Tapping into backup light circuit
05-17-2005, 10:46 PM
#1
Super Member
Thread Starter
Tapping into backup light circuit
I am installing an aftermarket backup sensor into my E500. There are basically three steps to the installation. 1) Connecting the power leads to the backup light circuit, 2) mounting the sensor, and 3) mounting the display indicator inside the passenger cabin. The approach I used for tapping into the backup light circuit should work for any brand aftermarket sensor.
I decided to tap into the left side taillight assembly since there were pre-existing holes (about 25mm diameter) to both the bumper area and the rear window shelf area. The taillights, turn signal lights, brake light, and backup light are permanently installed on the same plastic carrier. If one bulb burns out all bulbs need to be replaced. The turn signal and taillights have redundant bulbs (two each). I understand that these are special long life xenon filled bulbs.
All of the bulbs share the same ground lead which is around the perimeter of the plastic carrier. This ground "trace" is connected to the third pin (brown wire) on the taillight connector. The positive lead for the backup light is connected to the sixth pin (yellow wire) of the same connector. The backup light is the second one from the top.
One approach to tapping into the backup light circuit is to splice into the wires in the cable harness. It's not easy to restore the car to the complete stock setup if you splice into the wiring harness. I used a different approach. The bulb carrier has two male terminal connectors near the top. A 1/4" connector for the ground lead and a 3/16" connector for the brake light positive lead. I assume these are used if you need to tap into the brake light circuit while towing the vehicle. I used the 1/4" connector for the ground lead to the backup sensor. I modified a standard automotive connector by soldering a 5/8" length of a 4-40 brass screw where you would normally crimp the wire. I cut off one of the locating pins near the backup light. I drilled a hole through the plastic carrier and ran a 4-40 tap through the hole in the plastic and the existing hole in the positive backup light trace. I used a 4-40 nut on both sides of the plastic carrier with a flat washer and lock washer on the trace side. The photo shows the blue insulation on the connector, but, I had to remove this since it shrunk when I soldered the brass screw in place. I replaced the blue plastic insulation with a short length of clear flexible tubing.
If there is enough interest in this thread I will post the details for the sensor and display indicator installation.
I decided to tap into the left side taillight assembly since there were pre-existing holes (about 25mm diameter) to both the bumper area and the rear window shelf area. The taillights, turn signal lights, brake light, and backup light are permanently installed on the same plastic carrier. If one bulb burns out all bulbs need to be replaced. The turn signal and taillights have redundant bulbs (two each). I understand that these are special long life xenon filled bulbs.
All of the bulbs share the same ground lead which is around the perimeter of the plastic carrier. This ground "trace" is connected to the third pin (brown wire) on the taillight connector. The positive lead for the backup light is connected to the sixth pin (yellow wire) of the same connector. The backup light is the second one from the top.
One approach to tapping into the backup light circuit is to splice into the wires in the cable harness. It's not easy to restore the car to the complete stock setup if you splice into the wiring harness. I used a different approach. The bulb carrier has two male terminal connectors near the top. A 1/4" connector for the ground lead and a 3/16" connector for the brake light positive lead. I assume these are used if you need to tap into the brake light circuit while towing the vehicle. I used the 1/4" connector for the ground lead to the backup sensor. I modified a standard automotive connector by soldering a 5/8" length of a 4-40 brass screw where you would normally crimp the wire. I cut off one of the locating pins near the backup light. I drilled a hole through the plastic carrier and ran a 4-40 tap through the hole in the plastic and the existing hole in the positive backup light trace. I used a 4-40 nut on both sides of the plastic carrier with a flat washer and lock washer on the trace side. The photo shows the blue insulation on the connector, but, I had to remove this since it shrunk when I soldered the brass screw in place. I replaced the blue plastic insulation with a short length of clear flexible tubing.
If there is enough interest in this thread I will post the details for the sensor and display indicator installation.
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charlieworton (05-20-2018)
05-18-2005, 11:49 AM
#3
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You bring up some interesting points.
1st, I am disappointed that the whole panel has to be changed if only one bulb goes out. Even if they are long life bulbs, it would be nice to just change the set that goes out and not the whole thing. This is like the early model MLs that if one power window switch broke, you had to change the whole cluster!
