Halogen Headlights

My 2007 has halogen headlamps while my 2004 has HID. I notice a big difference in lighting performance between the two (2004 is much better), especially since when I turn on the 2007 high beams, the low beams turn off.

Can anyone think of any technical reason why it would be a bad idea to have both low and high beams on at the same time (i.e., overheating the bulb?)

The Mustang headlamps leave the low beams on when the high beams are activated, so this provides a much better light pattern. The Highlander has separate high beam bulbs; low remains on when high is activated.

 

Referring to the wiring diagram, the DIM relay switches 12V between the low beam filaments and the high beam filaments. So what I did was to pry out the DIM relay and use a paper clip as a stiff wire to short together terminals 3 and 4 on the base of the relay. (3 is connected to the 12VDC source, and 4 connects to the low beam filaments).

If you wish to follow suit, use your ohmmeter to find the two terminals that show ~0 ohms resistance when the relay is inactive i.e., no power applied to the coil terminals. Those will be terminals 3 and 4.

When the relay is plugged back into the socket and the headlights are turned on, the low beams will always be powered up now, regardless of the DIM relay position.

I'm guessing that the current flow to the low beams is around 8A (assuming 2x 55W bulbs) so I clamped the shorting wire to the two relay pins very tightly, using long-nose pliers. It works quite well and of course the mod can be easily removed if desired.

 

Good point. The HEAD MAIN fuse is rated at 40A so I will assume that the wiring between that fuse and the H-LP relay will carry that current.

The H-LP relay is located next to the DIM relay, so the wire connecting the two should be very short, maybe two or three inches long. That is the only wire to worry about, regarding excessive current. The wires from the DIM relay to the headlight filaments will not be carrying more current than normal.

I want to have the low beams on all the time that the headlight switch is on, and be able to switch on the high beams (when there's no oncoming traffic) while leaving the low beams on.

 

Yes, I am also concerned about that.

 

More like 110+ degrees F in the summer day here in southern AZ, but there's no need to turn on the lights in the day. I agree that summer night temps can range into the low 80's F.

Well, I came up with what I thought was a good and simple approach regarding how to make the low beams stay on. I just wasn't sure whether this was a good idea since the car was not designed that way...

But I am going to try it for a while and see if anything happens. If you read in the paper about a Prius in southern AZ catching on fire due to its headlights, you'll know how that happened...

 

Hi ZC1,

My question and recommended approach relate solely to Prius halogen headlights.

This is not an issue with the Prius HID lights because the top of the light pattern moves up when you select high beams, while the bottom of the pattern remains unchanged. (The same bulb produces both high and low beams.)

I agree that HID lights should not be turned off and then back on quickly.

 

I don't think the wiring diagram was posted in this string. You can obtain that at techinfo.toyota.com which is a subscription website that provides Toyota factory repair manual info.

 

Yes, the DIM relay is located in the main relay/fuse box near the inverter. No problem after four years of use.