Wiring question - Lucas rectangle tail lamps and Ron Francis harness

[Gumball]

I've heard that there is a need to use a trailer light converter when using the Lucas rectangle tail lamps (which have only a single twin-filament bulb), but I'm struggling to understand why that would be necessary with the Ron Francis harness. I can understand the need if using a donor Mustang wiring harness and computer, though.

From what I can tell, the Ron Francis harness is designed to hook to the standard FFR four-light system as follows:

1) One lamp per side with a single filament bulb with each serving only as a running light - i.e., tail light feed;
2) One lamp per side with a twin-filament bulb with each serving three functions - i.e., tail light feed, turn signal feed, and brake feed.

NOTE - all would receive a ground.

It would seem that the Lucas rectangle lamp acts in place of #2, while #1 is, for lack of a better term, omitted.

My Lucas lamps have two wires each - a yellow that activates the running light (dim) filament and a green one that activates the stop/turn light (bright) filament. So, I'm wondering if I can simply connect the running light feed to the yellow and the stop/turn feeds (respective for each side) to the green - plus a ground to the housing.

Thoughts?

[Mark Dougherty]

Hi Chris
The RF harness is a 4 wire tail light system. 2 lights per side of car.
1 ground for both lights
2 running light to both lights
3 turn signal to 1 light
4 brake to second light

When going to a 2 light system 1 per side of car.
You will only use wires 1,2 and 3 you will not use the brake wire.

Install the rectangular lights using 1-3
#1 ground going to the stud holding the light to the body
Then install a 3 wire to 2 wire trailer brake converter under the dash.
. This will combine the brake wire and the turn signal wire into one

[Mark Dougherty]

Double post

[SCFFR]

Hey Chris,

Ran into the same issue on my MkIV. Like you, using the rectangular tail light (got mine from **********) and the Ron Francis harness. You are right that the harness is made for a dual tail lights per side and as you stated the rectangular light has a single bulb with two filaments.

I found the answer from one of the members on the "other" forum who was extremely helpful. He provided a detailed schematic and parts list for the relays needed to make this work. However, instead of trying to make my own, I found a turn signal module from Watson's Streetworks for about $65 that was wired and ready to install. On the attached pic, it's the small green circuit board with the black relays. All of the wires are already soldered, the wires are color coded and comes with easy to follow instructions. I used the Russ Thompson turn signal assembly which was easy to wire to the module.

Also note that I had installed a small fuse box. The module needs a 3-5 amp fuse so I added the box in case I need to add an extra circuit for something later.

Very easy to wire and works great.

Ron
26765

[Gumball]

Ron,

How does that set-up differ from what Mark is describing - or is it one-and-the-same?

[SCFFR]

Hey Chris,

To be honest, when I posted about my taillight issue, I don't recall anyone responding about using a trailer connector so I really don't know. The module I used has a set of relays that keeps the opposite brake light on when the other side signal is flashing. Sounds like the trailer connector works the same and is probably cheaper. I would give it a try first.

Ron

[Mark Dougherty]

yes the street works does the same thing.
but the trailer converter is under 10 dollars on amazon.
and also no fuse needed.

[Gumball]

I've been plugging along on my wiring for the past few weeks, connecting circuits and verifying that things work. I've played around a little with the dash wiring and, as part of that process, I've installed all the gauges and switches in the dash (out of the car). I also did a little "wire dieting" on the dash harness that came from Ron Francis since I'm using the mechanical Smiths gauges and quite a few of the feeds in the harness are not necessary. I still have quite a bit to do on that part before I can call it done, so in the mean time I've been focusing on getting all the other chassis circuits working.

One of the stumbling blocks was my use of the rectangular Lucas tail lights with a single two-filament (1157) bulb. The Ron Francis harness and the Russ Thompson turn signal switch are not designed to do double duty with the Mustang brake switch, so I found that I would either need to incorporate a 3-into-2 trailer wiring converter or a relay system in order to make those lights work; i.e., for the bright filament on the bulbs work as both brake lights and turn signals... including at the same time. Well, faced with added wiring complexity, more things to fail down the road due to heat and vibration, or simpler wiring with more lighting power, I, like electricity, went for the path of least resistance.

Here are my modified tail lamp housings I made previously and that now include two sockets per side, using the butchered original rear lamps from FFR. Those original lamps are just chrome plated brass and cut easily with tin snips. I fab'd up a divider for the housings so that the brake and turn signal lights wouldn't bleed into the other side, too. After drilling a few additional holes in the housings, including a couple of 1 1/8" holes in each for the light sockets, I riveted the sockets and divider in place using some clear seam sealant to weatherproof the housings a bit.

http://i845.photobucket.com/albums/ab15/CCRsAC/IMG_20140318_083222362_zpsc34b9335.jpg (http://s845.photobucket.com/user/CCRsAC/media/IMG_20140318_083222362_zpsc34b9335.jpg.html)

Here are the housings with the sockets and bulbs in place - but just held together with clecos before I buttoned them all up:

http://i845.photobucket.com/albums/ab15/CCRsAC/IMG_20140316_155048396_zps99dd5a6b.jpg (http://s845.photobucket.com/user/CCRsAC/media/IMG_20140316_155048396_zps99dd5a6b.jpg.html)

I also had to remove the lower portion of the Lucas lights that holds the socket in place in those, so now the entire lens is open so that both the top and bottom lights in the housing will shine through. Admittedly, the lower bulbs are shining through the reflector portion of the red lens, but they're still pretty bright.

Now, I'll wire the tail lamps just like they would have been if I'd used the four round lights in the first place, except that I'm only going to use the top bulbs for running/park lamps. The top bulbs will handle the brake function while the lower bulbs will separately handle the turn signals. Now, when I hit the brakes and then turn on a turn signal, I'll have two bright lights on solid and one bright light flashing. More lights - less complexity! I could also have the lower bulbs be on as running lights, but I like the vintage look of those only in the top - we'll see, though, I may decide to hook those up, too.

With the housings made previously - see the post in the Mods for Originality Forum for details and PM me if you'd like a copy of the template - this was a very easy additional mod and will make a good bit of difference in safety by offering more candlepower at the back of the car.

[Gumball]

Wrong thread.