LED conversion -- highs, lows, and relay swapping

[Jack Olsen]

There's not all that compelling a set of reasons to switch to LED bulbs for any part of the 911 except the dash, in my opinion. There's a slight safety argument for the faster brake light response, I guess. But the problems with the directional nature of most LED bulbs means you're sometimes trading the safety of the fast response time for the danger of less-visible brake lights.

In my case, there was another factor. I wanted to cut weight to the back of the car, and I found a way to put together an LED setup that was lighter than my 911R-style lightweight tail lights. This also let me change the look of the rear of my car back to something closer to stock.

Before:



After:



But the trick to saving weight back there doesn't have anything to do with the bulbs you run, it's that big heavy 4+-lb box that protects the bulbs from the weather. My solution to that was to get an LED setup made for a submersible boat trailer, which allowed me to put together a very light box without having to be concerned with water intrusion.

Heavy:



Light:



Here's the inside:



As an added bonus, the multiple array of bulbs in the trailer setup eliminated the normal problem with LED bulbs, in that there are so many sources of light that you don't suffer from the directional issue.

Okay, all good so far, right?

Well, no. The problem with going to LED turn indicators is that you have to switch to an electronic flasher relay (made for LEDs) and have LED bulbs in front as well as in back. With no LED bulbs on hand for the front, I had to go with a very inelegant solution -- I soldered together a pair of incandescent replacements to piggy-back on top of the LED bulbs for the turn indicators, which I disabled.



So I was running incandescents all around for turn signals, but LEDs for running and brake lights in the back.

After a couple of weeks, the flasher relay and bulbs arrived. The first thing I did was to test the new bulbs in front. The seller promised a warm white bulb that would alternate with an amber front turn flasher.



As a reference, here's the incandescent front bulb:



So I ordered another set of LED bulbs -- this time with two arrays of amber light elements. They finally got here, but were significantly dimmer than the incandescents they were replacing. The camera doesn't show as much difference as there was in real life.



Still, they worked well enough that I thought I could finall drop in the electronic flasher relay and solder up the rear LED indicator lights.

Am I the only one who has the gas vapor cannister basically sitting on the flasher relay up under the dash? It clearly calls for a small monkey with long arms to make the switch, and there was a lot of German cursing done before I finally got the new relay in place.

Then I soldered in the LED sets and tested it out.

Crap.

Good grounds all around. Pretty fresh contacts for all the bulb connections. But suddenly I was getting the left rear indicator flashing at half strength when the right indicator was turned on and flashing. And the reverse was also true -- whichever side was not being signaled would blink along at half strength, but only in back.

I checked my grounds again, confirmed my wiring. Scratched my head. Cursed some more.

Couldn't figure it out.

So after cooling down a little, I decided to go back to incandescents for turn indicator lights. It just wasn't a big enough deal to lose more time over. So the first thing was going to be the tough part -- switching back to the incandescent flasher relay. More cursing. Scuffed knuckles. But finally, I got it in.

Then I put the incandescents back in front, and decided -- before getting out the soldering iron again -- to turn on the signals and see what the 'fast flashing' condition was like.

I didn't get it.

With incandescents in front, and the LEDs in back, everything worked perfectly. The dash indicators worked. There was no half-bright condition anywhere. Worked with running lights on. Worked with brake lights on.

It just worked.

So, I've left it that way. Maybe someone can explain how the incandescent flasher is getting the correct resistance from only two incandescent bulbs. Or maybe someone can steer me straight if there's some hazard to running things this way. But outside of that, I'm going to stick with this new arrangement.

Here you can see how the array of bulbs widens the visibility of the rear lights.

[otto in norway]

Interesting Jack.
I'm in the middle of almost exactly same project as you are.

First to your question regarding the flashing circuit. You think you are onto something with the resistance. I have not seen the schematics for the flasher, but from what I too understand, it needs a certain resistance in the bulb(s) in order to work as intended.

Good to know that one bulb in front will do the trick.
You see, I too want to shed some weight. So I just cut out unwanted material from the original rear housings, and fitted new inside/ back wall with the help of epoxy fiber, polyester, and plastic back plate.
Now I am in the process of mounting some LED "sheets" on the back wall inside. The preliminary tests are looking promising.

Some pics to show what I mean:

First cut (Not pretty, but a few more precision cuts later not too bad)


LED sheet:

[tirwin]

Jack,

I'm curious about this as well. I added the Hella LED TBL for added visibility and it is well worth it, but that is just augmenting the incandescents. I have a friend who did the LED conversion on his Datsun 260Z and he had a similar problem with the resistance. In my opinion, he also lost some visibility in the bright sun. The LEDs tend to work well at night but in the daytime they can be less visible. I think this is because of the directionality and you gets less reflected light from inside the housing. Still, you've got quite an array of LEDs there!

As far as the flasher relay... The way I understand it, when you switch to LEDs there is a minimum load that is required for the turn signal relay to work. If you go with all LEDs, the lower load isn't enough to trigger the relay, so that's why you need one designed to work with LEDs. By just replacing some of the incandescent bulbs instead of all of them you probably have enough load still to trigger the relay. I think a concern might be that if an incandescent bulb failed, would you lose all your turn signal function? Or if you replace an incandescent in the future with a more efficient bulb, might you fall below the threshold where the relay won't work?

[TOO RUF]

My suggestion is to figure out a way to use vintage lenses or the ones you had. The new lenses don't fit the look of your beautiful 911.

[Fishcop]

Jack, a lot of the aftermarket trailer lighting systems are designed to 'expect' that the tow car isn't set up for them. In the circuitry you probably find that the manufacturer has included a resistor to make the flasher think its flashing incandecent bulbs... When you combine the resistor in the light array and the LED specific flasher, perhaps there too much resistance leading to "inconsistencies" such as dimness?

