Does this sound like an ignition switch failure? - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 02-27-2014, 10:47 AM Thread Starter
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Thumbs down Does this sound like an ignition switch failure?

Vehicle is a 1970 280S. After getting my stupid question about ohm resistance answered, I can now request help with the rest of the problem. I have a Hot Spark unit in the car. Installed after I fried(I think) my Pertronix unit(that's another story). Car would not start. I hooked a test light to the coil terminals and when the ignition switch is turned on the light comes on for just a second before the switch is fully opened and then goes out just before the starter is engaged. This has been driving(pun intended)me nuts and this is as close to a solution as I have come to. Sounds like the switch....yes? If not then what else should I be looking at.....? If it is the switch, how do I remove the back section? Can it be done without having to remove the entire housing/steering lock and all? I assume, if it is the switch, the problem is with the electrical portion and the tumbler assembly is not part of the problem. I have the CD but it is useless in this area. Any help/pics would be appreciated and I thank all in advance for any help provided.
dws


1973 Mercedes 450SLC (PineGreen/MahoganyLeather)
1981 Mercedes 380SL FORSALE (LtIvory/PalominoMBTex)
1984 Mercedes 500SEC Euro (040Black/BlackLeather)
1992 Mercedes 300SL-24 Signal Red/Black Leather
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post #2 of 6 (permalink) Old 02-27-2014, 05:03 PM
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What are the symptoms when you are trying to start the car? Do you have a voltmeter?

When the key is first turned on, there will be a very brief in rush of current to charge the coil. If you are right across the coil, the coil appears as a short, and should go up as it charges. So, the test light, I would expect to turn on as time goes on. The interval for this, is very short. ms.

Also, if I remember right, you wire the pertronix somewhat different than if it was points. In other words, points opens and closes to ground, and I think the pertronix is designed to short across the coil.


I can't help on the switch, though, I just replaced mine. I think it was about $240 for the switch. Ouch.

If you think it's the switch, it's possible to temporarily bypass the switch, whcih is what I did. I even had a remote starter switch.

Hope that helps.

-- brett
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post #3 of 6 (permalink) Old 02-27-2014, 05:24 PM Thread Starter
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Quote:
Originally Posted by NorCalSL View Post
Vehicle is a 1970 280S. After getting my stupid question about ohm resistance answered, I can now request help with the rest of the problem. I have a Hot Spark unit in the car. Installed after I fried(I think) my Pertronix unit(that's another story). Car would not start. I hooked a test light to the coil terminals and when the ignition switch is turned on the light comes on for just a second before the switch is fully opened and then goes out just before the starter is engaged. This has been driving(pun intended)me nuts and this is as close to a solution as I have come to. Sounds like the switch....yes? If not then what else should I be looking at.....? If it is the switch, how do I remove the back section? Can it be done without having to remove the entire housing/steering lock and all? I assume, if it is the switch, the problem is with the electrical portion and the tumbler assembly is not part of the problem. I have the CD but it is useless in this area. Any help/pics would be appreciated and I thank all in advance for any help provided.
dws
But wait, there's more.....I neglected to add that I also have trouble with the ignition 'running on'. In other words, the starter will continue to grank the engine even if I turn the key all the way to the left and remove it! I'm waiting for the proper coil to come in and in the meantime pulled the one from my '73 SLC with the correct resistance and still no start. So all this plus my initial inquiry adds up to a wonky ignition switch to me. What do you all think?
dws


1973 Mercedes 450SLC (PineGreen/MahoganyLeather)
1981 Mercedes 380SL FORSALE (LtIvory/PalominoMBTex)
1984 Mercedes 500SEC Euro (040Black/BlackLeather)
1992 Mercedes 300SL-24 Signal Red/Black Leather
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post #4 of 6 (permalink) Old 03-02-2014, 08:54 PM
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From your description, I'd concur with the ignition switch. They're modular; the lock cylinder fits into the steering wheel immobilizer mechanism, with the switch screwed onto the back, where the wiring harness plug attaches.

It's a DIY job, about 3 of 10 bananas. The part was $80.00 for me a few years ago. You'll probably have to pull the steering wheel and the instrument cluster.

