Questions about LEDs for Instruments
 

Hi All,

I stumbled upon some posts about upgrading the lights for the instrument cluster to LEDs for some brighter lights. The lights I ordered were the WLED miniature wedge base bulbs, since they should be the 194 replacement. The problem I'm having is that the bulbs won't come on at all. The only issue I really saw that was common in the past threads was the lights being polarized, but I have tried them all both ways with no luck. If I saw the original bulbs back in they come on no problem. Does anyone have any ideas?

This is for the 1986, so the newer dash/gauges.

Also, would anyone have the part number for the smaller bulb holders, such as the one for the turn signals or warning lights? I appear to be missing a few and would like to replace them as well.

Thank you

944 LEDs
* 74-xHP Wedge Base LED Bulb (10 needed) #This is for speedo, rpm, oil, volt, clock, and centerconsole#
* B8.5D Instrument Cluster LED Bulb (7 needed) #This is for left gauge# I would get 3+ more cus they are pretty easy to break when putting them in.
* WLED 6-LED Bulb (1 needed) #This is ONLY for the battery light in the dash#
* 3022-x4 LED Festoon Bulb (1 needed) #This is for the glovebox#
* 4211 LED Festoon Bulb (2 needed) #This is for the luggagelight in the back and domelight#

That's interesting that normal (incandescent) bulbs work OK in the instrument cluster, but LEDs won't won't light up. The only one that I can think of which likely would be a problem if changed to an LED is the ALT (alternator) light. That's because the wire going to it from the alternator needs to have a certain amount of current going through it when the light isn't lit, and an LED has essentially NONE going through it when it isn't on, except for the VERY TINY amount of reverse leakage current.

But that doesn't explain why the other warning lights, as well as the ones that provide the back-lighting for the cluster (I assume that is the MAIN issue that this thread is about) won't work when fitted with LEDs. Although I have other things that need to get done, I will take a look at the wiring diagram to see if it provides any clues to why this situation is occurring, if I get a chance.

This is starting to look like a tricky one already. Hopefully someone who knows what the deal is will chime in.

Is your dimmer full on (bright)? If it isn't the regular bulbs will light but LEDs will not, seems to be your problem.

With the dimmer on full, if your regular bulb lights and the led doesn't work both ways, you either have the wrong (voltage) led or it has blown.

With the LED's the dimmer will not work - because of the circuitry if even one of the LED's are wired backwards none of them will work. The LED's need to be wired with + to + and - to - only. I have them in my 85.5 now, but ran into the same problem of getting the positive wiring correct from the start. My LED's came with two wires off of them so mine needed to be soldiered in place to the contacts of the old bulbs

Do not quote me on this as it's been quite awhile since I did them - but I'm thinking that my red wire off of the LED went to the bottom of that bulb contact (LED had a short red wire and a short black wire) - the contacts for the old bulb were upper and lower spots on the circuit board, so when twisted in place the bulb would contact the circuitry correctly.

Christmas is nearing - Has any one tried LED's on a tree yet - LOL

That makes sense.
 

Will the LEDs dim properly using the factory dimmer?

Hah! I've already cannibalized a string of tree lights from 2 years ago, for the purpose of using the LEDs to upgrade various other low-voltage incandescent bulbs. For use with 12 volts, a 330 ohm series resistor is required. And of course polarity needs to be observed.

Light Emitting DIODES

LEDs do not dim period - they are either on or off.

Off the subject - I wonder if a 12v. cell phone charger that plugs into the wall will work with LEDs on the tree ...LOL

The ones that the OP will dim actually. I have them in my car currently. The only issue I have had is that at least 1 bulb will burn out. Its kind of annoying out of the past 2 sets at least 1 LED will go bad. Its very frustrating.

Thanks for all the responses guys. I will definitely check the dimmer, but like billy said, these ones should dim at least. From my understanding, they also have a resistor built into them.

Coca, I'm guessing you wired yours yourself? I'm not sure if these will need to placed like yours, since they should be direct bulb replacements.

Dimmable LEDs won't dim using a potentiometer. A pot adjusts voltage, LEDs, even dimmable ones work on current not voltage. The dimmer on the 944 is a pot/rheostat that adjusts voltage only.

To make this work you need to wire a Pulse Width Modulator between the 944 pot and the dimmable LEDs that you wish to dim. Then your LEDs won't blow.

This is the PWM circuit you need. Many of the LED suppliers sell them as a plug and play box. You wire the 944 dimmer switch as the 50k rheostat shown in the diagram and your dimmable LEDs (with resistors) as shown.

http://i1196.photobucket.com/albums/...s/7e358415.jpg

That was my first thought as well - bypass the potentiometer in the dimmer so the LEDs see full 12v

I'm sure that the potentiometer in the factory dimmer has a resistance that is FAR lower than 50K, but it still might work in that circuit.

I understand that PWM is the "proper" way to dim LEDs,. But I'm NOT seeing how the "dirty" method of hooking the LEDs straight up to the pot (like the incandescent bulbs are) will fry them. The only issue that I can think of is that they will dim completely out when the pot is moved only part of the way down from full. But it should still be a usable setup.

Is there anyone who HAS done it that can confirm this?

Wiring straight to the dimmer WILL fry them. You will exceed the current rating of the LEDs and eventually they will blow.

As I said they they will dim by current only and you are adjusting voltage. By dimming them with voltage you are not only decreasing the forward voltage of the LEDs but are raising the current excessively. Think about it, the formula is I=W/V. Wattage (W) is constant in the circuit, adjust the voltage (V) down and the current (I) goes way up.

As to that PWM circuit I posted it's an example. The 50k resistor can be any number you want.

Here's the scenario, and if someone can tell me how to post a Photobucket video here I'll show you an example.

With the dimmer full on you are getting 12v to the LEDs and they will work fine.

Start dimming slowly and the LEDs will dim until they see about 10v when they will turn off.

At that point you are only using a fraction of the 944 dimmer switch range.

Also at 10v you have increased the current to the LEDs. So, if they don't cut off from lack of voltage they might blow from excessive current.

Mass produced LEDs have a high tolerance meaning they are not all produced the same. There are a lot of variances even in the same batch. Some might turn off at 11v some at 9v.

That is why some of your LEDs will burn out sooner than others in the same circuit.

One other thing. You cannot use an LED in your charge light. It works by differential voltage unlike a regular circuit. You can use it in your turn signal light, some people say you can't but there is no reason it wouldn't work.

Again, I've done all this and will post a video if you tell me how to do it.

I installed the WLED-5 units from superbright about 4 years ago and they work fine with the dimmer. Not trying to discount what anyone has posted, just sharing my experience on the subject.

My $.02
A.J.

Yes the WLED-5's for the light tunnels have a high current tolerance so they tend to last longer than the other LED panel lights.

Tell me AJ, do they dim like before or just at the top range of the dimmer? Also when you dim do they dim ok to start with then suddenly cut off?

Mine used to do just that until i fitted a PWM so am curious about how yours work.

Mine dim as well although I have gotten 1 bad bulb in each batch. I will order just one new one and see if they last.