2nd. I also saw that the manual showed all the error messages that the MFD can show. A few of them were burned out lights and it also said (spare light being used). this brings me to ask; What is the stop light bulb like? Is there a backup light bulb for it? It does not look like it. I imagine that with the center mounted trunk light and the light on the other side you are still OK until you replace that bulb.
3rd. It looks as if all the bulbs are the same. So, if the blinker, reverse and stop lights are usually 21 Watts in intensity, (as well as the rear fog light), how are the driver's side bulbs at 10W intensity for normal parking lights? Are they dimmed for the normal parking light setting and then brightened up for rear fog light setting? My other Mercedes cars always had an unused part in their taillight for the rear fog light. The more recent models have used what I thought were dual filament bulbs for parking lights so that they could double as rear fog lights. Also, it always was only one bulb for the rear fog light, but the W211 uses both bulbs. In you picture they look like a single filament bulb, so that is why I am guessing that they are dimmed.
4th. It is also good to see that they put an amber color plastic between that blinker bulbs and the clear taillight lens. They used to paint the bulb itself. This caused two problems. People would replace them with regular white bulbs and force them to fit and the paint/coating on the bulbs would peel off with time anyway and you would barely have an amber color turn signal. I think this design is much better.
If you have any insight on any of these points and questions, please reply. Also, if you could also show a picture of the inside module and how you mounted it I would be interested in seeing it.
Steve A
1st, I am disappointed that the whole panel has to be changed if only one bulb goes out. Even if they are long life bulbs, it would be nice to just change the set that goes out and not the whole thing. This is like the early model MLs that if one power window switch broke, you had to change the whole cluster!
2nd. I also saw that the manual showed all the error messages that the MFD can show. A few of them were burned out lights and it also said (spare light being used). this brings me to ask; What is the stop light bulb like? Is there a backup light bulb for it? It does not look like it. I imagine that with the center mounted trunk light and the light on the other side you are still OK until you replace that bulb.
3rd. It looks as if all the bulbs are the same. So, if the blinker, reverse and stop lights are usually 21 Watts in intensity, (as well as the rear fog light), how are the driver's side bulbs at 10W intensity for normal parking lights? Are they dimmed for the normal parking light setting and then brightened up for rear fog light setting? My other Mercedes cars always had an unused part in their taillight for the rear fog light. The more recent models have used what I thought were dual filament bulbs for parking lights so that they could double as rear fog lights. Also, it always was only one bulb for the rear fog light, but the W211 uses both bulbs. In you picture they look like a single filament bulb, so that is why I am guessing that they are dimmed.
4th. It is also good to see that they put an amber color plastic between that blinker bulbs and the clear taillight lens. They used to paint the bulb itself. This caused two problems. People would replace them with regular white bulbs and force them to fit and the paint/coating on the bulbs would peel off with time anyway and you would barely have an amber color turn signal. I think this design is much better.
If you have any insight on any of these points and questions, please reply. Also, if you could also show a picture of the inside module and how you mounted it I would be interested in seeing it.
Steve A
05-18-2005, 01:12 PM
#4
Super Member
Thread Starter
Taillight assembly
Fortunately the bulb sub-assembly is less than $50 to replace. It's crazy that the plastic front license plate bracket costs more.
There is only one stop light. I agree with your conclusion that the trunk and opposite side brake light are the "spares".
All of the bulbs *look* the same in the photos, but there are at least two different part numbers on the bulbs. I did not bother to record the bulb part numbers because they are obviously not an available FRU.
BTW, it's necessary to remove the entire taillight assembly in order to remove the light panel.
I will post some photos of the rest of the installation over the next few days as I complete the work.
There is only one stop light. I agree with your conclusion that the trunk and opposite side brake light are the "spares".
All of the bulbs *look* the same in the photos, but there are at least two different part numbers on the bulbs. I did not bother to record the bulb part numbers because they are obviously not an available FRU.
BTW, it's necessary to remove the entire taillight assembly in order to remove the light panel.
I will post some photos of the rest of the installation over the next few days as I complete the work.
Originally Posted by SAguirre
You bring up some interesting points.
1st, I am disappointed that the whole panel has to be changed if only one bulb goes out.
2nd. What is the stop light bulb like? Is there a backup light bulb for it? It does not look like it. I imagine that with the center mounted trunk light and the light on the other side you are still OK until you replace that bulb.
