Ignition switch problem to be confirmed ?

[VincentR]

Hi All,
Last week end I had a drive with my 280sl 1970.No starting problem.
Then I stopped (switched off the ignition) in my downtown underground garage (which is not my home place) to open my garage door. Then when I wanted to restart, the car in a first time run but only around 3 seconds. It seems that it stopped when I switched on the headlights (but I'm not sure, maybe no relation with this).

Then I tried again to turn on the ignition switch, but no result. So I parked the car in the garage by pushing it by hand. And I disconnected the battery.

I came back yesterday in the garage. I made the following procedures :

a) headlight switch was still on (I forgot it the last time) : I plugged the battery and opened the car door to check if there was current on internal light : no light. Then I turned on the key on position 2 (position before position 3 which is starter) and fuel pump was not running...

b) In order to be sure of the battery, I disconnected it, then I turned off the switch light to 0 (I susopected one short circuit of light switch). Then I plugged back the battery. I then opened the door : result = internal light was lighting. Then I turned the key to position 2 and the fuel pump was running. I tried key position 3 and all was out.
NOTA : I did not make this procedure again without key position 3 in order to check if the light and fuel pump were still on in position 2.

I checked the electric diagram and I have seen that there is no starter relay. Starter is feeded directly by ignition key switch (if I did not make mistake).
So my conclusions are :
a) either faulty power battery (not sure because fuel pump was running).
b) either faulty ignition switch electrical device (the plastic/metal cylinder end on steering colum ignition switch) : I would suspect it.
c) either faulty starter solenoid.

QUESTION :
Can I start the car by putting ignition key on position 2 and then feeding directly the starter solenoid with the battery + terminal (through one remote ignition switch comong from the battery + terminal) ?
It seems by checking the electric diagram that the cold start fuel system is electrically feeded  in key position 2 (so I won't have cold starting problem).
(the target is to drive out the garage to come back home and to then fix the problem of the ignition switch...I have more place to work at home...).

Thank you in advance for your feed-backs.

Vincent R
Besançon - France.
280sl 1970

[450sl]

Hi Vincent, if your car has an automatic gearbox my guess is that the switches connected to your gearselector are prohibiting starting .
mark

[mrfatboy]

This old thread from 2012 should/might help you out.

https://www.sl113.org/forums/index.php?topic=16067.0

[lpeterssen]

Dear Vincent

Yes you can feed directly the T50 of your starter selenoid with positive from battery through a remote starter switch.

Your cold start mechanism will still operate since it will be back fed trough the T50 wire which goes to the parking/neutral safety switch were those relays take the signal to activate it.

Check battery condition with a battery tester. They are cheap and useful every time.

I think battery is weak. Since there is no correlation between starting  and headlight switch unless the power available is so weak that the headlight consumption killed the battery.

Regards
L.peterssen

[VincentR]

Hai All,

Thank you for your answers.
One information : my car is with manual transmission.
As per advised by L Petersen, I will test the battery but I when I started on the morning (before the problem occured) the battery was strong.
I will come back to you asap.

Best regards.
Vincent R
Besançon - France
280 sl 1970 Manual Transmission

[450sl]

+ 12V  on your starterterminal number 50  (thin violetwire) will do the trick ; if not , tapping on your startermotor might do.

[Cees Klumper]

Vincent - from reading your symptoms, it could be that one of the main battery cables (earth or plus) is loose somewhere. Either on the connection to the battery terminal, at the engine block (negative/earth) or the plus (I think it goes straight to the starter). Poor or corroded connections of these main cables can also cause your issues, I believe.
If the ignition switch is the issue, I found a relatively inexpensive one last year in the UK, and had it shipped to me in France. SOme work to install but not too bad. In the meantime, as others have said, running a small wire from the plus, or that (I think temperature sender terminal) to the starter solenoid will also do the trick, if the ignition switch still works on setting 2 (but not on 3 to start the engine).
Bon chance!

[lpeterssen]

......In the meantime, as others have said, running a small wire from the plus, or that (I think temperature sender terminal) to the starter solenoid will also do the trick, if the ignition switch still works on setting 2 (but not on 3 to start the engine).
Bon chance!

Please do not do this as the gauge of the Rose/blue cable at the TTS (temperature/tie/switch) is too thin only 0.75 mm2.  T50 cable going from ignition switch to starter selenoid is 2.5 mm2 in section (awg14). So if you do what suggested by friend Klumper you will melt that cable as I have seen on many refurbished wiring harnesses that came to my hands.

Bets regards
L.peterssen

[stickandrudderman]

The first thing to try is another power source; easiest done with jump leads.
If with another power source your problems are resolved then you either have a battery or an alternator problem.
It sound so me like the charging system was not working on your drive to your parking and you exhausted the battery voltage.

[Cees Klumper]

Sorry LPeterssen, but this is how I started my Pagoda for several years, before I finally replaced the ignition switch. The current went not through the wiring harness but through my extra-wire I ran from the plus to the starter solenoid.

[lpeterssen]

Sorry LPeterssen, but this is how I started my Pagoda for several years, before I finally replaced the ignition switch. The current went not through the wiring harness but through my extra-wire I ran from the plus to the starter solenoid.

No problem Cees.  I know many people does that, but at the end T50 signaling cable going to TTS (rose blue) which passes trough all the cold start mechanism port 85 relays get’s cooked (melted).  And any melted wire is a source of electrical problems.

Regards
L.peterssen

[VincentR]

Hi All,

To L Petersen : I think you mixed the post from Cees and the-one from 450SL. 450SL suggested to plug on T50 terminal. Cees did not suggest that. (this is just to clarify).

As you suggested me, I ordered one battery diagnosctic tool (with power analysis option). As soon as I receive it I will use it.

If the battery is OK, I will control the leads (especially the-one going to the starter) as suggested by Stick/Colinfern.

I will keep you informed asap.
Thank you again to all of you for your support.


Best regards.
Vincent R
280sl 1970
Besançon / France