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I need help with a mystery on my car (Electrical)

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I have a new to me 1989 190e 2.6 33k miles. There is a wire (aftermarket) that is coming out of the fuse box and I am trying to figure out what this is for and why would it be there.

1. Red wire starts at fuse 19 and goes across the car at the firewall. It terminates in the relay behind the battery. I am not sure what the relay is. My assumption is that the "jumper" wire is energizing the relay because it is not getting its own power through the socket. But I am not sure. There are 2 other parts to this mystery that I will add to the post later but I want to try and figure this out first. This car sat a lot of its life and did have some known rodent damage.

The car had a fully installed car phone and an aftermarket stereo, other than that... stock.

What do you guys think this could be for?

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1986 190E 2.3-16, 200k mi
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That's weird, have you pulled up the relay to see where the wire terminates? The grommet going behind the passenger side of the dash is right behind there so I would guess someone may have just used the relay as a dodgy "clamp"?
 

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2002 Mercedes Benz ML 320
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415 Posts
I have a new to me 1989 190e 2.6 33k miles. There is a wire (aftermarket) that is coming out of the fuse box and I am trying to figure out what this is for and why would it be there.

1. Red wire starts at fuse 19 and goes across the car at the firewall. It terminates in the relay behind the battery. I am not sure what the relay is. My assumption is that the "jumper" wire is energizing the relay because it is not getting its own power through the socket. But I am not sure. There are 2 other parts to this mystery that I will add to the post later but I want to try and figure this out first. This car sat a lot of its life and did have some known rodent damage.

it probably also had a poorly installed, aftermarket alarm

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1989 W201 190e 2.6
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70 Posts
Discussion Starter · #4 ·
That's weird, have you pulled up the relay to see where the wire terminates? The grommet going behind the passenger side of the dash is right behind there so I would guess someone may have just used the relay as a dodgy "clamp"?
I will pull the relay and see what pins are jumped. I think this is the fuel pump relay. And after going to YouTube university... I think this is an ignition activated jumper as a temporary solution to replacing the relay. Can someone tell me what the normal operation of the fuel pump is? Most cars I am used to will run the pump for about 8-10 seconds and then it stops when pressure is reached. This one seems to run continuously when ignition is on. That could be normal but I am not sure. Please let me know, thanks.
 

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1989 W201 190e 2.6
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70 Posts
Discussion Starter · #5 ·
@Former Repair Manager
I checked recent service records and there was a receipt where the customer concern was "Aftermarket alarm system was going off for no reason in the middle of the night."
The shop performed a removal of the aftermarket alarm system. Also, the shop advised customer of the "Custom" fuel pump wiring. That service record was from 7k miles ago. It looks like the wiring was never sorted.
 

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2002 Mercedes Benz ML 320
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415 Posts
Most aftermarket alarms have a feature to engage a fuel pump cut off when the alarm is activated, this feature helps prevent a person from driving away in a stolen car. I have found that many of the so-called installers of the alarm systems are poorly trained high school dropouts I have seen very sloppy work over the years when it concerns installation of alarm systems, I know one individual in my local area who I trust to properly install an aftermarket an alarm he is so good that he could teach at the university level if courses were offered to install vehicle alarm systems properly I suspect yours was not so carefully installed and not so carefully removed from the vehicle
 

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1989 W201 190e 2.6
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70 Posts
Discussion Starter · #7 ·
More to the mystery, There is a black wire coming from Fuse 20 and going straight to the coil (at least I think it is the coil). Here are some pics of that. If that is not the coil please let me know what that is. Thanks Eric

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1989 W201 190e 2.6
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70 Posts
Discussion Starter · #9 ·
The last part of the mystery is this component. Can anyone tell me if this factory or aftermarket? It burned and there are missing connections.

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2002 Mercedes Benz ML 320
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415 Posts
Definitely aftermarket alarm probably not a viper product probably lower end of the spectrum of quality aftermarket alarms. A vapor installation would be a lot cleaner providing it was done by the correct installer technician. I would locate a reputable alarm shop and pay them to remove the components left behind you may want to consider having a viper system installed.
 

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1989 W201 190e 2.6
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Discussion Starter · #11 ·
Definitely aftermarket alarm probably not a viper product probably lower end of the spectrum of quality aftermarket alarms. A vapor installation would be a lot cleaner providing it was done by the correct installer technician. I would locate a reputable alarm shop and pay them to remove the components left behind you may want to consider having a viper system installed.
Good suggestions. I don't think I will put an alarm back in this car though. This is garaged and only a weekend brunch cruiser 🍷
 

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1990 Mercedes 190E 2.6
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104 Posts
I have the same thing on mine.... if I disconnect this wire... will the car still run? IDK... may be a stupid question... I think the alarm was with the original radio?? in that wiring ? but I put a bluetooth in to update for my purpose.. still have the original if someone needs it... thanks.
 

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190e 2ltr Sportline, 1990 auto
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this is after market ,I have never seen a fuse used like this before, the black box is also after market and might be related to a alarm fitted,remove the fuse and see what stops working,
It might be for a fuel pump shut off or a ignition isolate, ,
 
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