3rd. It looks as if all the bulbs are the same. So, if the blinker, reverse and stop lights are usually 21 Watts in intensity, (as well as the rear fog light), how are the driver's side bulbs at 10W intensity for normal parking lights? Are they dimmed for the normal parking light setting and then brightened up for rear fog light setting?
Steve A
1st, I am disappointed that the whole panel has to be changed if only one bulb goes out.
2nd. What is the stop light bulb like? Is there a backup light bulb for it? It does not look like it. I imagine that with the center mounted trunk light and the light on the other side you are still OK until you replace that bulb.
3rd. It looks as if all the bulbs are the same. So, if the blinker, reverse and stop lights are usually 21 Watts in intensity, (as well as the rear fog light), how are the driver's side bulbs at 10W intensity for normal parking lights? Are they dimmed for the normal parking light setting and then brightened up for rear fog light setting?
Steve A
05-19-2005, 10:29 PM
#5
Super Member
Thread Starter
Display indicator and backup sensor installation
I tried mounting the display indicator on the rear window shelf just in front of the window. It looked okay in that location and the cable was easy to route, but, bright sunlight made the LEDs difficult to see. I remounted the display indicator at the center of the rear edge of the headliner. I used the loop side of a Velcro fastener to secure the display to the headliner. This seems to be adequate and does not damage or alter the headliner. It was not necessary to remove the C-Pillar trim panel to route the cable from the trunk to the top edge of the rear window. I was able to slide this trim panel forward just enough to slip the indicator cable behind it. You can see a short length of the cable at the rear edge, but, it's not that objectionable since the antenna on the outside partially conceals this area.
I added the grommet shown in the photo to protect the cable from the raw edge of the hole near the bottom lower left side of the rear window on the inside of the trunk. There were two unused 6mm threaded holes that I used to attach a clip to hold the indicator cable in place. These are probably for one of the options not installed in my E500. It's not too difficult to run a cable from the lower inside corner of the rear window to the trunk area through the existing hole.
I have not decided whether to mount the sensor above or below the crashbar. Each location seems to have pros and cons. I am going to try it in each position for a few days to see which spot works best. There is not much room below the crashbar and I am not certain if the shape of the bumper at the lower edge is ideal for a radar type sensor. The crashbar seems to obscure objects over three feet high if I mount the sensor below the crashbar. I am favoring the area above the crashbar, but I will probably add an additional strip of the 3M Dual Lock fastener so I can move the sensor another 1/2 inch towards the bumper cover. Doing this should provide a clearer "view" of objects near ground level. For anyone planning to install the aftermarket ultrasonic type sensors, it should be relatively easy to do so in the removable trim piece that is just above the crashbar.
I added the grommet shown in the photo to protect the cable from the raw edge of the hole near the bottom lower left side of the rear window on the inside of the trunk. There were two unused 6mm threaded holes that I used to attach a clip to hold the indicator cable in place. These are probably for one of the options not installed in my E500. It's not too difficult to run a cable from the lower inside corner of the rear window to the trunk area through the existing hole.
I have not decided whether to mount the sensor above or below the crashbar. Each location seems to have pros and cons. I am going to try it in each position for a few days to see which spot works best. There is not much room below the crashbar and I am not certain if the shape of the bumper at the lower edge is ideal for a radar type sensor. The crashbar seems to obscure objects over three feet high if I mount the sensor below the crashbar. I am favoring the area above the crashbar, but I will probably add an additional strip of the 3M Dual Lock fastener so I can move the sensor another 1/2 inch towards the bumper cover. Doing this should provide a clearer "view" of objects near ground level. For anyone planning to install the aftermarket ultrasonic type sensors, it should be relatively easy to do so in the removable trim piece that is just above the crashbar.
05-21-2005, 11:09 PM
#6
Super Member
Thread Starter
Location of backup sensor
I experimented with various objects behind the car with the sensor above and below the crashbar. In the E-Class (and probably all other MB models), you cannot shift the transmission into reverse unless the engine is running. I temporarily powered the backup sensor from the trunk mounted accessory socket so I could walk the coverage zone without running the engine. My wife does not have the patience to be an assistant for this type of project.
With the sensor mounted below the crashbar, I was able to detect an object as short as one inch above the ground (metal yard stick on edge). However, the crashbar seems to obscure the signal, and objects at the level of the taillights were not reliably detected.
