How To Give Headlights Half Power?

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Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=35708
Printed Date: May 20, 2024 at 5:26 PM

Topic: How To Give Headlights Half Power?

Posted By: Coomer
Subject: How To Give Headlights Half Power?
Date Posted: July 16, 2004 at 4:22 PM

Hi,
In my Celica, There are four headlight assemblies. The two outside ones are for the low beam headlights, while the two inner ones are for the high beam headlights. Now what I want to do is to make my high beam headlight bulbs run at reduced power when my low beams are on, so that the headlights light up partially, but not enough to blind people like high beams do.

Here's an example of how it could kind of look:
posted_image

I did that, however, by drilling holes in the high beam assemblies and inserting a 194 bulb in a socket into there...it looked really bad most of the time...it just looks good in that picture.

So here's what I'm thinking...I know how the relays would have to work for this. I've already got my low beams set up on relays so that I have larger gauge wire providing power and ground to them, so getting the +12 volts when low beams are on to the relays below won't be a problem.

Here's my diagram of what I've got so far.
posted_image

Now, I'm not sure what to replace the question marks with in the diagram, so that I can reduce power going to the high beam bulbs. I was thinking that I'd need some sort of resistor, but I don't know if that's correct. If so, what kind(wattage and ohms) resistor do I need?

Oh yeah, I forgot to display the wires in the diagram, but there will still be the high beam wires connecting directly to the high beams, so the high beams will still go to full brightness when they're switched on.

Any help would be greatly appreciated. posted_image

Replies:

Posted By: xetmes
Date Posted: July 16, 2004 at 6:06 PM

usually what is used in daytime running light setups is a high power 1 ohm resistor, if your high beams are 75 Watts a 1 ohm resistor will put it around 30W output, but the power will be around 15W in the resistor. You need to use a power resistor probably at least a 20W one.

What is the wattage of the high beams? I have some 1 ohm 20W resistors I could mail to you for a few bucks if you want...

Posted By: Coomer
Date Posted: July 16, 2004 at 6:25 PM

My high beams are 65 watts. Do the resistors require any sort of diode between the resistor and the headlight, so that they don't get damaged from the full power when the high beam lights are on?

I'm interested in buying the resistors from you, as I need them soon. I'm hoping to have this done by the Celica meet on the 24th. posted_image

So I'll give you a few bucks for them if that's cool. I could pay you with Paypal. Just let me know.

Thanks,
Christian Coomer

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Posted By: xetmes
Date Posted: July 16, 2004 at 6:43 PM

65 watts would be fine then.

no diode is needed with the resistors, but i would put some diodes on those relays.

the reason no diode or anything is needed on the resistor is because if the high and low beams are on both sides of the resistor are at 12V and no current will move in the resistor.

Actually you really dont even need 2 relays, at 65 watts its only around 5 A each light, combined wouldnt really be more than 15A, 1 relay is plenty... would make the wiring easier, Just use 2 resistors and branch from a singal relay.

If you want ill send them, but I cant ship till Monday so just let me know, ill ship it in the mail, the faster service so it doesnt take forever to get to ya...

Posted By: Coomer
Date Posted: July 16, 2004 at 6:50 PM

Oh ok, that makes sense about the diodes. So terminal 87 would be split, and then on each wire coming from the terminal, the resistor would be installed?

And is it alright if I PM you about the resistors on Sunday? I'm going to see if I can find them anywhere in town.

Thanks!

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Posted By: Mad Scientists
Date Posted: July 18, 2004 at 5:16 PM

If you sit down and think about it for a bit, you could probably figure out a way to use a relay or two to have the headlights wired in series for half power, and parallel for full power high beams.

Regards,

Jim