After driving through a downpour, my headlights wouldn’t turn off. I pulled the fuse, and when I put it in again, the passenger side headlight wouldn’t turn on- checked the bulb, it’s ok, amateur mechanic from the hood tried to ground a wire, nothing. I read that the schematics for the headlight wiring are odd in this car. Looking for a solution my mechanic in the hood could try before going elsewhere. 
The wiring for the headlights on this car are pretty straight forward, but I need a little more information.
This car has daylight running lights (DRL). This will be on anytime the engine is on, headlight switch is off and the parking brake released. That will be the highbeams, but at a low voltage so they are dim. They should go off when you pull up on the parking brake handle.
Were the high beams on or the low beams? Will the passenger side headlight work on high beam or low beam? Does the DRL work?
The DRLs work. The low beams were on when the problem happened (they wouldn’t turn off). Just checked, and the right side high beam is very dim. The right side headlight itself does not come on at all.
If it all started when it was wet out, first thing I’d check is the relays under the hood. Might have gotten stuck on. Usually there are others in the same bank with the same part numbers so you can just swap them to see what happens. New ones are only about $10. Then I’d be looking for ground or connector problems.
The common denominator here is the DRL relay, it controls the right side headlight, both high and low beams as well as the DRL mode.
On second thought, look at the right headlamp fuse in the under hood block.
When you pulled a fuse, which one did you pull? In the under hood fuse block, there is a fuse for each side.
The DRL relay could be causing the current problem, or it could be the right headlamp fuse, but neither caused the original problem. The water from the downpour must have shorted something out, providing a ground for the head lights.
In this headlight system, as with most systems, the head lights are hot all the time. When you turn on the switch, you provide the ground so that current can flow through the headlights. The DRL relay provides a ground when the headlights are off, but the ground is for the high beams in series, so each bulb only gets 6v instead of 12v they get when the ground is provided to the high beams in parallel.
The Body Control Module is involved in this circuit somehow, but I think it is for monitoring only. If you can find someone with a code reader, you may get a code starting with a B or U instead of a P. These do not trip the check engine light and maybe stored only in the history section, so you may need a higher end scan tool and not just a simple code reader. If you get a code, post back and I will tell you what it is saying.
Took another look at the wiring. The body control module provides the ground to energize the DRL relay. It also provides the indicator lights on the dash. Other than that, it is how I described above.
When energized, the DRL relay takes the ground side of the left head light bulb and connects it to the ground side of the right high beam bulb and it takes the hot side of the right high beam bulb and grounds it. That puts the two high beam bulbs in series, so they each get 6v instead of 12v
When de-energized, the DRL relay provides 12v to the right side high beam bulb. The light switch in the multi function stalk provides ground to both high beam bulbs when it is on and in the high beam position. It provides ground to the low beam bulbs when on and in the low beam position.
The DRL has nothing to do with the low beam bulbs so if the right side low beam is out, then either
the right headlamp fuse is blown,
the bulb is bad
or the splice that provides 12v to both right side bulbs is bad
or the splice that splits the ground wire to both low beam bulbs is bad.
The splices are in the bundle under the under hood fuse block. Maybe the whole thing will work when it all dries out.
Appreciate all the advice; not sure which fuse I pulled to get the lights to turn off, and this happened a few months back, so it definitely has had time to dry out I’ll take what you all have said to my mechanic to try to help him figure it out. Thanks again!
Before you go to the mechanic, save yourself some money by either fixing this yourself or providing more information to save the mechanic some time.
First check the DRLs. Are they bright enough. They should be bright enough to see in daylight. If they are, that rules out part of the DRL relay. If they are very dim, then that would Make the DRL the most likely culprit.
Now open the hood. You will find the underhood fuse block, also known as the Fuse and Relay panel at the front of the engine compartment, drivers side, between the battery and the fender. It has a knob in the center that you use to unscrew it. When you take the cover off, turn it over and you can see the map of the fuse and relay layout.
The headlamp fuses are at the front of the fuse block on the left (passenger side, left as viewed standing in front of the car) front corner, second column from the left. The first two fuses are the headlamp fuses, the passenger side (R HEAD) headlamp fuse is the one closest to the front, the drivers side behind it.
It is possible that when the R HEAD fuse was pulled, it got some junk in the fuse block or on the fuse spades. Just pulling out the fuse and brushing off any junk, reinserting it might fix the problem. It is also possible that when the fuse was reinserted, that the receptacle side in the block got pushed in and you are not making contact. If that happened, you may need a mechanic to fix it. Lifting that block out to get behind it is not easy. You might swap the first and second fuses to see if the problem switches sides. If it does, you will also loose your DRLs.
The DRL relay is the only relay not in the right most column, next to the fender. It is near the top of the block above the headlight fuses. If the DRLs are dim, you might remove and reinsert it just to refresh the contact with the spade connectors.
BTW, I have a 2002 SL with 238k miles on it. It has been one of the most reliable cars I have ever owned, and that includes a slew of Japanese cars.
Sweet, mine only has 74K so far…I will check out the fuse stuff tomorrow-the DRLs aren’t dim, the passenger side high beam is very dim when I turn the highbeams on (maybe it just looks very dim compared to the highbeam that’s on) and the passenger headlight remains off thru it all I never realized the DRLs turn off when the emergency brake is on before. Appreciate you sticking with it to help me out…I’ll let you know how the fuse thing works out, Stef
I have the factory service manuals too, so anytime you need a little help, post here and I will do what I can.
HA! I put the spare fuse in the left headlight spot, and now all the lights work-high, low, everything. Wow. Guess I had myself convinced it was a wire problem!
Here are the schematics.