Disconnect the battery, you'll be messing around with the power, so just 'safe' the system as a matter of course. you're already having problems with the switch, so let's not push our luck.

Get a piece of 2 x 4 long enough to go from one of the steering wheel spokes to the floor, to keep the wheel from turning. Put a shop rag on the end to keep from marking up the wheel.

Pull the center cover from the wheel to expose the Big Nut In The Center That Holds The Wheel On (technical term, sorry). Put key in ignition and unlock the steering wheel. Get a large socket on the nut, and working against the 2 x 4, loosen and remove the nut. I have to use a 1/2 in drive with a breaker bar the first time. You want to work against the bracing of the 2 x 4, DO NOT work against the steering wheel lock. It is more likely that you will damage the lock mechanism before the nut loosens. This is expensive and a lot of hassle to replace. Trust me on this, a piece of 2 x 4 and a shop rag are a LOT less of a cost and hassle.

The wheel should pull straight off toward you.

The cluster is held in by a rubber band around it, it's a friction fit. You might be able to wiggle it out, but if not, the usual process involves a couple of wire hooks, about 8 inches long, with a 1/4" bend at the end. you slip the hooks in , turn them 90 degrees to get the hooks behind the cluster, and pull.

There are a few electrical connectors, the speedometer cable, and the oil pressure guage tube on the back of the cluster, so pull gently, until you can clear enough space to unscrew the speedo cable, disconnect the electrical connectors, and remove the oil pressure tube. This requires a 10mm open end wrench. the cluster should then be free.

The back of the locking mechanism should be visible now. You can pull the large connector off the back, and move it out of the way. There are 3 flat head screws holding the switch to the lock mechanism that need to be removed. Depending on your body style, you may need VERY short driver to get at them (107), but other bodies have more room to work in there. The switch module should be easily replaceable with the screws removed, just be patient to make sure everything is aligned.

While you're there, there are a few things to check out:

Replace any burned out bulbs in the cluster.

Many people recommend adding an additional ground lead from the instrument cluster to the body of the car. If you do, put connectors in, so the lead can be separated in the future.

Check the pivot points for the windshield wipers, if you can see them. One of mine had come loose, the arm dropped down and damaged the insulation on my light switch. Some people recommend removing the bolts. putting Loc-tite on them, and replacing.

Check around for anything else in there that should be addressed; loose connectors, bare wires, poorly routed aftermarket alarm wires, dead wombats, demon infestations, etc...

Reassemble in reverse order.

--------------------------------------------------------------------------------------------

DO NOT ATTEMPT TO START VEHICLE WITH CLUSTER OUT!!!!!!! The oil pressure guage is a manual device, and if you try to start the vehicle with the cluster out, you will have a pressurized tube full of oil aimed at your chest: NOT a Good Thing.

--------------------------------------------------------------------------------------------

When reinstalling steering wheel, there is no need to Loc-tite the Big Nut. That's what made it so hard to remove in the first place. there really isn't enough stress to warrant it, just tighten firmly, against the 2 x 4, and you're good.

Then remove the key from the lock cylinder, reattach the battery, and start the vehicle. If your problem was the switch, you've fixed it.

Now go grab a celebratory adult beverage and look back on a job well done.

--------------------------
I don't know what your experience level is, so I just entered a complete how-to for most anyone to follow. If you don't need it, someone else may in the future.

Remember: It's not just a car. It's an Adventure.
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post #5 of 6 (permalink) Old 03-03-2014, 08:30 AM
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if you are not sure it s the switch , easy to test under the hood , you could unplug the ignition sw , and connect another and use a screw driver to turn on and see .either you have power at ignition system under hood with key on , or you dont , not hard to figure out .now , the steering lock mechanism is bullet proof , you can put all your might on it , and not damaging it .
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post #6 of 6 (permalink) Old 03-03-2014, 10:12 AM Thread Starter
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Date registered: Jun 2007
Vehicle: '70 280S-'73 450SLC-'81 380SL-'84 500SEC Euro-'92 300SL24-'95 E320
Location: Northcoast of Ca in Eureka
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Quote:
Originally Posted by RadioTek View Post
From your description, I'd concur with the ignition switch. They're modular; the lock cylinder fits into the steering wheel immobilizer mechanism, with the switch screwed onto the back, where the wiring harness plug attaches.

