Electrical Systems

[Sphe]

If you don't remember me, I'm Eugene the kid restoring the 230 with his dad last summer. Well we're back and working on it again! And along with restoring the gas tank, we're trying to turn over the engine electrically. Here's our first problem:

So we connect the car to a battery, and the lights come on. We turn the key to 2, and the inside lights come on, the air blower starts working, and the car horn works. Turning the key to turn over the engine, I hear a loud pop from under the hood, and everything shuts off, and wont turn on again. The fuses are not blown, we've checked them. This happened at the end of last summer, but we were closing up shop and haven't touched it since. So apparently after a year, the car fixed itself. But we did it again, and I'm not waiting a year to do it again. What could be going wrong? Am I forgetting something here?

[mdsalemi]

Sounds like something with the solenoid?  Since you are in the process of restoring or repairing the car, why don't you take the starter out, and take it to an auto electric shop.  They will usually test it for free.

Beware: there are "off-brand" solenoids that can cause problems.  I had a local shop rebuild by starter, and while it bench tested OK, repeatedly might I add, "in car" was different.  The solenoid would NOT disengage the starter and it kept turning.

Upon further inspection, the solenoid was NOT a Bosch; we replaced it with the OEM and then all was well.


Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

[Sphe]

sounds ok.... but why would the starter prevent the rest of the car from working?

[Benz Dr.]

A click is the solenoid but a pop sounds like a loose wire that's jumping current. Check all your conections and clean the wires going to the starter. Having it rebuilt sounds like a good idea if you take it out.

Dan Caron
 SL Barn

[Sphe]

I figured that it might be some sort of capacitor somewhere, which is why the same thing happened last year, and a year later i was able to turn it on again... maybe the year gave the capacitor a chance to discharge. At least that's what i thought.

[pkiefert]

use a voltmeter to try to find where the battery power stops. As Dan indicates, most likely a bad connection somewhere, probably a high current one. Or at least have an assistant watch the engine compartment to narrow down where a sound or arcing is happening. But be advised electrical arcing is not a good thing in the engine area so that would be a last resort thing. Keep a fire extinguisher handy.  Non-destructive diagnosing is highly recommended.

[hands_aus]

Hi Sphe,
In the Ignition circuit there is supposed to be a Time Relay which won't activate again until the ignition switch has been returned to OFF.
Could it be shorting to earth?
I am not sure if it shuts off the whole electrical system though.

Bob (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[Sphe]

How do I return the switch to off? And how do i get to it? I don't know where it is.

[Benz Dr.]

He means the ignition switch. You have to turn it to the off position every time you restart the car.

 You can have most things working in the car and the starter won't work at all.
 The power goes from the battery to the starter and then to the headlight switch. From there it goes to the ignition switch and a small wire runs from the ignition switch to the starter solenoid.


Daniel G Caron

[Sphe]

so if the headlights should work, even if the starter is completely shot... what could prevent them lighting?

[ja17]

Hello Sphe,

Sounds like you have a bad battery connection. Economy replacement battery cable ends are notorious for this kind of problem. Remove any clamp on ends and clean them or replace the whole cable.

Joe Alexander
Blacklick, Ohio

[Sphe]

So according to benz dr. the headlights should be the first thing that should be able to work, regardless of whether or not the starter is shot... but what i'm wondering, if there is a break in the current across the starter, will the headlights still work?

Sorry for being stubborn, It just confuses me that it works at first, then once the starter is used the current breaks somewhere. Then, after waiting a long time, It works again.

I admit i haven't tried reconnecting it again, due to the fact I got a job, so i haven't had much time at home to work on the car. But I will try it soon.

To troubleshoot... If I bridge the connection across the starter, will the headlights work, or will i blow a fuse?

[George Davis]

Sphe,

the headlights (and other electrical stuff) are not connected ACROSS the starter, but they are all connected together AT the starter, where the battery cable connects to the starter.

What happened is that you had a loose or poor connection somewhere.  Electric current was able to flow across it to power the lights and other stuff.  But when you tried to start, the starter draws a huge amount of current, and this huge amount of current arced at the loose/poor connection (that was the pop) and at the same time burned the connection so current will no longer flow across it.  That's why nothing works now.  As several have already said, you have a bad connection somewhere.  That is the basic problem.

Your starter and/or solenoid may be bad or good, but you won't know until you find the bad connection and clean it and connect it properly.  There are no capacitors involved.

Connections to check, clean, wirebrush until they shine, and tighten are: battery connections; connections from battery clamps to battery cables if replacement clamps are on it; the connection where the battery cable connects to the starter; and every ground you can find.  There should be a heavy ground cable at the rear of the block to the chassis, as well as chassis to battery.

Good luck!

George Davis
'69 280 SL Euro manual