How-To: Installing 300C Tail Lights on a Touring/Base

[italianguy63]

Read this entire post carefully, and beware there is a possible danger in doing this mod. I will take no responsibility if damage occurs or if this would void your warranty, etc. etc. etc. This post is for information purposes only. Proceed at your own risk.

There is a lot of ideas we (Mr. Incredible and myself) tried. Many were unsuccessful. I will spare you the details in this post to keep it short. PM us if you want to know more!

Look at the attached pictures, and be sure you are comfortable with this before starting.

Release the FCM/IPM from the fender by releasing the 3 clips.

The right rear blinker is controlled from plug C1 of the Integrated Power Module at pin 17. That wire is WT/YEL and goes back to the rear lamp.

Cut the WT/YEL wire on C1 and splice it into plug C2 of the FCM at pin 8. That wire is WT/TN. This signal controls the right front blinker.

Similarly, the left rear blinker is controlled from plug C3 of the Integrated Power Module at pin 3. That wire is WT/DG and goes back to the rear lamp.

Again, cut the WT/DG wire on C3 and splice it into the plug C2 of the FCM at pin 10. That wire is WT/LG. This signal controls the left front blinker.

This puts the rear blinkers in parallel with the front blinkers and will bypass the "brake light" signal sent to the rear (Touring) lamps via the Touring FCM firmware/software.

I left the original outputs “open” and the FCM realizes there is a (open) fault with the (now missing) rear turn signals. A "fast flash" scenario occurs, so dummy loads (ballasts or resistors) will need to be added to the two unattached leads and tied to ground to fool the FCM. I plan to do this later. This arrangement would be the same as if you put LED bulbs in. Attach the two hanging leads from C1 and C3 to ballasts or resistors and then the other end to ground. That will fix the "fast flash" issue.

Important notes:

Disconnect the battery and wait 10 minutes before messing with the FCM. It is static sensitive, and quite expensive if you zap it. Use proper anti-static procedures while doing this!

Be careful with the plugs—they are somewhat complex to take off. C2 is removed by sliding the red “keeper” towards the base then squeezing the plug near the wires.

C1 and C3 are removed by sliding the keeper, then pulling the “lever” type lock away from the plug (it pivots), then squeeze the plug near the wires. Reattach the plugs in reverse order.

Use solder, heat-shrink, and black tape to re-wrap everything to keep the install tidy. Take your time and do it right!

The WT/YEL wire on C1 is easy to locate. It is in the corner of the plug. See pic.

The WT/DG wire on C3 is tricky. There are 3 wires with green next to each other at the top of the plug. The WT/DG one is the “middle” one. Be sure to identify it before cutting!

The wires on C2 are on the bottom of the plug (and next to each other). Refer to the diagrams I have copied for you, and make sure you have the right wires before you cut!

Leave about 2” of wire on the plugs to allow you to attach ballasts. You are splicing the “harness side” part of the wires into the wires on plug C2. I had to add extra length to these wires.

Finally, use the “C” tail-lights (with the “C” harnesses) plugged right into the stock connector at the back. This mod takes advantage of unused wires in the harnesses that the “Touring” does not use. DO NOT use the “Touring” harness. The aftermarket lights (like the Sonar LED tails) already have an electrically equivalent harness to a stock “C” light.

Cheers!

Italianguy63 and Mr. Incredible

[italianguy63]

Thanks to you all-- you are too kind really!!

Thanks for all the help Marc! (Mr. Incredible)-- you truely are incredible. If you guys knew some of the technical ideas we were throwing back and forth.. it was amazing. It is too bad the ultimate solution ended up being kind of a "brute force" answer. But hey, it worked right?!

I re-edited the original post to make some points slightly more understandable. Such as the resistors/ballasts-- I don't have them on right now, but will do this later... I know adding them will stop the "fast flash," but it doesn't really hurt anything.

I also took a before/after picture... and I added a couple more here because I could only use 5 on the original post.

I know some think the silver is "ricey"-- but I like the silver on silver all the way around.

MC

[italianguy63]

Update: I picked up an item that should be a perfect fix for the "fast flash" situation. It came in yesterday, and I will try to get it installed today with a picture or two. It looks perfect! It is 2 load resistors all in an epoxy filled black aluminum heatsink. It can mount with double sided tape and has 3 wires coming from it (one for each turn signal, and one wire to go to ground). It looks nice and is small. Cost was $18. The part I got is called a "dual-load equalizer" made by SDC (Signal Dynamics Corp.) Part# 340-300.

[italianguy63]

OK-- I am happy to report this is the perfect solution to the "fast flash" problem.

Connect one of the "equalizer" wires to each of the short pieces of wire you left coming out of the ICM plugs (see pic).. again use solder and heatshrink (note the red heatshrink in the pic).

Connect the 3rd wire (black) to ground. The shiny FCM case looked like a great candidate! So I soldered (and crimped) a lug onto the black wire-- and put it under the bottom left screw holding the FCM to the ICM. The wire lengths are perfect as is.

I just double sided taped (supplied) the SDC equalizer to the mount for the FCM/ICM on the left side (see pic). It is pretty hidden from sight and barely fits.

VIOLA!!

That's two projects done before noon!!!

MC

[italianguy63]

The brake lights on the "C" are on their own circuit (different wire from the Touring/Base); the brake lights on the Touring/Base are on a different wire that combines the brake function with the turn signals.

You can use the "C" harness to make the brake lights work alone, but you lose the function of the turn signals. If you use the stock harness without isolating the brake/turn signal... the turn signals come on when you hit the brakes.

The point is not "how many" bulbs are involved. The problem is which wires the bulbs are connected to.

The Forward Control Module (FCM) controls the functions of the lights-- and we found no way to change the "software/firmware" involved. Hence, the purpose of this thread-- you need to do a little rewiring at the FCM to fool it to make the lights work right.

MC