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I have a 1991 Mercedes 500sl engine, will not start. Key fob…

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I have a 1991 Mercedes...
I have a 1991 Mercedes 500sl engine, will not start. Key fob does not function. Car has a Radio Alarm Anti-theft system.
Submitted: 2 years ago.Category: Mercedes
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Customer reply replied 2 years ago
I just replaced the engine with a used motor.
Answered in 2 hours by:
2/25/2016
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago
Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 5,864
Experience: 20 years Master Certified excellent fix rate and have access to factory wiring, and instructions.
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Hello, did the engine start and run before you swapped the engines? why did you exchange engines?

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Customer reply replied 2 years ago
The engine did not run. It was locked up. The starter was removed, It looked like it was overheated. It also had a dead battery too. So I did nothing.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

OK so did you replace the engine, and starter as well?

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Customer reply replied 2 years ago
No, This way gives me time to think about what you write...
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok Robert so does the starter crank the engine over ?

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Customer reply replied 2 years ago
it does.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok good. Next step does the engine run if you spray starter fluid ?

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Customer reply replied 2 years ago
no, there is no voltage to the coil with the key on or when the engine is spinning over.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok. Good. Good to know. Is the crank sensor plugged in ? It's the sensor at the rear of the engine on the drivers side on the bell housing.

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Customer reply replied 2 years ago
I'm sure it is, I will have to go look.....
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Also inspect all the wiring , those years had a issue with the wiring harnesses cracking and falling apart. Make sure the wiring does not look brittle.

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Customer reply replied 2 years ago
The sensor is plugged in. On the drivers side fender, right. I have looked at the wiring harness and the only bad wires I see are one to the a/c and to the temp sending units. They must be under the motor mount brackets.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok so far so good. Give me a second.

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Customer reply replied 2 years ago
while I'm waiting, l will say this, with the ignition switch on. The windows do not operate, the horn does not blow the door locks do not operate. The key remote has new batteries, but only shows a red light when pressing the button. I think there should be a green light come on when the doors are unlocked. The first time I tried to start the engine the alarm sounded, I had just connected the battery and when I opened the door, the alarm sounded off. I think at that time I inserted the key into the ignition and the alarm quit. I think, not real sure.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Yes please tell me as much as possible. That tells me the theft protection may be active.

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Customer reply replied 2 years ago
Well, that is what I think, if so, how do I deactivate it. Sorry, most times when I use this site, so many techs want to ask all the questions and make the statements. I think this is most of what I can help you with.
Customer reply replied 2 years ago
Oh, another thing. With a test light is connected to the plus side of the battery. It lights up when touching either post on the coil, the light will come on....
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Oh no brother this is a relationship. We both need input to make it work. I need as much info to help you. That way we don't waste time going over things you may have already done.

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Customer reply replied 2 years ago
OK, thanks,
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Currently I am looking over the diagrams fyi

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Customer reply replied 2 years ago
ok
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok check fuse 5 in the fuse box for power. That fuse supplies power when the key is on.

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Customer reply replied 2 years ago
Ok, let me be sure, the fuse box is under the drivers side hood hindge.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Correct

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Customer reply replied 2 years ago
OK, back to the shop. I'll be a few minutes.........
Customer reply replied 2 years ago
no voltage at; numbers 1-2-3-5-6-7-8-13-14-15-16--B
voltage at; numbers 4--A-C-D-E-F-G-H
Customer reply replied 2 years ago
Ignition switch is on while testing....
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok good man. Give me a second

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

When you turn the key in the ignition does it move smooth with good clicks at 2 positions Before you crank ?

