuse box. He suspected it was the ignition switch or the starter relay and suggested it gets towed to its usual Mercedes mechanic.

If this happened to your Pagoda, where you are your next steps?

Closest diagnostic answer or the best solution to get it back on the road, wins!

[BobH]

Hello Dave, if you hadn't said the headlights were not working, then i would have suspected a bad ignition switch

The fact that your headlights are not working either, which are not controlled by the ignition switch, then possibly a bad main earth.  Check the battery connections, they may look ok, but remove them, clean and tighten, including the other end of the battery ground strap, again remove clean and refit

Your mechanic may have measured voltage at the starter, but a bad connection would prevent current being drawn

The problem may seem drastic, but will probably have a simple fix

[AdelaidePagoda]

BobH, you fill me with optimism!

The mechanics did take off both battery terminals and cleaned them. As mentioned it is a new battery so those terminals are very clean.
He did not check the battery ground strap, so that is my next job!
One other curious point I forgot to mention, but you just reminded me. Whilst he was under the dash trying to access the ignition switch (not successfully) the headlights suddenly flashed on for a second and then went out. He could not replicate this, but it confirmed the battery was working. Not sure if this helps the diagnosis?
Thanks all for considering this issue.

[Paul & Dolly]

I seem to remember that everything feeds from the lighting switch, so  I would check for some discontinuity there.

Are you getting  any power to the lighting fuses in the fuse box ?

Good luck
Paul

[Jack the Knife]

BobH, you fill me with optimism!

The mechanics did take off both battery terminals and cleaned them. As mentioned it is a new battery so those terminals are very clean.
He did not check the battery ground strap, so that is my next job!
One other curious point I forgot to mention, but you just reminded me. Whilst he was under the dash trying to access the ignition switch (not successfully) the headlights suddenly flashed on for a second and then went out. He could not replicate this, but it confirmed the battery was working. Not sure if this helps the diagnosis?
Thanks all for considering this issue.

I just removed my ingition two days ago along with my wiring harness.

I am not mechanic so there could be alternate methods, but I believe you will need to remove the speedo and tach if you actually want to put your hands on the ignition. Of course, you could send a camera in there much more easily.

[Raymond]

I'm with BobH.  The most likely culprit is an open ground somewhere.  The light flash might indicate a short but that would cause other issues.  Did you try jumpering the starter solenoid to see if it spins?

[Paul & Dolly]

If you look at the wiring diagram, item 36 is the rotary light switch  and item 37 is the ignition switch.
Terminal 30 on both is the B+ feed from the Generator 43, starter motor 41 and battery 40
If that link is malfunctioning you will not get any lights or starting.

Good luck

Paul

[BobH]

Whilst he was under the dash trying to access the ignition switch (not successfully) the headlights suddenly flashed on for a second and then went out. He could not replicate this, but it confirmed the battery was working. Not sure if this helps the diagnosis?
Thanks all for considering this issue.

Ah, so the headlights might be working, albeit very iffy

Do they stay on when you turn the headlight switch on?  if so it could still be a bad main earth, but i'm less convinced now.  As Paul says, the +ve feed to the lights and ignition switch meet and greet at terminal 30 on the light switch, if these terminal connections are loose you would lose the feed to the ignition switch and the starter, and of course if the headlights work, but no ignition it could also be a bad ignition switch. 

Let's hope it's just a bad connection somewhere!

[lpeterssen]

Dear Dave

Need more details to give you an expert guidance….

Leonardo Peterssen
Www.wiredoktor.com

[lpeterssen]

This is how it works……

With the clues given on first post we may conclude…

1. Power on circuit 1, but not on any other circuit.

 Circuit one is fed directly from main light switch.   That means that power to main light switch is being received.   The fact that power could be measured at that point also means that battery ground connection to chassis is correct.

2. No main lights.  Makes no sense since you confirmed that circuit 1 has power, therefore lights should come on and be lid.   Each headlight has its own grounding post.

