LED Blinker swap question

[Crowz]

Today my passenger side front blinker bulb blew. I found out by it blinking fast as I had coded out the warning

Anyways I'm ordering led bulbs to go back in place of them. They are the kind that are white in place of amber when serving as parking lights and turn amber when you turn the blinkers on. Should look pretty cool.

The question I have is will the new LED blinker bulbs cause the fast flashing I'm getting with the blown bulb?

Is that a coding thing I need to do to it or will I have to add resistors. I loath resistors since they defeat one of the reasons for having LED's in the first place is low power consumption.

[Zulu95]

Most likely you'll need either resistors or capacitors. Going back more than a few years here: Something like 1500 - 2500uF caps worked if I remember correctly. (They also work for the flickering caused by adaptive brake systems.) Failing that load resistors or a bulb in circuit. The latter are a pain because of heat problems (or bulb breakage.) so placement is important. i did a quick test with resistors once and was surprised how hot they got.
My LED rear lights have loading system built right in which I believe is a cap for each side.

[crystalworks]

It will depend on your bulbs. My front LED blinkers did not need resistors. My rears did.

I agree with you that it sucks to have to waste energy as heat just to fool the computer...

[wpoll]

For what it's worth the caps and resistors do different things.

The caps smooth out the PWM pulses used to power the incandescent lamps on the later cars. The caps act as an averaging device. They stop the flicker during normal operation (but not usually the cold monitoring at start up). They sometimes also work to "slug" the cold and hot monitoring, although this can be hit or miss.

The resistors act as a dummy load for the cold and hot monitoring by the LCM. They stop the dash warnings etc. Coding out cold and hot monitoring should remove the need for resistors.

So depending on which lamp circuit you are putting LEDs into and if you want to re-code, you may or may not need caps, resistors, neither or both!

[crystalworks]

Originally Posted by wpoll

For what it's worth the caps and resistors do different things.

The caps smooth out the PWM pulses used to power the incandescent lamps on the later cars. The caps act as an averaging device. They stop the flicker during normal operation (but not usually the cold monitoring at start up). They sometimes also work to "slug" the cold and hot monitoring, although this can be hit or miss.

The resistors act as a dummy load for the cold and hot monitoring by the LCM. They stop the dash warnings etc. Coding out cold and hot monitoring should remove the need for resistors.

So depending on which lamp circuit you are putting LEDs into and if you want to re-code, you may or may not need caps, resistors, neither or both!

^I second the above. But with the caveat that some LED bulbs (especially switchbacks) will require the installation of resistors to work properly. I'm not sure of the electrical reason for this... but I've run across switchback applications that will not work without resistors.

PS: My rear cold/hot monitoring is coded off, but the rear still required resistors before the bulbs would illuminate.

[wpoll]

Originally Posted by crystalworks

PS: My rear cold/hot monitoring is coded off, but the rear still required resistors before the bulbs would illuminate.

There are always exceptions!

My guess is that caps might work here in place of resistors - the resistors are acting like the incandescent filaments and "averaging" the PWM pulses, smoothing them to a near-DC voltage, which the LEDS are then happy with.

The whole LCM system was designed with the incandescent lamps as an integral part of the circuit design, so removing them requires all manner of tricks the get things working again.

[Zulu95]

I think the resistors work by providing the correct current draw which the LKM senses and assumes as normal "bulb" operation. Because the voltage supplied by the LKM is actually a higher frequency AC the reactance of caps performs in the same way.

[wpoll]

Originally Posted by Zulu95

I think the resistors work by providing the correct current draw which the LKM senses and assumes as normal "bulb" operation. Because the voltage supplied by the LKM is actually a higher frequency AC the reactance of caps performs in the same way.

You are correct - that's what is happening. But the correct current draw (as far as the LKM is concerned) is only used to monitor bulb status. The voltage to the bulbs is still (as you say) a form of AC and this will cause the LEDS to flicker. A capacitor with smooth this "AC" (PWM actually) to a DC-like power supply and the LEDS operate correctly.

What I'm guessing at is why the resistor has a similar smoothing effect!

[Crowz]

Well I'm going to try the led switchbacks and a resistor harness. I just hope the harness is plug and play for this. I bought something similar for my vette and ended up having to up the harness I bought and splice it into the car's wiring since there wasn't enough clearance for the sockets on the harness kit.

[bcredliner]

Decent LED options will come with anything you need so they work properly.