I want to ask you if the tail lights from Boxster fits the Cayman. I found some very nice led tail lights on the internet, but they where only for the Boxster. What do you say?

Could you please post the internet link to the lights you mentioned. It is easier to provide feedback if we can see the items. Thanks!

Let say this ones: http://www.europerformance.co.uk/pag...html?id=131494

For me it looks like the ones we have an our croc.

I'd be real careful about buying those, they're not cheap. I see a few potential problems:

- It doesn't say whether these are for the 986 or 987 Boxster. If it's for the 986 then they definitely won't fit.

- If/when you wire these up, you may get a lot of OBD errors unless all the LEDs are regulated somehow. This doesn't look like a terribly easy mod to do from the electronic/wiring harness standpoint.

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Electrically, I would not expect this to be difficult. In fact, I would sort of suspect them to just plug in. However, LEDs will present a much different resistance to the circuit than a light bulb will. This is very likely to kick up an error in the lighting control module. In other words, I'd be surprised if after installing these the car did not keep harassing you about bad light bulbs in the rear.

There are ways around this, if you have some electrical skill, which may be what Interpol is referring to.

Yes, that's what I was referring to. Sorry, I should have clarified a little bit.

In order to prevent 'replace light bulb' errors you'll have to install an in-line regulator (usually a resistor) between the harness and the lights. Unfortunately I have no idea how to do this for this particular LED system because there are multiple LEDs and there is no information posted on the website about the specs of each.

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You'd almost have to assume that the manufacturer is including the resistors already. I added custom LED lights on my bike, and adding the right resistors took a minute of math and about $3 in parts. Surely, the light manufacturer here has done that.

There are other plug in light bulbs out there that faced the same issue, but must have the right resistors in them, since they don't cause errors.

Of course I COULD be wrong... They could be thrown together garbage (but the cost of molding the plastic required would betray that).

If I was a betting man, (and I am...) I would put my money on them working just fine.

Point proven. Resistors, relays, and so on. Addition of these devices to prevent the light bulb warnings will drive someone insane.

I cannot understand why Porsche didn't put LED tail lights in the first place! Even my new company Honda Accord has them.

The resistors you added on your bike are a bit different. Those were to make the 2 volt LEDs work on a 12 volt system. That means you need to displace 10 volts on the resistor. For ten LEDs, drawing 20 milliamperes each, you would use Ohms law dreivitave R = V / I. So, 10 / 0.20 = 50 Ohms. Piece of cake. I agree with you. I am sure the manufacturer of these lights included these resistors.

What Interpol is talking about is the fact that the Cayman has a light control module that measures the resting resistance of each light bulb when that bulb is not in use. If the resistance comes in higher than expected, it displays a warning to you that the bulb is bad.

LEDs are, as you know, Light Emmitting Diodes. What you may not know is that diodes have a biasing voltage (usually around 2 vlots for LEDs). Below that voltage, they will read as an open circuit. Above that voltage, they will not read as open but will use considerably less current than an incandescent light bulb and will therefore present a much higher working resistance. In short, the LCM will see them as a blown bulb.

So, to fool the LCM, you need to determine what resistance it's looking for. You can do that pretty easily with an OHM meter, but you will quickly discover that a resting light bulb has a resistance that is very low. Maybe 2 or 3 Ohms. Now you can wire a 2-3 OHM resistor in parallel to the circuit to fool the LCM, but such a low Resistance is going to generate a lot of heat (about as much as the bulb would have). On the brake lights, this might not be a problem because they don't stay on long. But the parking lights stay on very long and will create lots of heat which will end up damaging anything the resistor is touching.

OK, no problem. Just add a normally closed relay to the circuit. Let it present the resistance when the circuit is de-energized because that's when the LCM is testing the bulb. And when the circuit energizes, have the relay drop the resistor out of the circuit because the LCM doesn't test the bulb when it's on. That will save the heat issue.

OK, so let's see. On a Bosch 20/30 relay, contact 85 goes to one side of the new bulb (LED), 86 goes to the other side. 30 ties in with 85, and 87a connects to one side of the resistor, the other side of which goes to 86. Now duplicate this once for every bulb the LCM is expecting to see. One for the right brake light, one for the left. One for the right parking light, one for the left, and so on.

Before you know it, you have 4 - 6 relays and resistors and a rats nest of wiring mods.

I would be very surprised to find out that the lights have this inside already.

Most of the LEDs I have seen have a 1.4V to 1.5V voltage drop, and there are others that have a built in resistor that operate at 5V at about 20mA ( regular diodes have a drop of about .4 to .7 V depending on the material they are made of ).

In any case the points made by Gator Bite are valid, and unless the light's maker does a proper design they will be a pain to install. I would say, that if you purchase something from a good retailer, and they have a good return policy, it might not be an issue - get it, try it, if it does not work well return it.

In general, I think there is a move away from tail lights that look like they are LED - they still may use LED bulbs as they would last a lot longer, and use a lot less power. I personally like LEDs when they are well done :-)

...um - I knew that... I was just testing you.