72 250 starting/wiring Qs - PeachParts Mercedes-Benz Forum

mzsmbs · #1 08-07-2003, 05:34 PM

Hi all,

Ok, let me start with some basic info on my 72 250; it is M130.016, W114.011.

The original symptoms were as follows: the car died one day warming up in the garage. The red light in the dash, the one for the ignition system, came on around that time. I say around because it may have come on just before it died; it has been a while so I can’t recall. The car would turn over and fire when the ignition key was in the ‘start’ position. As soon as the key returned to ‘run’ the car would go silent. After posting some questions on Stu’s list (good people, not many w114 owners) the answers led me to the resistor blocks which one of I found to be dead. (silver wrap, .6)
I replaced it and tried to restart the car. Nothing happened. The motor turned over but no fire. So now I lost the spark. Trying to figure out on what is up I started to trace all the wires in the ignition circuit. The new resistor seems to be fried now too (the blue resistor reads 40 ohms on the x1K scale and the silver one reads 0.) Surely all of this info is left out of the Haynes’ diagrams.

This is how my wiring runs: An orange/black wire runs from fuse #2 to the blue resistor (.4), from the other side there are two wires, the red/white one runs somewhere back into the harness? and the red one goes to ignition module (under the battery) (15), the black wire (center and (16)) goes to silver resistor (.6) and then on to the (+) of the coil, the coil’s (-) is grounded, the green/yellow wire (7) from the ignition module runs via a junction to the distributor where it joins the condenser, of course everything is grounded a whole bunch. I have continuity in all these wires.

I saw that you guys have discussed some of this in April but not exactly what I need.

Q1: is my wiring connected correctly, especially the resistors?

Q2: why would the resistor fry out?

Q3: can I jump around all these things and go from coil (-) straight to the distributor/condenser without frying anything out? Just to test the rest of the system.

Q4: could the problem be with the ignition module? Can it be tested?

Any and all of your comments are appreciated, and if anyone has and is willing to share the correct diagrams, pm me please. I am stuck.

Thanks

mzmzmzmzmmzmz

ctaylor738 · #2 08-07-2003, 06:47 PM

Hmm.

The basics of this are as follows:

1. 12V from the Start position directly to + on the coil to give a good hot spark when cranking

2. 12V from Run to the first resistor, which knocks it down to 6, then to the second, so its about 2.5V when it goes to + on the coil. The ignition module enables a hot spark with the reduced voltage which extends point life.

I don't see how anything can work if - on the coil is directly grounded. It is the momentary un-grounding when the points open that causes the coil to fire.

You should be able to run 12V to your good resistor and from the other side of the resistor to + on the coil and get the engine to run briefly without hurting anything.

My wiring diagram does not show the ignition module and the two resistors - just a single resistor and the coil. My 250C has a Crane unit, so that won't help.

psfred · #3 08-07-2003, 07:41 PM

Coil should be grounded through the transistor box, not through the points.

A fried resistor makes me think bad transistor switch box with "monkeyed" wiring to bypass it.

If the wiring is anything like the 280 SE, the point lead can be connected directly to the coil instead of to the transistor box.

I don't have a readable wiring diagram, sorry (that is to say, I have one, but I can no longer read it due to middle age short arm disease....)

Peter

ctaylor738 · #4 08-07-2003, 08:46 PM

I need to see Herr Fuchs about my 300E's stalling tomorrow. I will see if he has a schematic of the ignition with the CD unit.

gmask · #5 08-08-2003, 12:51 PM

Quote:

Originally posted by mzsmbs
Ok, let me start with some basic info on my 72 250; it is M130.016, W114.011.

I'm afraid I can't offer much help but I have a 72 250 and your engine is a 130.923 .. there is no such engine as a 130.016.

Since sounds like parts are getting fried you will definately want to diagnose the problem before putting any more new parts in there.

I may beable to poke around and trace some wires for you on my car for whatever good it might do.

Otherwise as far as I know the major components are the resistors, coil and transistor box located under the battery tray.

The only thing that I know about the transistor box is that they are not repairable..at least not easily. Maybe you could remove it and have a local shop test it?

mzsmbs · #6 08-09-2003, 03:03 PM

Quote:

I'm afraid I can't offer much help but I have a 72 250 and your engine is a 130.923 .. there is no such engine as a 130.016.

gmask / everyone,

130.016.26.01 is stamped right on the block! Whatever the motor is, it is inline 6, 2 carbs.

anyway, if you could look under your hood and check the way the wiring runs through all those points (coil-resistors-ignition box-distributor), seems like that could be the problem. If the wiring is the same as I described in my first posting, that will point to the box or something in the line up.
I would very much appreciate it as I am at the end of my wit on this and I don't have a reliable indy. I might head to my fav part store, here in a few, where they might help.

thanks to everyone who has responded.

mzmzmzmzmzmz

gmask · #7 08-09-2003, 03:22 PM

>>>130.016.26.01 is stamped right on the block! Whatever the motor is, it is inline 6, 2 carbs.

Yeah that's the blocks part number... so it starts with 130 but the rest describes the part.

I'll try to trace of my connections for ya this weekend.

Adrian

mzsmbs · #8 08-09-2003, 03:30 PM

gmask,

Thanks for that info. it is good to know the right numbers for my motor. Also, thanks for looking under your hood.
take care

mzmzmzmzmz