3. No power on any circuit except no.1, means that UNDOUBTEDLY the IGNITION SWITCH is defective, or the RED/black 2.5 mm line between IGNITION SWITCH and input side of main fuse panel for circuits 2 through 6 is compromised, loose, etc.


I think that you should clean and sand all those terminals and if that doesn’t work you need to service your harness by someone who knows better……

Send your harness to a SPA an forget about all those gremlins.

Best regards
Leonardo Peterssen
Www.wiredoktor.com

[AdelaidePagoda]

Leonardo,

Thank you for sharing your expertise. First thing this morning, I did recheck all the battery terminals and the ground strap, which whilst slightly corroded at the fender panel, did not alter the outcome.

Key turn, still nothing. No dash lights, no sounds from the engine bay or fuel pump. Just a click of the key turning.
To your point, still no headlights!

One interesting new finding is that the underdash light does work, when the switch is turned on (normally left in the off position).

Any advice that you can provide on the exact location of the terminals that require sanding would be appreciated. Is that under the dash at the point of the ignition switch or under the hood, behind the fuse box?

Many thanks, David

[lpeterssen]

David

Start doing the following.

1. Main light switch is the power hub on a w113.  Remove battery ground first.  Then remove main light switch knob with a strong pull outwards and aftr that remove the chrome nut that holds it to the dashboard.  Push light switch in so that it falls down.

2. Check all terminals in that main light switch.  Remove one by one all terminals, and brush the terminals and the contacts at the main light switch.  Do one at a time.

3. Remove the tachometer, to gain access to your ignition terminals.  I do not remember if your car was 230 or 280.  If it is a 280, the work is easy just unplug the round connector to ignition switch.   Find sand paper grit 240.  Make mini rolls that fit into the round terminals, sand each of them until shiny.  If your car is a 230sl or 250, instead of just pulling the round connector, you have to remove 3 flat screws that hold the tumbler switch attached to ignition lock mechanism.  Once removed you will have access to the ignition tumbler switch.   Remove each terminal and sand them.  Same thing to ignition switch.   Do one at a time.


4. As the tacho is removed, you have access to main grounding post behind the dashboard.  Remove the 10 mm nut that holds it them in place.  Sand surface where it grounds and also the 0 shaped terminals.

5. Sand and polish your main grounding post at the battery.

6. Try again reinstalling everything back.   

7. Remove main fuse box, by loosing the screws that fix it to firewall. Push it to cabin.   Lay down inside the cabin, and pay attention to a RED/black cable that is attached to circuit 2 input side.  It is together with a smaller gauge also red/black and a blue/red cable.  Remove those.  Sand the terminals and also the port on the fuse box to assure perfect connection.   That cable feeds all T15 circuits 2 through 6.

8. If circuits 2 through 6 are still with no power change the tumbler switch.

After that report to see.

Best regards
L.Peterssen
Www.wiredoktor.com

[Charles 230SL]

Dave, seems you replaced your 35a alternator a couple of years ago. I'd take a look at the 10ga wire that runs between the starter and the B+ terminal on the back of your alternator. That wire gets hot from current and from heat off the exhaust manifold, and after 61+ years it may be burned and brittle. Several members of this Group (including me) had to replace that particular wire because it was damaged from heat. If the wire was brittle, when you replaced the alternator you may have disturbed it enough to break some of the strands causing additional resistance and heat. Another 10ga wire runs from the alternator B+ terminal to the light switch which as Leonardo pointed out, is the power hub on a W113. Check condition of this 10ga wire too, particularly around the ring terminal. These wires can be visually inspected but you'll need to get under the car.
https://www.sl113.org/forums/index.php?topic=27245.msg196606#msg196606

[AdelaidePagoda]

Charles,
Thank you this is a very thoughtful and experienced suggestion. I did have a quick visual check and it seems they are both intact, although I have plans for a more detailed investigation in due course.
All suggestions are welcome, getting these cars back on the road takes the whole village!
Dave