SL/R129: DRL foglights
01-20-2016, 08:46 AM
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500sl
DRL foglights
Hello from Brussels.
I bought a '91 500SL a few months ago.
As I already did on my BMW 850ci, I would like to add DRL on my SL.
The plan is to use the existing foglights as DRL. When the ignition is turned on, they should go on. As soon as the parking lights are turned on, they should automatically switch off again. This can be realized by using a simple small NC relay (see my diagram in attachment).
As I have no wiring diagrams of the R129, I would appreciate your help to locate the three interconnection points (marked on my diagram) needed for my mod.
1) Wire which is getting 12V when the parking lights are switched on (to supply my relay)
2) Ignition “15” wire (which will supply the foglight in DRL mode through the NC relay contact)
3) Wire which is leading to the front foglights
In my BMW 850ci I managed to find these three interconnection points in the area below the steering wheel. I want to avoid to mess around in the engine compartment. So I hope this is also possible in my SL.
Looking forward to hear from you! Thanks a lot.
I bought a '91 500SL a few months ago.
As I already did on my BMW 850ci, I would like to add DRL on my SL.
The plan is to use the existing foglights as DRL. When the ignition is turned on, they should go on. As soon as the parking lights are turned on, they should automatically switch off again. This can be realized by using a simple small NC relay (see my diagram in attachment).
As I have no wiring diagrams of the R129, I would appreciate your help to locate the three interconnection points (marked on my diagram) needed for my mod.
1) Wire which is getting 12V when the parking lights are switched on (to supply my relay)
2) Ignition “15” wire (which will supply the foglight in DRL mode through the NC relay contact)
3) Wire which is leading to the front foglights
In my BMW 850ci I managed to find these three interconnection points in the area below the steering wheel. I want to avoid to mess around in the engine compartment. So I hope this is also possible in my SL.
Looking forward to hear from you! Thanks a lot.
Last edited by marc123; 01-20-2016 at 08:53 AM.
01-22-2016, 02:01 PM
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1998 SL500
Here is a section of the exterior lighting wiring diagram for your '91 '500 showing the fog light wiring:
E5/1 and E5/2 are the fog lights, the +12V wire colors are gray/green/white and gray/green.
N7 is the lighting control/lamp failure monitoring module. Disconnecting the fog lamps from N7 will cause it to believe the lamps are burned out.
To prevent this some similar load would have to be substituted. However as the lamps are 55W each presumably the substitute load would presumably have to also draw 55W (4.6 A) to keep N7 happy.
Two 100 W rated resistors of 2.7 Ω each would do this, however they would also generate 55 W of heat in the process--not an inconsiderable amount (wrap your hand around a 60 W light bulb).
They would look like this and cost $10 each or so:
It could be that higher value resistors, resulting in less heat, would make N7 happy--IDK you will have to experiment...
E5/1 and E5/2 are the fog lights, the +12V wire colors are gray/green/white and gray/green.
N7 is the lighting control/lamp failure monitoring module. Disconnecting the fog lamps from N7 will cause it to believe the lamps are burned out.
To prevent this some similar load would have to be substituted. However as the lamps are 55W each presumably the substitute load would presumably have to also draw 55W (4.6 A) to keep N7 happy.
Two 100 W rated resistors of 2.7 Ω each would do this, however they would also generate 55 W of heat in the process--not an inconsiderable amount (wrap your hand around a 60 W light bulb).
They would look like this and cost $10 each or so:
It could be that higher value resistors, resulting in less heat, would make N7 happy--IDK you will have to experiment...
01-22-2016, 04:27 PM
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Thanks for your quick reply!
Maybe my previous message wasn’t clear enough, but I don’t want to disconnect the foglights. The idea is to leave the existing wires in place, the foglights should also keep their original function as foglights!
On your wiring diagram I noticed that each foglight has a separate supply, this means that I would need to install two relays, one for each foglight. See my new wiring diagram in attachment.
Questions:
Do you know where this lighting module N7 is located in the car ?
Do you have the complete wiring diagram of that N7 module ? I would like to check if there is also an "15 ignition-", a "parking light 12V-" and a "ground" -wire available in that area. This would be ideal as I would have everything needed to hook up my relays and realise the DRL’s.
All help is really appreciated!
Maybe my previous message wasn’t clear enough, but I don’t want to disconnect the foglights. The idea is to leave the existing wires in place, the foglights should also keep their original function as foglights!
On your wiring diagram I noticed that each foglight has a separate supply, this means that I would need to install two relays, one for each foglight. See my new wiring diagram in attachment.
Questions:
Do you know where this lighting module N7 is located in the car ?
Do you have the complete wiring diagram of that N7 module ? I would like to check if there is also an "15 ignition-", a "parking light 12V-" and a "ground" -wire available in that area. This would be ideal as I would have everything needed to hook up my relays and realise the DRL’s.
All help is really appreciated!
Last edited by marc123; 01-22-2016 at 04:29 PM.
