Or, theirs is the same and their fine with it. You may be surprised what people consider "good enough". When we buy something, we assume it's manufactured correctly. Unfortunately it isn't always true and people accept it as is.
Inline Resistor - HOT
- Thread starter thedoughboy
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- Thread starter
- #22
After refreshing my memory I found out a few things. The resistor was installed to correct a cruise control malfunction. Without the resistor, the cruise control turns off when using the turn signals. It also turns off when the brakes are applied.
The resistor was connected to the 12V + brake wire and the ground. See the picture for reference.
The resistor was connected to the 12V + brake wire and the ground. See the picture for reference.
The cruise control is supposed to cancel when you hit the brakes.
Don't you want the resistor on your turn signal instead?
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- #24
Well, one would think. I installed the resistors ~7 years ago. Everything works as designed with the resistors installed on the brake line. I just pulled the resistors and the cruise control cancels when I use my turn signals. Interesting enough, the brightness of the brake and tail lights are not affected (visually) by the resistors presence.
I went through some old threads and this is the fix that was presented to me. So, I took it on and it worked. I did not know the resistors would get too hot to touch and melt the surrounding plastic. I did not mount them to the sidewall. When tinkering on my truck I noticed the damage. I have since pulled the resistors and am in the process of going a different direction.
As always, any insight is greatly appreciated.
So as stated by others your resistors wattage rating is likely too low for the wattage of the LED lamps, even if the LED lamp is 5 watts and you use a 5 watt resistor it may create a lot of heat. If you oversize the resistor to say a 10 watt it'll do the same thing with less heat.
Think of electrical stuff the same as you would a town waters supply. The wires are the pipes, the voltage is the PSI in the system, and your in line resistor is functioning as a valve. Using resistors in line to reduce voltage makes them act like a partially closed valve in a water pipe, the higher the Ω value of the resistor = the more closed the valve is on the water pipe. Now the voltage is pushing electrons through the resistor to the device, and the higher the flow through the resistor the hoter it gets (this can happen with under sized valves in high pressure water systems too).
Now with water you can just let it flow out of the valve and be done, but in electrical circuits you have to size the resistors capacity to handle flow (wattage) to the demand of the device which you are powering. So it sounds like your resistor is not rated to handle the flow it's experianing, with a multi-meter set to DC amps you can figure out the draw of the lights then back into what wattage resistor you need, I'd suggest sizing it at a factor of 2 (soI'd choose a 10watt resistor for a 5watt LED bulb).
WITH ALL THAT SAID, you're not really handling the issue correctly. You are trying to filter out a small spike in voltage that happens over the course of a couple of milliseconds that is coming from your turn signals LED bulbs when you cancel them. In electrical circuits, we call this noise, and its common for that noise to bounce through circuits with shared grounds (brake lights) and cancel the cruise control.
You really should be adding a simple Passive Low Pass Filter, which is what they use in stereo installs all the time to properly tune tweeters mainly. With an inline resistor and a capacitor bridging from between the LED bulb and resistor positive wire to ground. The resistor is still functioning as a valve, but the capacitor is what provides the absorption of the spike.
Let me explain using the towns water supply as an analog again. The water is supplied from the water tower and runs through a valve, then after that, it halfway fills a small tank before going to the end user. Well if there is suddenly a short yet high-pressure reversal of flow from the end user, the tank will act as a buffer and that pulse flow won't shock the whole system by trying to return to the water tower. How does this relate to electronics? let's recap; the water tower = the battery, the valve = the resistor, the tank between the valve & end user = the capacitor.
I put this type of filter on my e30 when I did my "one touch 3 blink mod". The circuit looks like this (keep in mind you have to size the resistor & cap correctly but its not that hard):
Think of electrical stuff the same as you would a town waters supply. The wires are the pipes, the voltage is the PSI in the system, and your in line resistor is functioning as a valve. Using resistors in line to reduce voltage makes them act like a partially closed valve in a water pipe, the higher the Ω value of the resistor = the more closed the valve is on the water pipe. Now the voltage is pushing electrons through the resistor to the device, and the higher the flow through the resistor the hoter it gets (this can happen with under sized valves in high pressure water systems too).
Now with water you can just let it flow out of the valve and be done, but in electrical circuits you have to size the resistors capacity to handle flow (wattage) to the demand of the device which you are powering. So it sounds like your resistor is not rated to handle the flow it's experianing, with a multi-meter set to DC amps you can figure out the draw of the lights then back into what wattage resistor you need, I'd suggest sizing it at a factor of 2 (soI'd choose a 10watt resistor for a 5watt LED bulb).
WITH ALL THAT SAID, you're not really handling the issue correctly. You are trying to filter out a small spike in voltage that happens over the course of a couple of milliseconds that is coming from your turn signals LED bulbs when you cancel them. In electrical circuits, we call this noise, and its common for that noise to bounce through circuits with shared grounds (brake lights) and cancel the cruise control.
You really should be adding a simple Passive Low Pass Filter, which is what they use in stereo installs all the time to properly tune tweeters mainly. With an inline resistor and a capacitor bridging from between the LED bulb and resistor positive wire to ground. The resistor is still functioning as a valve, but the capacitor is what provides the absorption of the spike.
Let me explain using the towns water supply as an analog again. The water is supplied from the water tower and runs through a valve, then after that, it halfway fills a small tank before going to the end user. Well if there is suddenly a short yet high-pressure reversal of flow from the end user, the tank will act as a buffer and that pulse flow won't shock the whole system by trying to return to the water tower. How does this relate to electronics? let's recap; the water tower = the battery, the valve = the resistor, the tank between the valve & end user = the capacitor.
I put this type of filter on my e30 when I did my "one touch 3 blink mod". The circuit looks like this (keep in mind you have to size the resistor & cap correctly but its not that hard):
- Thread starter
- #26
@SmokingRocks Thank you for your clear explanation. I think I am a little better at plumbing than electrical 
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Thanks, I use to loathe anything electrical until I was forced to deal with the PO's hatchet job he had done to the harness. Once I figured out it was the same concept as water flowing through pipes it made a lot more sense.@SmokingRocks Thank you for your clear explanation. I think I am a little better at plumbing than electrical
Voltage = PSI
Wattage (amps) = flow rate
Wires = Pipes
Battery = Water Tower
Resistance (Ohms) = Flow Regulator
Resistance is important because the lack of understanding this has been the cause of many modified vehicle fires.
If you have a device 10 feet away from the battery that draws 300 watts of power or 25amps (300watts /12 volts = 25 amps) of power and the wire supplying it is only 18 gauge that's an issue. The wire is too small of a gauge to carry that much flow that far of a distance, if not fused correctly the entire wire can get so hot it can melt the insulation eventually finding a combustible material then start a fire that you can't put out.
this is why it is important to consult charts like this when running aux wire, it is also why we teach that fuses are sized to protect the wire run NOT the device.
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This sounds like a diode on the brake line would fix it.
A problem I've seen with some LED combo lamps is they allow power to back feed other circuits. When the turn signal is on, yours probably pulses back the brake wire. The cruise must be monitoring that.
A diode might work, the issue with them is they usually drop the forward voltage (voltage seen after the diode) considerably, sometimes enough to induce issues with the device needing power. Also you'd need a pretty high capacity (wattage) diode to handle the forward current while still filtering out the millisecond long under voltage backfeeds from the signals. In my experience, the higher wattage diodes don't do as well at stopping the super fast lower voltage return spikes.