92 sc300/soarer, Hello, I removed the high mount 3rd brake light, Installed OEM 94 sc400 spoiler. found connector in trunk, brake light in spoiler works good. all lights good. Now I get light fail warning on dash. I'm thinking it has something to do with the disconnecting of the connector on the removed high mount 3rd light.... Question is there something you install at high mount connector or ?. Power is still at high mount connector.

 

There's a different lamp failure module for spoiler vs parcel shelf brake lights. It's in the trunk, clipped to the back side of the brace that the antenna is behind. Little plastic box with a single connector.

 

My 1993 SC300 was a factory wing-less model that came with the high mount 3rd brake light. I later installed a whole trunk lid with factory LED flat spoiler from a 1992-1996 SC400. I left the 3rd brake light installed and connected. Mostly I did this because I figured you cannot have too much brake light visibility with all the unnecessarily tall crossovers and SUVs on the roads today.

I think the issue may be that you need to complete the circuit where the 3rd brake light was either by making a pigtail connector with a loop or by reinstalling the 3rd brake light. What is happening is that the SC's brake light failure ECU (yes, there's a separate simple ECU just for this purpose) is reacting to the change in resistance (I think) that it is detecting in the circuit with the absence of those conventional bulbs housed in the 3rd brake light assembly.

Also I'm not 100% certain on this but I *think* sometime in the middle or late 1990's the FMVSS changed and required a "high" mount 3rd brake light on all cars even if they came with an additional spoiler or wing with a brake light embedded. It would therefore not be legally required to keep the 3rd brake light in your 1992 SC300 since your car pre-dates the change in Federal rules... but... it also can't hurt to keep it installed in addition to the spoiler if you want to. And it would be an easy way to eliminate the tail lamp failure lamp being on.

Either do that or completing the circuit with a pigtail connector you make would probably solve it (someone please correct me if I am wrong!). However just in case you ever need to reinstall that 3rd brake light I highly recommend getting a soldering gun, some heat shrink tubing and a set of small generic connectors to make a little detachable sub-harness out of your original 3rd brake light connector to make a circuit completing loop. That way you can always put it back to stock if necessary.

Again... someone correct me if I am wrong but unless you reinstall the 3rd brake light assembly I think the way to get the tail lamp failure ECU to be happy again is to simply complete the circuit again in that location.

t2d2, does that alternative solution sound correct to you? And did I understand you correctly that there are actually two tail lamp failure detection ECUs? One for all the standard lights and one more for spoiler equipped models? Or have I misunderstood?

 

I've never tried running both 3rd brake lights simultaneously, so I'm not sure what that does to the circuitry. My guess is, as long as the lamp failure module in the trunk sees the resistance it's looking for from either source, it's happy. I don't know if that's considered the ECU, or if there's another one downstream it reports to?

But yeah, there are different versions of the lamp failure module for each year (range) SC. One for spoiler, one for parcel shelf. Same connector for either, so super simple to swap out for the desired one. (Edit: No need to complete the circuit on the unused one, be it parcel shelf or spoiler.)

 

Interesting! So the OP's issue seems to have to do with the later model spoiler not being fully compatible with the spoiler lamp failure module his 1992 SC already came with?

For what it is worth I left my SC300's factory 3rd brake light alone when I installed the 1992-1996 style SC400 factory spoiler I used. I have no idea which of those model years the spoiler came from but I have never once had an issue with my tail lamp failure module as a result of installing it.

 

Thanks, I'll check that out

 

Yep, installing the lamp failure module from a '94 SC400 should do the trick. (Probably any '92-94 SC400 one will work, but I'm not sure offhand which years are identical and whether it follows the tail light generations.)