Lighting Updates on the GTS

This new GTS is a pretty awesome car it’s in great condition and everything works pretty well, but that doesn’t mean it can benefit from some modern technology. LED lights are a fantasic upgrade for these old cars. The can produce more light (if needed), and consume far less power with is a good thing for cars that have lower output alternators like the 928.

LED technoloy has come a long way in a very short time. These days you can choose from a variey of colors, color temperature, as well as, lumen output (equivalent to watts). All which lends itself to my restoration ethos which is to improved performace while adhearing to the orginal style, or within the rehlm of what the manufacture would do.

Headlights, Fog lights, Auxilary Driving lights

I noted on the maiden drive that all the front facing lights, you know the ones that help you see, were all realitively dim dispite having the european H4 lenses and the distance control function.

On closer inspection, I noted the passenger side headlight was cloudy and full of condensation on the inside. The headlights and fog/aux assemblies had a thick plastic stone-chip protective coating applied. Which was great for protection, but the coating had yellowed and become cloudy from the elements. I decided to remove all the plastic coverings and give the assemblies a good cleaning inside. I used a hair drier to soften up the plasic covering which helped remove them and I used class cleaner to clean out the inside of the headlights and fog lights. The results left me with new looking assemblies.

I replaced all the bulbs LED equivelants with the same 6000K color temperature so they all look the same for drivers and myself. I looked for bulbs that have the LED precise same location as the OEM bulbs to preseve the focal points. Also, I looked for the brightest version possbile. I found I had to shop for several versions of the same bulb and try several, and return the items I did not like. I used Amazon which was great for my needs because of the return policy.

H4 headlights

These bulbs are fantasic and out perform the high end bulbs I purchased for my 1988 928 S4, and at a third of the price. There are a lot of really good H4 lights and I am sure you will be able to find something as good or better.

Fog Lights and Auxilary Driving Lights

The H3 LED’s are a more difficult story, its hard to find H3 LED’s that have the same output as the halogen that will fit in the smal space. These lights below come really close and are the brightest I have come across.

Interior lights

There are no less than 9 lights interior lights in a 928 that will illuminate when a door is open! This is a serious draw on the battery and will drain it flat in a hour. Most of the cabin lights use a common size festoon bulb available as LED. I choose to use “warm white” for LED cabin lights because it replecates the incandescent look. I tried brighter temperatures but the effect is odd and cold.

Also the factory Porsche interor lights are terrible, they have unprotected hot connections on the back side and are prone to shoring out.

A common upgrade is to use the rocker switches out of a late model VW Jetta/Golf. They look like they belog in the car and their slightly wider footprint is a better fit for the cutouts in the body panels. I was able to source several black VW lights and harness pigtails at my local salvage part supplier. I add male spade connectors to the pigtails to plug directly into the factory harness.

In addition to these lights, I updated the little red marker lights in the back of the doors.

I am also in process of an exterior light conversion to LED, that one is a little more tricky due to interaction issues with the bulb monitor, headlight relay, and fasher relay. All can be solved with a little trial and error. Currently, I have the headlights, DRL, Fog lights, Aux lights all converted to LED’s.I used the same 6000k color temperature for all the lights so the front is all the same consistent color. It is bright white, not blue, but certianly different from the original amber glow of the halogent bulbs. On this ROW model, I didn’t run into any weirdness with relays. The LED’s plus H4’s headlights are simply amazing at 2x the brightness of halogen bulbs. With the H3 fog/Aux, it’s hard to beat the light output of the halogen given the tight space. So I had to comprimize a little, to ensure all the lights were the same color, so I have some bulbs that are about as bright.

I am still sorting throug the correct bulbs for the brake/turn/rear fog bulbs. I should have an updated post next week. On thing people often forget is rear driving lights should be dim, so they dont compete with brake lights.

Tail lights

I really start to get an appreciation for just how complex car design is and how may factors are needed to consider for performance and safety when I see complexity in something as seemingly straighforward brake and parking lights. When converting to LED it’s easy to only look at the color of the bulb and then go for the brightest thing you can find. However, in the case with tail lights, that is certainly the case with brake lights. When considering driving lights or dual function driving/brake, or driving/fog lights it’s much more about creating contrast between brake and no-brake. So driving lights you really need to look at the lumen and ensure you are low enough to create a strong contrast in lumen intensity. The stock driving light is about 4-watts which equates to about 30-45-lumens. Finding a LED bulb with a low enough rating is not the easiest. Fortunately does a really good job and listing all these specifications, unlike shopping at Amazon or Ebay.

So when considering replacing the LED, consider the color and the brightness, as well as, the proper functionality. Here are the selections I made and some of the rationale behind the decisions:

Turn Signals and Relay

As soon as you install the LED turn signals you are going to start having some issues with the functionality of the linker system. You will get double flashing. I have tried several different version of relays and bulbs and had have varying degrees of sucess. I found this relay to work well with the bulbs that have chosen. CF13GL-02 LED Bulb Electronic Flasher 3 Pin Black European Flasher.

There are differences in bulbs used on the USA and ROW models. The USA models have dual function bulb on the front corner marker (1157 socket). I found that I had to purchase several differnt bulbs and try them until I was happy with behavior. On the ROW GTS, it was far less complex, all I needed to do was replace the relay because the GTS does not use the dual function bulb in front.

Bulb Control Module

When you replace the rear red lights with LED, the bulb control module will sense an error becuase there is no longer a filiment in the LED bulb. The module uses the incandescent filament as signal of connectivity. So when you replace with LED’s you need to address this. There is a really great write up on Rennlist on how to defeat the bulb control modual monitoring of the rear brake lights and rear driving lights. The modification is completely reversable. You can find the link here. I performed this modification on both of my cars.


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