Right Resistor To Use???

Hey Guys, First time poster, long time reader!

I've got sort of an elementary questions, but I'm pretty sure I've came to the right place.

Ok, about a month or so ago I installed an aftermarket HID headlight kit into my car. The kit basically removed both 9007 bulbs and replaced them with H7's (I believe)? Well, long store short, they used a seperate power and ground circuit and just plugged into one of the existing bulb sockets just as a signal for a relay.

Install was easy and they work great. I really want to keep them, but I am sort of annoyed by one small problem.

I think my car has some sort of system that alerts me if a bulb burns out. The high beam indicator on my dash lights up slightly at all times. I;m pretty sure this is because I just have one headlight bulb socket unplugged and taped up with electrical tape.

My solutiom was to install a resistor in my unplugged bulb socket. I had a few different resistor values in my toolbox. When I tried a 10ohm (1/2 watt), the high beam indicator went out and worked perfectly. However, about 10 seconds after being plugged in, the resistor burnt up. So I connected two 10ohm resistors in parallel. Worked! then Poof, let the smoke out. I only had a 1 meg ohm in my tool box left. This one didnt work. It acted the same as not even having it in there.???

So I come to you needing help.... Just wondering what resistance value or combination of values I should install in order to "fool" my car into thinking the headlight bulb is still plugged in.

All I know......

-Stock headlight wattage is 65w
-Battery/Charging system runs at 12.6v-14v

What value, wattage, and tolerance resistor should I buy? Or is this even possible? Thanks

tblake said:

When I tried a 10ohm (1/2 watt), the high beam indicator went out and worked perfectly. However, about 10 seconds after being plugged in, the resistor burnt up. So I connected two 10ohm resistors in parallel. Worked! then Poof, let the smoke out.
All I know......

-Stock headlight wattage is 65w
-Battery/Charging system runs at 12.6v-14v

What value, wattage, and tolerance resistor should I buy? Or is this even possible? Thanks

Click to expand...

The power dissipated in the resistor is V²/R, so your 10ohm resistor across a conservative 12 volts was dissipating 12x12/10 = 14.4 watts.

I'm amazed the 1/2 watt resistors lasted long enough to see that it worked.

You'll either need to parallel some low watt resistors to get 10 ohms, or get a single high wattage resistor. In either case they will get very hot so you'll need to be carefull about how and where you locate them. Some power resistors can be mounted to a heatsink which might be the way to go.

It would be nice to know the real reason for the problem. I kinda doubt the highbeam light is supposed to light up if bulb fails, and certinly not dimly light up.

Are all the connections and grounds you made on the HID setup good?

You might want to see if a resistance higher then 10 ohms will work. At 15v (closer to what the running voltage will be) a 10 ohm resistor will dissapate a whopping 22.5 watts. Thats alot of wasted power and as gecko said, will be very hot.

tblake said:

When I tried a 10ohm (1/2 watt), the high beam indicator went out and worked perfectly. However, about 10 seconds after being plugged in, the resistor burnt up.

Click to expand...

Was the engine running when the resistor burned out?

I always wondered what the I²T rating of a resistor is! Some projects on this site can be made simpler if you're allowed to temporarily overstress parts.

Thanks.

Andy1845c said:

It would be nice to know the real reason for the problem. I kinda doubt the highbeam light is supposed to light up if bulb fails, and certinly not dimly light up.

Are all the connections and grounds you made on the HID setup good?

You might want to see if a resistance higher then 10 ohms will work. At 15v (closer to what the running voltage will be) a 10 ohm resistor will dissapate a whopping 22.5 watts. Thats alot of wasted power and as gecko said, will be very hot.

Click to expand...

Ok, you caught me. My grounds are good, and all my HID connections are good. My High beam indicator only stays on if I turn my fog lights on.

Here is a copy of the wiring diagram for my car's headlight circuit. I hope someone can help me out with this....

**broken link removed**

A little background. When I bought the car I inserted a resistor into the connector for the DRL ambient light sensor. I also unplugged the DRL diode to bypass the DRL's and automatic headlights. This has worked flawlessly for the past 2 years.

Another problem I had was with my fog light switch. The little yellow indicator bulb burnt out. It was a 12v regular incondescant bulb. My solution was to replace it with an LED and a 1k Ohm resistor wired in parallel.

I think the LED and resistor in the switch is whats causing my problem because I have looked over the wiring diagram and it looks as the indicator uses the high beam circuit as a ground. Then when high beams are turned on, there is no potential difference so the fog lights shut off.

How can I modify this circuit in order to make my high beam indicator stay off? And if I could get my fogs to stay on with high beams on, that would be great too.

Thanks!

Yes the engine was running. It was almost instantanous. I turned the car on, flipped the headlights on, and the resistor went poof, and the smell.......

Do you guys think five 100 ohm resistors in parallel would work?

And a couple pictures for you viewing pleasure....

**broken link removed**

**broken link removed**

Thanks for all the help so far!

tblake said:

Yes the engine was running. It was almost instantanous. I turned the car on, flipped the headlights on, and the resistor went poof, and the smell.......

Do you guys think five 100 ohm resistors in parallel would work?

Click to expand...

No, all five resistors would 'poof' just as instantly.

Notice that the old headlamp was 65W, so you need a 65W load to fool the system that the bulb hasn't gone - and it has to be able to dissipate 65W safely.

You 'may' get away with a smaller load, but you would need to experiment to find out - keeping with the car theme, try an indicator bulb, and if that's OK try an interior light bulb.

But you don't want anything in multiple digits of ohms.

I am by no means a expert, but I am thinking you need to add a ground for the fog light indicater lamp so that it dosn't try and ground itself though the high beam indicater lamp.

Maybe one of the resident experts can chime in. That would be alot simpler then the resistor.

Do a search on making the fog lights stay on with the high beams. I am pretty sure that is a common mod for Grand Prixs'. I am pretty sure I have seen articals online about doing it.

Yeah, your right, it is a common mod. The fog lamp relay is grounded with the high beam circuit. This wire needs to be cut, and relay grounded. Then te switch internally needs to be modded too. Its just too cold right now. Maybe I will live with it untill it warms up.

Besides the resistor idea seems expensive.....

Nigel Goodwin, could you ellaborate on the interior bulb idea?

Thanks for the help guys.

He's talking about connecting a smaller 5W bulb in place of the resistor.