hey all-
my euro 250 whose motor recently got a 2nd lease on life is still having ignition problems. it appears she has the exact same ignition setup as my (also inoperable) 280e: (2) starter pre-resistors and a transistorized ignition.

she seems to be getting intermittent voltage at the resistors. she'll show no power there, but a couple times when i accidentally left the key in the "on" position, i noticed the resistors heating up, realized she's somehow gotten power, and she's started up. however, this solution doesn't always work...leaving the key 'on' doesn't necessarily get her the voltage flowing, and flipping the key back and forth doesn't seem to work either.

even when i just 'hotwired' one of the resistors (the red wire on the 4 ohm one) she doesn't seem to be firing. (with the hot wire, she shows reduced voltage at the coil, the ,6 ohm resistor gets hot, but still no go).

she's got no blown fuses. the starter turns over with the key, and all thick wires at the solenoid all have power, though neither of the smaller violet and red wires coming from the solenoid have power with the key in the 'on' position (i have no idea if they're supposed to).

i'd really love some input as to how i'm supposed to diagnose whether my problem is with my ignition switch, starter solenoid, or somewhere in between.

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

bump...i bet somebody can save me hours of diagnostic wire-chasing...could sure use some help!

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

sounds like the element in the resister is cracked. Have you tried to hot wire after the resister. That will work for a short time before the coil heats up.

there's no voltage on the input side of the resistor, though....so i think the problem's further upstream...

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

Then put a test lamp on it and go play with the ignition sw and fuse #1 while watching the lamp. The ign feed comes from a terminal on the light sw.

You also might want to look around under the dash..some PO may have installed a kill sw.

__________________
A Dalton

Well, no amount of fiddling with the key, ignition switch, or #1 fuse will get me any power there at the starter resistor.

New things discovered:
*If I jump a hot wire to the little violet-colored wire that's screwed to the starter solenoid, I DO get power at the resistor (even with the key OFF) and she turns over.
*There are (2) wires (brown/grey and brown/green) that are attached to a separate little fitting on the side of the ignition switch...which I believe is the "Key In Buzzer Switch." Strangely, there are a couple previous-owner-added wires tied into this "Key In Buzzer" wiring, (which appears to be the lighting system and dead-end with a bunch of PO-added/disconnected/taped wires)....Any idea what this would be for? Car alarm maybe? It doesn't appear to connect to any ignition wiring...hmm.

I'd love some advice on where to focus and how to test my components. With the wires off the back of the ignition switch, are there any particular terminals I can jump which will serve as a test for the switch + solenoid?

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

Got the benz circuit diagrams? They're drawn with current flow in mind.

You can start at the 12v lead on the battery for any circuit and follow how the current flows back to ground.

As I recall from memory after a long day, you're looking at current going from the battery to the #1 fuse to the ignition switch turned to starter mode (#2 position on your dash) to the neutral safety switch to the both the starter and the junction point between the two resistors (bypassing only the first one). Separately, there is a current path from the switch to the first balast resistor.

That second current path should always be active when the key is turned away from position #0. The first current path I mentioned is only during starting.

Been a long day, so try and match what I said to the schematics.

-CTH

__________________
- cth350@gmail.com
http://www.111lakeside.com/

well, if i'm readin' everything right, it sounds like the problem would NOT be caused by the starter/solenoid, since the starter always engages with the key, and the voltage it passes along to the resistors is only important during "extra cold" conditions. true?

however, my diagram (for the 280e and the 250) makes it seem like although power for the ignition switch comes in from fuse 1, one of the starter circuits is tied into fuse 4, and the starter resistor is tied into fuse 12.

since my headlights work and my starter engages with the key switch, i've got to assume there's power getting to the ignition switch properly, but it's just not getting out somehow from there to the coil? problem is, i can't find/identify the wire that serves that purpose! if i could, i imagine i could just jumper a hot wire to it, see if it fixes the problem, and know for sure that the ignition switch is bad, right?

of course, my worry is that i've got a loose/corroded ground or something somewhere....gotta be related to the fact that the car's been sitting for a couple years.

ideas?

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

KILL SWITCH!
(kudos, mr. dalton).

spoke with Mike D on the phone this mornin' and he helped me eliminate some stuff. twisted myself into a seriously contorted position with a flashlight in my teeth, and was able to find a couple wires spliced into the red/black ignition wire near the fusebox/firewall penetration. followed the splice to the DOME switch in the dash. flipped it, and tadaa. pretty sneaky! amazed the PO didn't inform me. just amazed. thanks all!

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

Good job Lee! Way to stick with it. When it comes to wiring, the only thing to do is follow it from source to end.

Ya know, the owner may not have been aware that he had a "kill switch" built in. It's very possible whoever wired in his alarm system just "grabbed" what they thought was a ground or hot wire and wired it in not realizing the status of the circuit/wire changed when the switch was flipped. Most American mechanics still haven't grasped the European concept of a "switched" ground for control of electrical devices.

A case in point is the defroster motor connection for the W114's. Power is supplied to the motor. The speeds are varied by switching the ground connections. This allows power to only have to be supplied to the device and the remote switch is non-powered. No chance of an "in-dash" short and fire.