I personally like the more stock looking lights on your car... As you know, I had the 911R lights for a while too, but they do seem a little odd on a fat RSR rear

[quattrorunner]

That's cool, I've been putting together a list of parts to do a similar thing. But for me I want more quality light is the reason. New lenses might be all I need.

[ischmitz]

Jack,

a flasher relay requires a certain minimum amount of current to be drawn to work properly. Modern LED are not nearly drawing as much current as an incandescent light bulbs. In the old days a flasher relay was a bi-metal strip with some wire wound around it acting as a switch: When the lights came on the wire would heat up and the strip bent. the circuit opens, the strip cools and bents back to closes the contact. If one of the two flasher bulbs was out the frequency nearly doubled and the working flasher light goes very fast......

That is why others suggest to add a beefy resistor in parallel with the LED. Try something like a 100 Ohm and make sure the resistor is able to handle the current. Maybe start with a 2 Watt version and see if it can take the heat. The math is (14.4/100)*14.4 = 1.96 Watt. Since the duty cycle is about 50% the resistor will dissipate about 1 Watt.

Ingo

[Jack Olsen]

Otto, that's a cool project. I've been thinking about doing something like that with the front buckets. They've gotten so expensive though, that I'm a little cautious about cutting a set up.

Maybe another aluminum box for me?

John, I think you're correct about why the LED lights are working with the old-style flasher -- and why they didn't work with the LED (electronic) flasher. Each LED is paired with a resistor on the board. In this picture, you can see how the whole board is sealed in clear plastic to keep water out.

The part that doesn't makes sense about including the resistance is that a car or truck using the trailer is still using all of its existing bulbs, whether they're incandescent or LED. This would make me think you wouldn't need to worry about adding resistors, since if the car has an electronic flasher relay and LED bulbs, the resistance might cause problems for it.

Originally Posted by TOO RUF

My suggestion is to figure out a way to use vintage lenses or the ones you had. The new lenses don't fit the look of your beautiful 911.

Here's an actual 2.8 RSR:



It's interesting that they got this model down to 1852 pounds, and didn't switch to the 911R tail lights. Maybe they made lightweight boxes for them?

[realgren]

Hi Jack,
have you taken a look at this website: https://www.superbrightleds.com/carbulb_notes.php

Under the section Turn signal issues with LED bulbs, they say:

LED brake/tail lamps will not flash with thermal flasher units due to their extremely low current draw. [...]
Another fix is the installation of Load Resistors which are wired across (in parallel with) the turn signal bulbs to simulate the load of a standard filament bulb.

I'm not an electrical expert, so if you find a fix, please do let us know. I am interested.

[Jack Olsen]

There's some confusion in the replies (which is fair enough, as the original post is LONG). There is no problem with the LED assemblies working with the conventional flasher relay. They come with the resistors installed.

What surprised me was that they would not work with an LED-specific electronic flasher relay. But that it probably because of the resistors, too.

[J-Mac]

Don't these guys have a lite weight tail assembly (tech9.ms) for sale? See post #123. Probably $$$s...

edit for link

http://www.impactbumpers.com/forum/index.php?/topic/17319-birth-of-a-rally-car-tech9-ruf-scr/page-7

[Jack Olsen]

Yeah, there are a few different products available out there. I don't think any one of them approaches my cost, which was $38 for the LED stuff and $0 for the scrap aluminum.

And for what it's worth: Tech9 claims to save 5.5 pounds from stock, while mine saves 6.4 pounds.

[JeremyD]

I made my own









https://www.youtube.com/watch?v=nrMjNak28jE



The only reason the yellow is different is because I used clear on the flashers and amber on the marker lights.



Similar concept though.

I got the square lights from superbrightleds and the round marker lights are from a trailer mfg company - they are 1" marker lights all LED's

[Jack Olsen]

That looks great, Jeremy. I wish I knew fiberglass.

I've got one last postscript on this -- a final little tweak with only a small weight hit.

Who knows why, but most of the rear lens has an etched pattern to refract the light. But on the forward section, the plastic is clear.



To fix this, the factory boxes include a lens piece. It weighs an ounce.



For six bucks, you can get a clear piece of refracting plastic that they use in suspended ceilings. You can cut it with ordinary scissors.



And it weighs very little. Not even enough to register on my scale.



Same function:



Here are the naked running light bulbs:



Refracted:



And covered with the lens:

[JeremyD]

I like that solution - very elegant

[TimT]

The LEDS I have on the back of my early 911 are quite bright they are big rig clearance lights that fit the 911R signal housing... and a adding a resistor to the turn signals allows the turn signals to work as expected. As always chasing a few ounces at the extrema of the car is an interesting exercise.

It's interesting that they got this model down to 1852 pounds, and didn't switch to the 911R tail lights.

My car weighs 1846# wet

[Jack Olsen]

Having done a lot to cut weight... the cars that are 500 pounds lighter just boggle my mind.

[wwest]

I bought the solid state flasher, took it apart and replaced the nichrome wire current flow sensing "resistor" with one higher enough in value to drop enough voltage with the lower LED current flow.

[jschmidt63]

Originally Posted by Jack Olsen

Having done a lot to cut weight... the cars that are 500 pounds lighter just boggle my mind.

It bobbles my mind the effort you guys make to shave a pound or ounces. More power to you, just an observation.

Reminds me years ago I through- hiked the AT trail and what some guys did for weight savings, like drilling holes in forks and toothbrushes when I was carrying beer and cookies...., but I guess it all adds up.

[froggert]

i'm going to attempt this soon, probably using led truck lights in a box like jack's. would you guys that have done the led conversion do it again? any words of advice before i go down this road (haha) and start ordering parts?

thanks.