Riddle Me this

[Harry]

1966 230SL

I posted and several of you replied recently regarding issues I was having with my ignition after installing a 123 Distributor.  The issue was that the ignition was still getting power even with the key removed, i.e. the fuel gage worked, the generator light was on - just as though the ignition switch was in the Run position.

The way this was remedied was to undo something that I had done as part of the 123 installation.  I had discreetly placed a jumper wire across the ballast resistor and otherwise left the other wiring to the resistor intact.  For some reason, I elected to remove this jumper and the problem hasn't resurfaced since.

Honestly, I'm not quite sure why.  The ballast has three wires attached to the "input" side.
- One from a larger cable bundle that runs along the front frame rail
- One from the relay (cold start I believe), and
- The one that goes from the ballast to the coil

This could just be coincidence and the problem is intermittent, working correctly for time being.  The initial problem had persisted even with all of the fuses removed, so I expected that the power source had to be coming from the relay (which has direct power from the starter).

It's worked fine since I removed the jumper but it's not clear to me why/how that could have been the root of the problem.

Thoughts?

Thanks,
Harry

[Cees Klumper]

On my car the ballast resistor only has/had two wires, one on each terminal. Are you sure your setup conforms with the applicable wiring diagram?

[BobH]

Hello, there were two methods of bypassing the ballast, either with a relay, not sure where this would be located, or by upgrading the starter, with a later starter that has a +ve bypass connection going directly to the ballast.  Either method bypasses the ballast, but only when the ignition is on or the engine is cranking.  I'm not clear when you say you connected a jumper wire across the ballast, is there literally a wire shorting out the ballast?  if so then maybe there would be a route for a +ve backfeed

Have a look on here for the correct two methods

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

[Pawel66]

The wiring you have is wrong, someone hooked something to power supply after ignition in a wrong way.

As Cees states, in-series resistor has to wires: one from fuse NO.2 and one to coil. These 2 you just connect together when omitting the resistor.

It looks like the wire from the harness is the one from fuse 2 (pls check it) and this one should stay.

The other one, from cold start potentially, I think you need to check what it is and wire it as per the diagram. Pls check if it is powered with ignition off - it can be anything...

[Harry]

All very interesting.  My understanding of the power to the coil based on the Tech Manual is that during starting, the coil gets full battery power.  Once started the coil is fed through the ballast, providing reduced voltage.  Based on what I see on this car, the relay is fed 12v directly from the starter ("1" in my diagram).  I had assumed that during starting, the battery voltage was provided through the relay directly to the coil ("2" in my diagram).  Once started I had assumed that the wire from the frame bundle ("5" in my diagram) or the wire from the relay ("3" in my diagram) provided power to the ballast.  This reduced run voltage was fed from the outlet side of the ballast to the coil ("4" in my diagram).

RECALL: In the photo I have the outlet side of the ballast connected to the input side of the ballast.

When the ignition switch is in the run position, the wire from the bundle shows 12v, while the wire from the relay shows 0v.  But the "3" wire from the relay also shows 0v during the start cycle?  So what is the purpose of this wire from the relay to the ballast?

I never understood the apparent duplicity of wires "5" and "3"?  It would be nice to know what this relay is actually for on this car.

Thanks again for the help,
harry

[BobH]

From what i can deduce, this looks correct for the relay to bypass the ballast

Wire 1 feeds the coil of the relay, only when cranking, relay energises
Wire 5 from ignition switch feeds +ve to one side of the ballast, during running, ie not cranking, then the ballast is in circuit, and feed the ignition coil on wire 4
Wire 3 connects this same +ve feed to one side of the relay contact, when the relay is energised, (only when cranking) this connects the +ve to the ignition coil on wire 2, thus bypassing the ballast

Did you say you added a jumper wire as well, where was this connected?

[Pawel66]

I think the jumper was added between connectors on the ballast resistor.

Yes, I think the arrangement (not original unless it was used in 230SL) works for bypassing the ballast resistor during start up to help spark, however it makes sense only if +12V from starter is coming from connector 50 and powers up relay only when cranking.

To answer directly:
wire 5 provides +12V when ignition is on
wire 3 takes this +12V and through relay gives it to coil bypassing the ballast, so it is more ballast to relay, not relay to ballast wire

Wire 3 is delivers +12V to relay all the time when ignition is on. And this voltage goes further to coil only when cranking (relay activated by wire 1).

I would check if wire 1 is connected to connector 50 or 30 on your starter - does it have power all the time or only when cranking? If it is connected to 30 on starter, you will have your car powered up without ignition key all the time.

You may also mark relay pins on your drawing.

Anyway, to the best of my knowledgde, the factory arrangement does not have this relay. At least for 280SL. It goes: fuse 2 - ballast resistor - coil.

[Harry]

Aaah.

BobH - your explanaton seems to agree with the physical wiring.  So the relay is a starting relay used every time the car is started.  I had incorrectly assumed that the wire from the starter to the relay was 12v all the time, but it is not.  It apparently is as you and Pawel66 say "+12V from starter is coming from connector 50 and powers up relay only when cranking".

The jumper wire was simply across the terminals of the ballast.  I moved it to the "input" side of the resistor, completely bypassing the resistor, seemingly making the original problem go away.  Only now I don't see how that could have made any difference.  That problem had to have been in the ignition switch - which I replaced.

Agreed?

Very helpful!!!
Harry

[BobH]

If you only shorted out the ballast with a jumper, then all you did was replicate what was already there, albeit it it would be shorted at all times.  You didn't introduce another +12 V supply, so couldn't feed anything back to the switch and fuses.  So, yes the original problem would appear to have been with your ignition switch

I understood you no longer need the ballast in circuit with 123 ignition? so is there a need for the bypass relay?, just move the wire and take the ballast out of circuit

[Harry]

BobH,

No - there's really no need for the ballast other than to provide a common post for the other wires (already fitted with a connector) to be tied together.  The resistor itself is essentially of no other value, other than being there for cosmetic purposes.

Thank you all again!  I always enjoy learning a little more about these cars.

Harry

[Pawel66]

As BobH says, you do not need that relay either, it makes no sense if resistor is not there.

[Harry]

Hmm.  That's true.  I guess I could just disconnect the wires from the ballast and coil them up but I would still have the 12v feed from the starter.  I guess I could do the same for it, just a longer coil.  I have to agree there's no point in continuing to power the relay.

Thanks very much,
Harry

[Pawel66]

Disconnect wire 1 from starter.
Disconnect wires 3 and 5 from ballast.
Disconnect wire 2 from coil.
Disconnect ground from body.

Unscrew relay, put it in the drawer (you have a nice relay with rubber mounts - valuable items). Paint the edges of the holes after relay screws with something.

Disconnect wire 4 from ballast.

Unscrew ballast, put it in the drawer.

Connect wires 5 from harness and wire 4 from coil, insulate the connection.

[Harry]

Thanks again Pawel!