LED License Plate & Check Bulb Relay Bypass Mod w/Pix

[everwild]

Note: Car is a 1988 528e.

So I decided to upgrade my license plate, trunk and interior dome lights to LEDs. In this write-up, I will only cover the license plate LEDs mod, since it's the only one out of those three that triggers the check bulb relay. Swapping out the original bulbs with LEDs is straightforward, but bypassing the check bulb relay is a bit more complex. Bypassing the check bulb relay eliminates the need for load resistors. Well, here we go!

Tools you'll need:
A few screwdrivers, soldering gun, solder, flux, cutting pliers, tweezers and a paper clip.



Unscrew the four screws holding the two plate light covers...



Take out the covers by pulling and slightly wiggling them...



Disconnect the wires...



New LEDs. These are by Pilot, #6461. I got them at my local Walmart...



While you're at it, I recommend upgrading the license plate light covers to "Hella" ones. They are much clearer and look nicer! Plus, the new rubber gaskets/grommets that come with them are definitely worth it! I got mine off of autohausaz.com, part #10123813-63261354665. Note on autohausaz web page, "Please note, original left and right versions were superceded a number of years ago by one version to use for both. 2 per car."



LEDs in place...



Looks MUCH better and brighter than the stock bulbs! Easy part done, now the check bulb relay...






You can install the LEDs and be done with it, but the license plate check light will always be on as so. If this bothers you, continue reading...



Using a flat head screwdriver, remove the three retainers holding the center trunk cover panel...



Remove the panel. You will see the check bulb relay (circled white) on the left side...



Remove these two screws holding down the check bulb relay...



Once you remove the screws, unplug the two connectors. There is a dark brown cover on the back side of the relay (white square). You will have to use a small flat head screwdriver to pry it open...



Once you remove the back cover, push on the pins with your fingers to remove the actual relay from the housing...



This is how the top of the relay looks like...



These are the two pins (red arrows) on the back side that you will jumper together using a paperclip. Take your cutting pliers and cut a short length of the paperclip, just enough to reach both of those pins. Using your tweezers, hold the small paperclip rod in place while soldering it to both pins...



This is how it should look like when done (circled white). Dip a spare toothbrush in some acetone and clean/brush off the excess flux. Install everything in reverse order using common sense...



No more license plate check light! Hope this was helpful, enjoy your day everyone!

[Shawn D.]

Nice writeup!

[sunnyrollins]

Dude, thank you! I have this issue, have higher priority issues to fix, but need to get this done on the horizon shortly. Thanks again.

[russellrh72]

My brake light and license plate light check bulbs light up about every fifth time I drive my car. They all work fine but the lights come on every now and then. I have changed the relay and it still happens. Would this procedure keep those from coming on? Brake light check as well?

[everwild]

My brake light and license plate light check bulbs light up about every fifth time I drive my car. They all work fine but the lights come on every now and then. I have changed the relay and it still happens. Would this procedure keep those from coming on? Brake light check as well?

I truly don't know. If you installed a brand new relay but the problem persists, then there is something else causing it, so if you do this procedure and jumper the pins on the relay, the thing causing the problem might still trigger the bulb warning. But you could always try it out. Also, this procedure only covers the license plate LEDs, not the brake lights.

[pennybond]

Thanks for the great write up.

I'm doin' this on the E23 and E28! That check relay has been driving me nuts every time I turn on the headlights.

[VW+bimmer=bliss]

The reed switches inside the coils are held open because the current flowing through the coil turns it into an electromagnet, holding the switch open. When the current flow decreases enough or stops all together, the reed switch closes, signalling the bulb is out and turns on the 'check' light in the overhead display. If the check light keeps coming on for the bulbs check your grounds for cleanliness and tightness and also the bulb sockets as well. Check trunk lid gasket and sunroof gasket/ drains for leaking if your car sits outside.
I personally do not mind the load resistors, but this is a nice alternative to them. Good information by OP.

[four2zerohero]

Awesome, great contribution

[John in VA]

Great job on the relay.
All the new-car guys are interested in making it easier for the LEOs to see their rear tags with LEDs - I don't get it. Bright reverse lights do make sense.

[M3 Cereal]

Sorry to revive a dead thread, but I was able to follow this guide to this point without photos, which of these do I solder together? Thanks

[Galahad]

@M3 Cereal: Could you post a photo of the back side of the board? That would make it easier to show you what to do.
If you're trying to patch out the license light, you need to solder a wire between the "KKL" input pin and the resistor attached to pin 31 (on the far side, not pin 31 directly).

[M3 Cereal]

Thanks for the reply, I put it back in the car last night but haven't screwed it in.

I will post the pic of the backside today.

This is how I wired it though, I found a random pic on google that looked like they were doing the same thing, so I tried this.

I’ll test it when it’s done raining.

Unless someone sees that it’s completely wrong.
I drove the car last night seemed fine, but I have the check panel unplugged cause of the license plate light

[Galahad]

I took a photo of one of mine and poked through the ETM. I labeled the pins used for the check functions, and highlighted what I think is the easiest way to patch out each of the three systems the relay checks.

M3 Cereal it looks like what you have disables the "Brakes" warning. I don't know if that's the one you were aiming for, but I hope this is helpful either way.

[M3 Cereal]

This is a great help, can you repost your picture with a link? It didn’t post your image in the thread.

[demetk]

I bypassed all like this:

[Galahad]

This is a great help, can you repost your picture with a link? It didn’t post your image in the thread.

Fixed it. I keep trying to get google photos to work properly - I should probably give up and switch to some other hosting service.

[Oz77]

Is there a problem with jumpers at the C2 connector
54KL <--> 31 Stop lights (might need a resistor)
KKL <--> 31 License plate
58KL <--> 31 Tail lights
Ideally a working rear light check relay could be setup up with another set of reed relays with the correct pull in level adjusted for LEDs