What Kind of Resistors Are You Supposed To Use For LED Conversion?

[xDan]

If they are in series connected to your lighting circuit, a single 470 ohm resistor should drop the voltage enough. It depends on how many LED's in the circuit though. The more you have the less resistance required. I'm not positive on dash lighting but all lights in there shouldn't be one long circuit in series. Even my 71' Chevy has them grouped into several parallel circuits.

 

[Justinj360]

If they are in series connected to your lighting circuit, a single 470 ohm resistor should drop the voltage enough. It depends on how many LED's in the circuit though. The more you have the less resistance required. I'm not positive on dash lighting but all lights in there shouldn't be one long circuit in series. Even my 71' Chevy has them grouped into several parallel circuits.

Okay I guess I'm not sure if they're in series or parallel. What I did was I removed each old light and replaced each one with 1 LED and 1 resistor.

 

[Blackie]

Have you seen this write up on the Master How To List:
http://www.gmfullsize.com/threads/led-interior-change-over-how-to.70072/

Master List:
http://www.tahoeyukonforum.com/threads/how-to-master-list.2322/

Found in the tech section:
http://www.tahoeyukonforum.com/forums/tech-info.54/

 

[xDan]

Do you have the resistors all on the positive side? Did you do a voltage drop check across the resistors on install? Take your undimmed voltage drop from the dimmer circuit output to chassis ground then subtract the voltage drop across the resistors and that gives you what the diode is seeing. Obviously, you will have to pull out your dash again to find out what is going on. When you overdrive LED's they burn out. USUALLY when they go they stop allowing voltage through but sometimes they will bridge and not glow but allow power to go both ways through it. When you buy bulk LED's, some of them will handle less voltage than others, sometimes it's less that what they are "rated" for, you test it and it goes super bright, gets too hot and ****, gone.

 

[kwOH]

I sent mine to Circuit Board Medics, $150 and they replaced all the stepper motors and put in all LEDs.

https://circuitboardmedics.com/

 

[Justinj360]

I sent mine to Circuit Board Medics, $150 and they replaced all the stepper motors and put in all LEDs.

https://circuitboardmedics.com/

Eventually I will send my cluster in to be upgraded to LEDS and also a transmission temp gauge. I definitely don't want to screw with that myself.

Do you have the resistors all on the positive side? Did you do a voltage drop check across the resistors on install? Take your undimmed voltage drop from the dimmer circuit output to chassis ground then subtract the voltage drop across the resistors and that gives you what the diode is seeing. Obviously, you will have to pull out your dash again to find out what is going on. When you overdrive LED's they burn out. USUALLY when they go they stop allowing voltage through but sometimes they will bridge and not glow but allow power to go both ways through it. When you buy bulk LED's, some of them will handle less voltage than others, sometimes it's less that what they are "rated" for, you test it and it goes super bright, gets too hot and ****, gone.

Actually... I just remembered the how-to thread I was following (no idea where it was) said it didn't matter which side of the LED the resistor was on. I thought that was weird but I went along with it. Could that be my problem? I didn't do any tests on them before install, other than plugging them in to see if they worked.

Have you seen this write up on the Master How To List:
http://www.gmfullsize.com/threads/led-interior-change-over-how-to.70072/

Master List:
http://www.tahoeyukonforum.com/threads/how-to-master-list.2322/

Found in the tech section:
http://www.tahoeyukonforum.com/forums/tech-info.54/

I might have missed it but I did not see my specific model in those threads.

 

[xDan]

Whoops, it doesn't matter what side the resistor is on, just that it's there on each LED. The problem is the current running through your LED's. 470 ohm isn't enough. V=IR. V=volts, I=current in amps, R=resistance in ohms. Your alternator while running typically outputs 13.5 volts but can peak at 15V or something very close to that. Now the rated maximum current that goes through the LED's you have is unknown but the forward amperage is 20mA, or 0.02 amps. At typical system voltage of 13.5 and full bright on the dimmer pot, with 470 ohm resistors the current passing through your LED's is 29mA. At 15V it's 32mA and at 12V they are getting 26mA. Using the dimmer, your LED's will start to turn completely off at 9.4V. So until we know the maximum current that the LED's can handle, we can't say for sure what resistors to use.

It looks like the dimmer circuit is not PWM and just doesn't play nice with LED's. Did you notice any color shift when the brightness changes or difference in color between one LED and the next? Could just be cheap LED's like I said earlier or your connections are going bad from vibration or a weak solder joint.

 

[Justinj360]

Whoops, it doesn't matter what side the resistor is on, just that it's there on each LED. The problem is the current running through your LED's. 470 ohm isn't enough. V=IR. V=volts, I=current in amps, R=resistance in ohms. Your alternator while running typically outputs 13.5 volts but can peak at 15V or something very close to that. Now the rated maximum current that goes through the LED's you have is unknown but the forward amperage is 20mA, or 0.02 amps. At typical system voltage of 13.5 and full bright on the dimmer pot, with 470 ohm resistors the current passing through your LED's is 29mA. At 15V it's 32mA and at 12V they are getting 26mA. Using the dimmer, your LED's will start to turn completely off at 9.4V. So until we know the maximum current that the LED's can handle, we can't say for sure what resistors to use.

It looks like the dimmer circuit is not PWM and just doesn't play nice with LED's. Did you notice any color shift when the brightness changes or difference in color between one LED and the next? Could just be cheap LED's like I said earlier or your connections are going bad from vibration or a weak solder joint.

Okay, I follow you for the most part. I think you are correct about the LEDs turning off around 9.4V because they're off completely before the dimmer wheel reaches the bottom. I did not notice any color differences between the LEDs. I'm sure I did a good job with soldering the connections but I am by no means an expert with that. This is the second vehicle I've done this on just so you know.

So what are my options for fixing this? Getting the right LEDs and resistors?

 

[xDan]

Well you have 100 of them...If it was me with this issue, I'd check my solder joints and look for burned out LED's before buying more of them and waiting. I've read that PWM dimmers work best with LED's but the power circuit on these trucks connect to a serial data line and are grouped with several other systems. I think it monitors amperage draw and can give a code. I couldn't find any specific details about it however...I'm definitely not changing mine out.

 

[Justinj360]

Well you have 100 of them...If it was me with this issue, I'd check my solder joints and look for burned out LED's before buying more of them and waiting. I've read that PWM dimmers work best with LED's but the power circuit on these trucks connect to a serial data line and are grouped with several other systems. I think it monitors amperage draw and can give a code. I couldn't find any specific details about it however...I'm definitely not changing mine out.

Yeah but it's not like they're expensive. Okay I will review my solder joints first. So I checked the dimming this morning and they actually turn off completely when the dimmer wheel hits the bottom (as they should). I'm not sure why I remember them turning off before that point. If you wouldn't change that thing out then I definitely won't either!