It's a DIY job, about 3 of 10 bananas. The part was $80.00 for me a few years ago. You'll probably have to pull the steering wheel and the instrument cluster.

Disconnect the battery, you'll be messing around with the power, so just 'safe' the system as a matter of course. you're already having problems with the switch, so let's not push our luck.

Get a piece of 2 x 4 long enough to go from one of the steering wheel spokes to the floor, to keep the wheel from turning. Put a shop rag on the end to keep from marking up the wheel.

Pull the center cover from the wheel to expose the Big Nut In The Center That Holds The Wheel On (technical term, sorry). Put key in ignition and unlock the steering wheel. Get a large socket on the nut, and working against the 2 x 4, loosen and remove the nut. I have to use a 1/2 in drive with a breaker bar the first time. You want to work against the bracing of the 2 x 4, DO NOT work against the steering wheel lock. It is more likely that you will damage the lock mechanism before the nut loosens. This is expensive and a lot of hassle to replace. Trust me on this, a piece of 2 x 4 and a shop rag are a LOT less of a cost and hassle.

The wheel should pull straight off toward you.

The cluster is held in by a rubber band around it, it's a friction fit. You might be able to wiggle it out, but if not, the usual process involves a couple of wire hooks, about 8 inches long, with a 1/4" bend at the end. you slip the hooks in , turn them 90 degrees to get the hooks behind the cluster, and pull.

There are a few electrical connectors, the speedometer cable, and the oil pressure guage tube on the back of the cluster, so pull gently, until you can clear enough space to unscrew the speedo cable, disconnect the electrical connectors, and remove the oil pressure tube. This requires a 10mm open end wrench. the cluster should then be free.

The back of the locking mechanism should be visible now. You can pull the large connector off the back, and move it out of the way. There are 3 flat head screws holding the switch to the lock mechanism that need to be removed. Depending on your body style, you may need VERY short driver to get at them (107), but other bodies have more room to work in there. The switch module should be easily replaceable with the screws removed, just be patient to make sure everything is aligned.

While you're there, there are a few things to check out:

Replace any burned out bulbs in the cluster.

Many people recommend adding an additional ground lead from the instrument cluster to the body of the car. If you do, put connectors in, so the lead can be separated in the future.

Check the pivot points for the windshield wipers, if you can see them. One of mine had come loose, the arm dropped down and damaged the insulation on my light switch. Some people recommend removing the bolts. putting Loc-tite on them, and replacing.

Check around for anything else in there that should be addressed; loose connectors, bare wires, poorly routed aftermarket alarm wires, dead wombats, demon infestations, etc...

Reassemble in reverse order.

--------------------------------------------------------------------------------------------

DO NOT ATTEMPT TO START VEHICLE WITH CLUSTER OUT!!!!!!! The oil pressure guage is a manual device, and if you try to start the vehicle with the cluster out, you will have a pressurized tube full of oil aimed at your chest: NOT a Good Thing.

--------------------------------------------------------------------------------------------

When reinstalling steering wheel, there is no need to Loc-tite the Big Nut. That's what made it so hard to remove in the first place. there really isn't enough stress to warrant it, just tighten firmly, against the 2 x 4, and you're good.

Then remove the key from the lock cylinder, reattach the battery, and start the vehicle. If your problem was the switch, you've fixed it.

Now go grab a celebratory adult beverage and look back on a job well done.

--------------------------
I don't know what your experience level is, so I just entered a complete how-to for most anyone to follow. If you don't need it, someone else may in the future.
Thank you so much for your reply. I am mechanically inclined and have had the steering wheel and cluster removed before. Knowing I can get at the switch through the cluster opening is a whole lot better than having to lay on my fused back and look up. Great detailed response and I thank you again, exactly what I was looking for.
david


1973 Mercedes 450SLC (PineGreen/MahoganyLeather)
1981 Mercedes 380SL FORSALE (LtIvory/PalominoMBTex)
1984 Mercedes 500SEC Euro (040Black/BlackLeather)
1992 Mercedes 300SL-24 Signal Red/Black Leather
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