Hot Rods H4 headlights

Probably a dumb question but can somebody explain how the double filament headlight bulb works . when switching to hi beam does the low beam stay on and hi beam added or does the low beam go off and the hi beam come on . I’ve asked a few people and get different answers

 

You can fire up both filaments at the same time.
I can turn on both filaments with my center headlight horn switch on my 37. Ive run them on for a good while when I’m having night time viewing difficulties. Much brighter. But I would imagine the extra heat and current through the bulbs will effect the length of endurance.

 

Usually the low beam goes off when the high beam comes on, but as Petejoe says, you can wire them up to come on, and stay on at the same time. Most, if not all high beam switches are made to turn off the low beam when switching on the high beam. The way to bypass that is to not run the low beam wire through the high beam switch. That way when you press the high beam switch, the low beam will stay on. Pretty easy really. As Petejoe says, heat might be a problem, so run heavy wire, and bigger fuses.

 

They are supposed to run separately. As mentioned, running both at the same time will shorten their life because of excess heat in the lamp. One other thing bears mentioning. Running both the high and low beams at once reduces the effectiveness of your high beams because of how the human eye works. While it appears to be 'better' light, it actually reduces the distance you can see.

 

As said, one or the other.
Excess heat will burn the reflector over time so the surface turns matt, large headlights may handle it okay but small ones are likely to overheat and kill themselves over time.
It's a known issue with 100W "rally" H4 lamps even when only one filament is in use - I'm guessing they may be called off road lamps instead of rally on your side of the Atlantic, high power lamps not really legal on road. Modern plastic reflectors are obviously more sensitive than older metal ones, but they all suffer from it.

 

H-4 is a direct replacement for a standard Dual (hi-low) sealed beam. They do and should work the same as a sealed beam.

I'd have to think that running both elements at yhe same time would indeed generate too much heat along with the high amp draw.
I ran 7 inch Cibies with 55/100 H-4 bulbs in my 48 for years untill the reflectors got cloudy. they threw a great light on low or high beam when they were in good shape.




















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I just run Cessna landing light bulbs for bright lights. I like to see 2 miles down the road like it’s day time.

 

The Koito replacement version was on super clearance last year, the whole kit could be had at online Toyota dealers for $18-$25.......I bought a few .

 

I once did a lighting upgrade in an OT early 2000’s Toyota Tarago soccer-mom van.

Forgive me for owning anything so soul-less.

Fitted relays, then swapped the low-wattage H4 bulbs for 130/90W bulbs. Those tiny reflectors now lit up the road like daylight.

I didn’t realise Toyota wired them so low and high beam operated at the same time. 210W, or 17.5A. The power supplies to the bulbs were fine, as they were separate (11A in one wire, 7.5A in the other). The problem was the earth pin in a H4 bulb is common. That poor pin copped 17.5A. My relayed wiring was fine, but it would melt the common earth pin inside the bulb.

One is not readily forgiven when SWMBO loses headlights 60 miles out of town, in the backwoods, with four kids in the car.

cheers,
Harv

 

Painless has a kit for hi and lo simultaneous lights; right size wires, fuse, and relay. Been using kit for 25+ yrs.

 

Ran both hi and low together on one of my old 6volt Harleys, kept burning them out...finally figured out why after the third time.