Starter doesn't turn over...

[ciocchettim]

Hello all,

I'm new to this site and a 1970 280SL (although I've had a 64 230 and 68 280).  I picked up this car from an older gentlemen who started an amatuer resto back in 2000 and hurt his back and as the story goes the car sat until my dad and I pulled it out of his garage in pieces last weekend...

We trying to get it to start but the starter doesn't engage.  I've searched the forums but nothing addresses my issue exactly.  When I turn the key there is power at the fuel pump (disconnected the pump to keep the old gas from the injection pump) and the bottom (of the two) 10mm nut on the solenoid although the test light is very dim.  There is always power on the 13mm nut on the solenoid and the solenoid ground wire is good.  When I turn the key, nothing happens except for a click in the relay (pic attached).  If I do a jumper from the 13mm to the 10mm nut, the motor turns and the car fires right up (amazing after 9 years of sitting).

Based on all of this, I assume:

-the battery and connections are ok since I'm using power at the starter to turn it with the jumper

-the ignition is ok b/c it bringing power to the fuel pump and solenoid (although it it weak there)

-the starter is ok

-the clicking relay is ok (I swapped it with one from our running 66 250 coupe)

Thoughts?

Thanks!

Mike
01 M3 Cabrio; 86 280GE Cabrio; 73 280SEL 4.5; 70 280SL; 66 250 SE-C

[scoot]

Let me guess.  Your car is an automatic.  There is a cable going from the transmission to a switch unit that is on the firewall of the car under the hood.  That switch unit tells the car if it is in Neutral or Park, and if it is, then it lets the car start.  Perhaps either the cable is out of adjustment or more likely, there is slop in the transmission linkage and the switch on the firewall doesn't think you are in park or neutral.    I would try carefully to start the car with the transmission selector in each of the other positions and see if you get it to crank.  If you do then my theory is supported.   If you don't have automatic transmission than ignore all of this.

[ciocchettim]

Thanks for your response.  It is an auto.  I saw the posts on here so tried the switch on the firewall in each position with no luck...we're stumped 

[scoot]

Thanks for your response.  It is an auto.  I saw the posts on here so tried the switch on the firewall in each position with no luck...we're stumped 

Hmmm.  I think that there is another relay but I'm not sure which one it is (or even if I'm right), or it could be the ignition switch itself isn't working or isn't connected for the "start" position...

[Cees Klumper]

Could just be that the starter itself is 'asleep' - although it sounds wacky, give it a blow with a hammer and see if it helps.

[su8pack1]

I'm having the exact same problem on my automatic 69 280SL. I replaced the battery and had the starter and solenoid rebuilt. The only thing I get when I turn the key is a click from the top solenoid on the back of the injectors. Still working on it.

[su8pack1]

An update. I've installed a new battery, had the starter rebuilt, replaced a starter relay and the starter switch. Automatic neutral switch seams ok as when put in reverse the backup lights come on. Have patience if you do the starter switch, 2 to 3 hours if you're lucky. Still no start, just the injector solenoid click and fuel pump hum and no power in the wire from dash starter switch to starter. Today I bought a push button switch from Advance Auto for $5 and ran it from the battery to the same post on the starter as the one from the dash ignition switch. Turned the key and let it spring back still without starting. I then pressed the new starter switch button, and bingo it started. When I turn the dash switch off it shuts down as usual. I still have to figure out why I'm not getting power from the dash switch to the starter. But at least I got it started. I think I'll replace the key tumblers next.

[66andBlue]

No need to mess with the tumbler - check the switch first.
See this info in the technical manual: http://www.sl113.org/wiki/Electrical/IgnitionSwitch
Good luck!

[su8pack1]

No need to mess with the tumbler - check the switch first.
See this info in the technical manual: http://www.sl113.org/wiki/Electrical/IgnitionSwitch
Good luck!

Thanks, but I have already installed a new starter switch purchased from the local MB dealer. I guess there is the possibility that this switch is bad. Getting out those 3 screws was a nightmare, working with a mirror and angled screw driver. The 280SL switch is different than the 230SL switch in the article on the output connection side.

[Allenh]

The first thing you MUST do is dispose of the test light.  Get a Volt-ohm meter.  The first step in troubleshooting is to KNOW what the voltage is at the device or load you are investigating..  Too many techs in my shop didn't have an accurate clue at to what theywere doing-  I would fire anyone who used a test light!

With a volt meter, test the solenoid wire on the starter with the key switch in the start position.  Pickup the B-, ground, at the starter mounting bolt.  you should have 12.6 volts.  Anything less than 12 volts indicate a circuit problem.  If you have 12 volts, the solenoid is bad.  Since you are able to crank it by jumping 12 volts from the battery terminal of the starter, it is easy to assume the problem is in the circuit.  An easy way to test the ignition switch is to see if you have 12 volts when cranking on the Thermo switch by the temperature guage at the left side of the engine. 

Troubleshooting electrical problems need the use of a V-O meter, electrical schematic and discipline.  Always test your meter by reading battery voltage, somewhere, like the battery, to be sure it is working and tht you do have power for the circuits.  Do all you testing with applied voltage, Use the ohm scale for bench testing.

If you get this far and still have an issue, let us know how far you have gotten so further guidance can be given.

Earlier posts ask if yu have an automatic transmission.  Use your schematic to follow the circuit path from the key switch to the starter relay.  You will find the problem.

I would say good luck but luck has nothing to do with it.

Allen

[su8pack1]

As a backyard mechanic for more years than I care to remember the test light has worked for me, but I know what you mean. I'll have to get a V-O meter for this one. Yes it is an automatic and as I said earlier it appears to be working as the backup lights come on only in reverse. Thanks

[hands_aus]

the contacts for the starting circuit are different to the contacts for the reversing lights.
You should think about testing for continuity the neutral safety switch with the plug removed.

[su8pack1]

the contacts for the starting circuit are different to the contacts for the reversing lights.
You should think about testing for continuity the neutral safety switch with the plug removed.

I just meant the automatic neutral switch was in the right positions for the reverse lights to come on.