Electrical ignition problem - PeachParts Mercedes-Benz Forum

mbzak · #1 05-05-2011, 09:29 PM

Something has caused the ignition switch wire to fail in making enough voltage to power the alternator. It's getting under 12, more like 11 or just under because of excess resistance. Even with a charger on the battery pulling 16V for the entire system that wire is staying the same low with the ignition on. So it seems likely to be the ignition switch if it's not a corroded wire. But I know that between the alternator and the ignition it runs through the ABS system and I wonder if that might also be a cause for fault.

My old alternator was just about shot so I am replacing it anyway, and going with the 90A over the 70. But this problem happens instantly, literally the system was making 13.8V running and the next start the dash lights won't go off and the alternator isn't powered. There's a clue in that this happened once before where the lights stayed on for awhile after starting but then went off shortly after.

scottmcphee · #2 05-05-2011, 11:20 PM

Where is the ignition switch in a diesel?

mbzak · #3 05-05-2011, 11:30 PM

Quote:

Originally Posted by scottmcphee

Where is the ignition switch in a diesel?

Yo watup Scotty, muzak from VO. Ignition switch is on the column behind the wheel, could just be corrosion there building up resistance but something tells me the ABS link may be involved too.

Diesel911 · #4 05-06-2011, 01:29 AM

Quote:

Originally Posted by scottmcphee

Where is the ignition switch in a diesel?

If it is not an Ignition Switch what name do you have for it?

vstech · #5 05-06-2011, 11:28 AM

Quote:

Originally Posted by Diesel911

If it is not an Ignition Switch what name do you have for it?

starter engage and glow plug control with vacuum directional key operated mechanism?

vstech · #6 05-06-2011, 11:30 AM

is it possible the wire you are measuring is the voltage sense wire that passes through the bulb as a resistor... resulting in a lower measured voltage?

mbzak · #7 05-06-2011, 12:45 PM

Quote:

Originally Posted by vstech

is it possible the wire you are measuring is the voltage sense wire that passes through the bulb as a resistor... resulting in a lower measured voltage?

On the same bar where the main B+ and Ignition wires connect, there's 2 smaller wires that connect together from the ignition side 1 blue and 1 blue/red, and the D+ alternator wire also connects. Perhaps 1 blue is the bulb? But 1 has to carry juice to the alternator- either way the alternator isn't getting enough V to make juice.

mbzak · #8 05-06-2011, 09:51 PM

Here's the charging diagram from my CD manual: I worked backwards from the ignition switch and found it's OK. The fault has to be pre the X4 poles where the Voltage has dropped which puts the fault to the warning light indicators that are still a mystery to me. As was mentioned earlier there is some resistance from the bulb and that's why I assume there's 2 wires at the X4 pole, the solid blue 1 the warning bulb, blue/red carries full V to the alt. What I'd like to know is where the blue/red wire comes from since it's not clear here. They both go into the shroud behind the battery which I assume goes to the interior via the passenger side.