I just installed red LED brake/tail- lights on my 85 GSLSE. The tailights are clear on my car therefore it was necessary to install red light-bulbs. The LEDs are much better looking than the typical incandescant bulbs which I have been using. If you would like to see the clear tailights they are at: http://www.dcee.rotarymaniacs.com/tu...exnewlite1.jpg

Now... the problem.... Whenever I step on the brake pedal the dummy light on the dashboard lights up signifying that the brake light bulb is out. I believe this is happening because the resistance in the LED light bulbs is so low. Does anyone know how to correct this? Do I need to install a resistor for each bulb? Total current for the LED is 90mA at 13.8 Vdc -Verses- 2.6A for an incandescent bulb. (I got this off LED bulbs website - http://www.jamstrait.com/specs.html).

If there are any electrical engineers out there, let me know what you think. What size resistor should I install? In series, in parallel?


Thanks
DannyC
www.dcee.rotarymaniacs.com

 

Send a PM to a user named "Manntis" he sells them on his site and he may be able to help you with this.

 

Do you have access to a wiring diagram? Do you have a multi-meter? If so, I think I can help you through this one. It think there is a wiring diagram somwhere online, but I can't remember where.

Anyway, on to solving the problem. On page F of the diagram, it shows the brake light system (stop light in the book). You have a stop light switch that is activated by the pedal. You have a stop light checker just to the left of the connector for the stop light switch just behind the dash (if seated in the driver seat). You'll notice that there are some internal resistors drawn on the stop light checker. It works like this...

You step on the brake. the W (white) wire at that point sees the system voltage of 13.8 or thereabouts. according to the diagram, we don't want the GL (Green w/Blue stripe) wire to go low (grounded), which means the warning light goes on. OK, so now on to business! In order for the opamp to not turn on the transistor that feeds the warning light, more voltage has to be dropped by the strait through resistor than the other resistor next to it. Since your new LED lights don't draw much current, the strait through resistor isn't dropping enough voltage, and the light is coming on. It is impossible, without dismantling this sensor (I don't know if its sealed), to make the system work as it was originally designed. You have two options to disabling the system.

1. cut the green w/blue stripe wire (GL).
2. add a low impedance resistor(10 ohms might work) in paralell with the LED lights.

I would chose the first, because the second, needlessly converts the electricity that the alternator is makeing into heat, while the first only disables the warning system, and its cheap.

 

I would agree with above, if you cut the wire, you can always re-solder it together if you ever need to replace or swap the original bulbs back.

 

I think I will be cutting the wire. It is more energy efficient!

Thanks guys for the quick response's. I'll let you know how it works out.

 

If your talking about the bulbs i'm thinking of. they are not a 1157 replacement (2 elements ) thats why the dash light come on. the are only a brake lamp bulb.
install the leds on the inside ( next to reverse lights) and leave the center alone,, turn on parking lights,,only the centers come on,,right ??.
having checked the link above, you'll need to buy there bulbs and etc.

 

The ones I have are the replacements for the dual elements. They light up perfectly fine- when braking and when not braking.

 

1156 are on/off only. 1157 are on/on righter/off (brake lamps, front corner signal/running light bulbs, etc)

Some manufacturers build a resistor into the base, some do not.My guys are adding a resistor to the amber LEDS so they'll flash at the same rate as stock, but this is a week or two away from completion

 

I kinda like the quick flashing thing... if you mean quick on and off and not just a faster rate... like the busses around here have LED lights, and they're either off or on, not fading from on to off or off to on....

Jeff

 

Yeah I like it to. The response time for the bulb to light up is quicker.

 

The light on the dash comes on when there is TOO MUCH resistace.

removing the bulb causes the light to come on

removing the bulb causes infinate resistance.

 

?????? ??????

 

Breaking a circuit (removing a bulb, cutting a wire, etc.) creates ZERO resistance, because there is ZERO current flow. Resistance is impedance to FLOW.

 

Wrong....zero resistance is just that, no resistance to electric flow, but this is usually only seen in circuits cooled to near 0 degrees Kelvin...Infinite resistance means the resistance in the circuit cannot be measured because the electrical circuit cannot be completed....

 

Alright, I conceed I was semantically incorrect.