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

See if you can press your test light into fuse 5 and wiggle the ignition key on and off and see if it lights up. I think we may have a ignition switch issue. Cause those fuses are key on power. And they come from the ignition switch. So far from what I see. The old diagrams are not as friendly

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Customer reply replied 2 years ago
It turns very difficult. I almost could not get the key inserted. I sprayed WD-40, which helped alot, but still does not turn smoothly.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok. Can you access the bottom of the ignition switch? Or back of it ? I have to see what style you have

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

But try the wiggle test I am betting the switch is faulty and the internals came apart

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Customer reply replied 2 years ago
I will, I will have to wait til Monday to do that. Actually I concidered that the switch may be the problem. I will get the info for you. Until then thanks. A tip will be coming your way.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Appreciate it. On a side note. Fuse 6 is a battery power fuse. So it should have voltage. Is the fuse ok and. It blown ?

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Wait. Hold on that

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Customer reply replied 2 years ago
OK on #6, I wasn't sure if I was on the hot side or the other side of the fuses
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok I was looking at fuse 6 of the rear fuse box. So you are saying fuse 6 now has power ?

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

So if you are testing the fuses with the key on test both too sides of each fuse. All or most should have power. On both sides of each fuse. If not the fuse is blown. I don't know how much you know about cars so forgive me. I don't mean to offend.

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Customer reply replied 2 years ago
OK, now you are saying there is a second fuse box behind the one that has a easy to remove cover. The back one then has screws holding the cover on.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

But the statement of "hot side of other side of fuses " does not jive. If the circuit is alive and the fuse is not blown both sides of the fuse will show power.

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Customer reply replied 2 years ago
correct, I only checked one side of each fuse
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok. Check both side of each fuse.

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Customer reply replied 2 years ago
I did not see any blown fuses. Anyhow I will double check the fuse box
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok so far all the fuses that you say do not have power all get power from the ignition switch. And it's hard wired from the switch to the bottom of the fuse box. So if you have no power at the fuses then the ignition switch (or the power to the ignition switch which I am looking for ) is bad.

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok. Check the battery in the trunk. If should have a big red cable and a few small red cables on the positive connection. Make sure they are all tight as I think there are two nuts if I remember correctly.

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Also the head lights should come on with key or no key

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Customer reply replied 2 years ago
OK, I will check this out. The battery plus side does have two nuts. Not sure about how many wires. I will check the ignition switch too.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok let me know. That may be the issue. Either the battery or the ignition switch. Hope this information helps. Please take a second and click the box and rate my service GOOD OR EXCELLENT SERVICE if you feel I have been helpful and please request me in the future. If you feel I have not been helpful please DO NOT RATE BAD OR POOR AND WASTE YOUR MONEY , I will opt out to see if another expert can provide more or better assistance so you're not wasting your money!!. Thanks for choosing just answer. Lou. also , if you feel i deserve one , BONUSES are GREATLY APPRECIATED ! 😉 Keep in mind then when you rate it does not end our conversation. you can still return here to me for follow up information if needed, Lou.

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Customer reply replied 2 years ago
I was not offended. I have seen fuses corroded at one end before. Anyhow all that checked out. The battery has two red 10 gage wires along with a main heavy wire.
I disconnected the wire harness plug from the ingition switch. While looking up at the plug with 7 pins on the right side with #3 from top is hot as it the #7. On the left side has one hot wire #6. And #6 fuse in the fuse box has no voltage.
The bottom of the ignition switch makes a 90 degree turn into the steering column.
But, beyond that I read that ignition switches in this car can be troublesome. Can you give me any tips?
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ok a later later I can access the diagrams and see what you can check

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Customer reply replied 2 years ago
how to remove the ignition cylinder lock?
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

I will get you the info tomorrow. If you don't hear from me by 10 am shoot me a reminder. Mornings are busy but I don't want to keep you waiting.

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Customer reply replied 2 years ago
Just a reminder
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

Ah sorry about that I have easier access to Mercedes info during the day at night my 2 month old and 2 year old make it harder for me to get to the computer lol. I'll check back in the am. So sorry for the delay.

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Customer reply replied 2 years ago
ok
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 2 years ago

I will have to opt out. My sincere apologies. Hopefully Marty or Pete and assist. This is not typical of me so I apologize for keeping you tied up. Hopefully some one else can get you going. Please do not respond or it will lock your question back to me.

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