By moving the sensor to a location above the crashbar, I was able to detect objects up to the height of the trunk lid. I did move the sensor about one half inch closer to the bumper cover than I did the first time I mounted it. The metal yard stick turned on edge could not be reliably detected with the sensor above the crashbar. However, objects three to four inches above the ground could easily be detected. Since the E-Class has good ground clearance I decided it made more sense to mount the sensor in a position where it could detect objects as high as the trunk lid rather than things just above the ground. I have the sensor mounted below the impact foam on my SLK350, and this location does produce an occasional nuisance alarm.
It would be possible to mount a different model sensor between the crashbar and the bumper cover, but this would require removing the bumper cover in order to do the installation.
The W211 model has to be one of the easiest cars in which to install an aftermarket backup sensor. No holes to drill, bumper removal not required, and a pre-existing path to route a display indicator cable between the trunk compartment and the rear window shelf area.
With the sensor mounted below the crashbar, I was able to detect an object as short as one inch above the ground (metal yard stick on edge). However, the crashbar seems to obscure the signal, and objects at the level of the taillights were not reliably detected.
By moving the sensor to a location above the crashbar, I was able to detect objects up to the height of the trunk lid. I did move the sensor about one half inch closer to the bumper cover than I did the first time I mounted it. The metal yard stick turned on edge could not be reliably detected with the sensor above the crashbar. However, objects three to four inches above the ground could easily be detected. Since the E-Class has good ground clearance I decided it made more sense to mount the sensor in a position where it could detect objects as high as the trunk lid rather than things just above the ground. I have the sensor mounted below the impact foam on my SLK350, and this location does produce an occasional nuisance alarm.
It would be possible to mount a different model sensor between the crashbar and the bumper cover, but this would require removing the bumper cover in order to do the installation.
The W211 model has to be one of the easiest cars in which to install an aftermarket backup sensor. No holes to drill, bumper removal not required, and a pre-existing path to route a display indicator cable between the trunk compartment and the rear window shelf area.
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05-23-2005, 07:33 PM
#8
Super Member
Thread Starter
radar backup sensor vs ultrasonic backup sensor
The unit I installed is a Guardian Alert hitch model. It uses radar technology and transmits and receives signals through the plastic bumper cover. The manufacturer seems to focus on fleet sales and does not have much of a retail presence. Even though this particular device is intended to be mounted on a 2-inch receiver hitch, it works fine when installed behind the bumper. The sensor measures 3-inches square by 1.5-inches thick. Not pictured is the adapter for the hitch mount that I did not use. Also, the 3M Dual Lock I used to mount the sensor is not included with the unit. I will confess that in addition to being an MB enthusiast I operate a part time business as an authorized reseller for these backup sensors. I plan to offer an "E-Class kit " which includes everything needed to do a plug and play install. Until mbworld answers my requests about becoming an advertiser/sponsor, I don't think I will discuss any further commercial details. If you want to know more, PM or e-mail me offline.
Originally Posted by steph280
I just realized the sensor in your picture is different than the OEM ones that requires drilling on the bumper. Who makes that unit in your picture?
05-20-2018, 07:17 AM
#10
I used a different approach. The bulb carrier has two male terminal connectors near the top. A 1/4" connector for the ground lead and a 3/16" connector for the brake light positive lead. I assume these are used if you need to tap into the brake light circuit while towing the vehicle. I used the 1/4" connector for the ground lead to the backup sensor. I modified a standard automotive connector by soldering a 5/8" length of a 4-40 brass screw where you would normally crimp the wire. I cut off one of the locating pins near the backup light. I drilled a hole through the plastic carrier and ran a 4-40 tap through the hole in the plastic and the existing hole in the positive backup light trace. I used a 4-40 nut on both sides of the plastic carrier with a flat washer and lock washer on the trace side. The photo shows the blue insulation on the connector, but, I had to remove this since it shrunk when I soldered the brass screw in place. I replaced the blue plastic insulation with a short length of clear flexible tubing.
>Charlie
05-21-2018, 03:43 AM
#11
Just a quick follow up; I did this modification today, and all worked well. I used a 1/2" long, 4/40 bolt and a crimp connect eyelet with an internal diameter of 3mm. Everything worked very well, and the result is far more professional looking than kludging around with the wiring harness. I'm really grateful for the information.
>Charlie
>Charlie