However, HIGH resistance as postulated by the poster above is not caused by removing a bulb (though infinite resistance is, as you stated). A broken circuit is the result. A resistor built into the LEDs, as Rotorhead.ca is having crafted, will restore the light circuit to the original level of resistance offered by the tungsten bulb, rather than the lower resistance offered by the LED cluster, solving the dash light warning problem

 

How much for your setup, Manntis? (too lazy to drift to your site...call it a quick quote...)

 

$29.95 for 4 bulbs, plus shipping. Your choice of 4 red 1157 LED clusters for your brakes, or 2 amber 1156 (rear signals) and 2 amber 1157 (front bumper running lights/turn signals)

http://www.rotorhead.ca/detail.php?adid=22

 

Manntis
i guess I shoulda bought them from you. Well, I am going to get 2 amber ones from you for the rear blinkers once you build the resistor into it. Do you know what size resistors are to be used for the brake lights if I choose that route? One resistor for each bulb?
Thanks

 

One resistor for each bulb, and the guys are finalizing the R&D (outside supplier - a family business that takes prie in their work)

 

Kewl!, wait for those to come in stock before shipping me set over, - Ok?

 

ALready anticipated that, Alex. I know you like to have the best of the best

 

It's not semantics. In the case of the stop light circuit, high resistance is caused by removing a bulb.

82streetracer was right: the warning light comes on when there's too much resistance. When a stop light bulb is removed or broken it does increase the resistance in the stop circuit.
There are four bulbs wired in parallel to the Stop Light Checker. When one section of any parallel circuit is removed, the resistance of the circuit increases.
Example:
1/Rt= 1/R1 + 1/R2 + 1/R3...
If R1, R2, R3= 10 ohms each, Rt= 3.33ohms.
Now make R3 infinite (i.e., remove a bulb): Rt= 5ohms.

Sorry. If the led bulbs draws less current, they must have a higher resistance. The resistance of the LED's will have to be decreased, which can be done with a resistor in parallel.

As the total resistance in a parallel circuit is smaller than any of it's branches, the resistor would have to be smaller than the original bulbs resistance.

Just for fun:
-The normal bulb is 27Watts (power). As P = VI (power=volts x current), at 12v the current through a bulb is
I = P/V = 27/12 = 2.25A, (not 2.6 as the web site mentioned).
Using Ohm's Law, V=IR (voltage = current x resistance), the resistance of a normal bulb should be
R = V/I = 13.8/2.25 = 6.1 ohms.
-you said the led bulbs draw 90ma @ 13.8v, so again
R = V/I = 13.8/ .090 = 153.3 ohms.

So you want 6.1 ohms total, not the 153.3ohms.
-Using the equation above for total resistance in a parallel circuit, with Rt = 6.1:
1/6.1 = 1/R + 1/153.3
The resistance to add is R= 6.35 ohms, close to the original bulb as would be expected. Closest standard values are 5.6 or 6.8 ohms. But the wattage would have to be around 30, similar to a regular bulb. That's a big resistor.
You could just jump a regular bulb in place of a resistor; the effect would be similar, but a little questionable. I have no idea what they put on the production bulbs; I've never seen one. (Maybe Manntis will let us know once he has recieved some. )

As previously mentioned, you may want to just disable your Stop Checker and keep an eye on your bulbs. You could unplug it and jump the White and Green (diagonal contacts in the connector) instead of cutting the wire. You wouldn't want to screw the LEDs up. (Although I'm sure Manntis would appreciate the business. )

-John

 

fatboy7, is this the same diagram as you have?

This is from the '84 wiring diagram. No opamps here, just a relay, 1 resistor to turn on the transistor, and a diode to protect the transistor from the relay coil. Just wondering if you have a diagram that I don't.

-John.

 

The light in car dashes comes on as a result of the drop in resistance caused by substituting LEDs for bulbs. This happens with volvos, mazdas, etc. The solution is to add a resistor, which a few of the higher-quality (and higher priced) LEDS already have, and the problem goes away. I'm endeavouring to bring this higher quality to 1st gen owners for less than the price of 4 APC LEDs.

 

O.K.
I can only presume that anything I said above made no sense to you.
You say I'm wrong, but not why. I'm not on the forum that often, but didn't you say you were an Electrical and Mechanical Engineer?

Can you explain to me how an LED bulb can have a drop in resistance along with a drop in current, when the simplest of formulas says otherwise?

V = IR. If resistance goes down, current must go up.

Hey, if you're right, you're right: I don't mind being wrong.

I'm just asking for details to counter mine so that I know what you're talking about.

-John