H4 headlight conversion. . does it require a relay?

Desolas · Post by **Desolas** » Mon Apr 09, 2007 8:40 pm

I'm converting my 72 Superbeetle headlights to modern H4 lamps, the bulbs I bought with the headlight lenses says they are 90/100W. Should I run a relay switch for each lamp, or can the stock wiring harness/fuse wiring handle this much amperage? That's less than 10 amps per lamp so I would assume the stock wiring should be able to handle it as long as it's in good condition. All of my connections are sound and in good condition.

Has anyone tried running them without a relay, can it be done, should it be done?

MNAirHead · Post by **MNAirHead** » Tue Apr 10, 2007 2:16 am

Since they were in the front I ran heavier guage wire.. not sure if it was necessary.. would like to know.

MinamiKotaro · Post by **MinamiKotaro** » Tue Apr 10, 2007 3:55 am

I just plug'n'played them on my '67. That was a couple of years ago and they've worked wonderfully.

Post by **2088 bob** » Tue Apr 10, 2007 10:04 am

If you want to take full advantage of these lights you might want to read the following website and if you decide to go with whats discussed there will definitely be some rewiring involved http://www.madelectrical.com/electrical-tech.shtml

Desolas · Post by **Desolas** » Tue Apr 10, 2007 3:08 pm

Thanks for the input. I am going to do some testing, I will install them without relays and see what the voltage drop is like around the circuit and decide from there. I can also check the current draw, I think at this point I am leaning towards adding some relays just to avoid the voltage drop potential.

Thanks!

Kelley · Post by **Kelley** » Tue Apr 10, 2007 3:19 pm

No relays needed.

Chris V · Post by **Chris V** » Tue Apr 10, 2007 3:57 pm

With 90/100W lamps you should run larger wire and use relays in a factory 12V car...

Post by **2088 bob** » Tue Apr 10, 2007 6:11 pm

like i said if you want to take full advantage of the lights you need to consider rewiring especially with your battery located in the back it will make a difference instead of sending the circuit thru the crummy old headlight switch

Desolas · Post by **Desolas** » Tue Apr 10, 2007 9:47 pm

Alright, I went to work this afternoon and got the lamps installed. One, I don't think they required larger wire to handle the amperage so I used much of my original wire when installing the relays (from the relay to the lamps) before installing I connected the new lights to the original wiring and did some testing. First thing that confused me was my high beams would not work with these lights installed; do modern H4 bulbs have high beams? I've never owned a car newer than 1972.

I found I had a 1.1v voltage drop with the original wiring, and while the lights looked okay they didn't look super bright as I expected. So I installed the relay on one side first and corrected the voltage drop. There is a noticeable difference viewing the car from the front by eye between the bulbs in brightness. The side with the relay appears slightly brighter in daylight; which is kind of a moot statement since I first said I had a voltage drop so you'd expect that.

So long story short; I think it would have been fine without installing relays, installing them was worth the hassle. With the voltage drop I had I kind of find that suspect and wouldn't be surprised that without the relays I might have found I had a bad connection somewhere and ended up with wiring issues later.

I'm still unsure about the high beam issue, if it is a issue. I won't need high beams because of the added brightness but I haven't found any answers by googling if H4's have high beam or not.

Post by **Marc** » Tue Apr 10, 2007 10:14 pm

Power for the headlamps on `71 and newer cars goes through the ignition switch "X" terminal, then to the light switch, then to the hi/lo relay, then to the fuse box where it's split out via 4 fuses to the LH & RH hi and low beam filaments (and H4s do have both). The ideal installation will need TWO relays, downstream of the hi/lo relay, each supplied by a 12GA wire from the battery (independent of the stock B+ wire).

BTW, to the best of my knowledge 90/100s aren't street-legal in most (if not all) states). But with all the fancy super-bright stock lamps coming on high-end cars these days you'll probably never get busted for them provided you aim them correctly - and never blind a cop coming the other way

Post by **2088 bob** » Wed Apr 11, 2007 1:58 am

Marc pretty much nailed that one, only change that i would make, is to go to a 10ga wire as opposed to a 12ga pulled independently from battery but then thats just me........ remember this wire needs a fuse

Desolas · Post by **Desolas** » Wed Apr 11, 2007 9:54 am

When I was first putting this car together I ran a 6AWG lead from the battery to the trunk, with a 40A fuse. This way I've got a nice lead to tap into for stereo, and other accessories. I charge smaller batteries off my car battery and it's easier to plug into the trunk than access the main battery all the time. Was worth the effort, makes life much easier when doing this. I changed the wiring so instead of the headlight switch pulling from my ignition it pulls straight from the battery (it is also fused.) The headlight relay just triggers the new relays for lo/hi beam.

I know 90/100 are not legal; but I've got eye brows on the headlights, and with the lamp adjusted down somewhat it shouldn't be a problem. If they seam "too bright" I'll get a 50-80W and see. I didn't realize they were not legal at the time, I kind of bought randomly. The fixtures look cool but the design is kind of poor so they probably waste a little bit of light as well. I haven't been able to drive it at night yet, but today in daylight in traffic I could see the beam from the projector on the car ahead of me really well....might be kind of bright.

I need to look into this further, I wired the high beam relays today and they are coming on, sending voltage to the lamps, but the lamps just turn off instead of getting brighter. These were some el-cheapo brand x bulbs that came with these kind of cheap lamps so it wouldn't surprise me if it's something with them...gonna buy a extra set of bulbs to keep in the car if one goes out and see what they do with hi beam.

Thanks for your help...it's nice discussing this with people.

MNAirHead · Post by **MNAirHead** » Wed Apr 11, 2007 10:07 am

Interesting setup with the spare battery.. how does it get charged?

Desolas · Post by **Desolas** » Thu Apr 12, 2007 7:29 pm

No, not a spare battery. I have the battery under the seat with a 6AWG lead to the trunk ... I ran a 6AWG lead along side the factory (10awg?) lead so I'd have a more reliable source of battery power in the trunk.

Anyway, some of you will find this amusing. I've been trying to figure out why my high beams won't click on, been going back and forth doing wiring diagnosis, testing relays, chasing grounds and when I clicked my high beam switch the relays just were NOT being energized.

....then I realized I was pulling back on the wiper lever and not the turn signal lever..yeah, sometimes I'm dyslexic apparently. When pulling the correct lever the high beams work just fine..imagine that.

These lights are AWESOME. Not too bright since I've got kind of poorly designed fixtures and the eye brows, but a huge change from the stock bulbs.

Got all the wiring hidden today, very tight install and worth every minute of time spent on it.

Kelley · Post by **Kelley** » Fri Apr 13, 2007 8:44 pm

Pics?