How To Wire Relays for H4 Headlights -- help please

[Rich911E]

I have been following the threads on the H4s and noticed that many people advocate the use of relays with the H4 headlights to avoid overloading the stock headlight switch. I was wondering if someone could provide some detailed instructions on how to do this.

I put the H4s in my 1969 911 and had a weird electrical problem one night which blew the voltage regulator and seemed to be happen just after I adjusted the brightness of the dash lights. It seems OK since the new voltage regulator, but I would like to have the relay system for some extra insurance. I have a sneaking suspicion this will raise its head again on some lonely backroad.

Could someone sketch out a wiring diagram and take a couple of pictures of how this is done. (NOTE: I am a complete novice at electrical systems. Much beyond "Up = on and Down = off" and I am lost. )

Thanks very much in advance,

Rich Murphy

[Wil Ferch]

Rich:
Off line....get me your fax number and I'll send you info how i did my 85 with the Marcus Sucro relay kit. Other kits will be done the same way.
-- Wil Ferch

[jwill911]

I was going to say that... But mine is at home so I can't fax it now. But if you don't have a fax machine I can scan mine later tonight and email it to you.

John

[Jeff]

Wil or John,

Any way you can post it here. I don't have access to a fax?

[Rich911E]

Wow, that was fast -- thanks.

My fax number is 858-452-4945

Thanks again.

Rich

[Rich911E]

I checked my nearby fax, but nothing came through. Please resend. If you are having difficulty with this number, another fax number at work here is 858-597-0237.

Thanks again,

Rich

[kretzj]

I am in Tiawan at the moment so I don't have the layout in front of me. I do have a picture of my relays on my '72 911 with H4s.

Jon

[Rich911E]

sorry, the faxes never came through, but the picture was a great help. I never thought of mounting the relays inside the headlight bucket. That should make wiring a breeze.

Regarding the power source, did you take it straight from the battery or some other power supply on the fuse panel?

Thanks


Rich

[kretzj]

Rich,

The red wire that goes out the side is connected straight to the battery. Since my car is a '72 with a battery on each side, the hot lead was easily connected. If you look closely, the hot wire runs to a fuse then the relays.

Jon

[Wil Ferch]

Guys:

OK...I'm not at work, I'm at home, so I can't fax and doing so wouldn't help other members on this list. Let's try it this way, but be careful with text.... !!

A relay has (typically) 4 labelled connections... 87 and 30 can be considered the high current "contacts" that will carry the headlight current load ( bi-directional, doesn't matter which is "in" and "out") ...the other two... 85 and 86 activate the low voltage coil which in turn will open/close the 87/30 contacts. Look at the relay cube and you'll find these. The cube "holder" will have the wires coming out of it that need to match-up to these numbers.

So...a big fat lead comes from a new ring connector on the positive side of the battery and leads to 87 of one relay ( optional, you may want to install an in-line fuse here). Jumper from 87 of one relay holder to 87 of the other holder ( you want at least two relays, one for hi and one for low beam). Jumper 86 to 86. Take one of these 86's also to "ground". Or have each 86 go to ground individually...your choice.

On the first relay, wire from 30 goes to the topside of the existing fuse box where the low beam circuit is. This most likely presently has a yellow wire attached. Remove yellow wire, and connect yellow wire to the relay wire on 85. Wire 86 is to ground, remember.. Your previous yellow wire WAS handling all the headlight current. Now it simply activates the relay coils ( that IN TURN) close the contacts that really handle the headlight current. Got that? The headlight switch will now see MUCH lower current and will live longer.

Do the same for the other, high beam circuit. Only that probably is a white wire ( not yellow) that is presently activating your high beams...this white wire will go to the other realy's 85 pigtail lead. The output of this new 30 will land on the top of the high beam circuit in the fuse box where the white wire, (now removed) had been.

That's basically it...except you must first check your own wiring to verify that you had a yellow wire leading to low, and a white wire leading to hi. Adjust this text accordingly.

Summary...New yellow goes to 85 of one relay..new white goes to 85 of the other relay. Output wire from the first relay at point 30, goes to top of fuse box on low-beam circuit ( where yellow WAS)..and output wire from 30 of the second relay goes to top of fuse box where white WAS. Both 86's go to ground. You're done.

If things blow up...you're on your own ...but this is correct for my car and most other Porsches of those model years ( mine's an 85) that haven't been electrically modified.

BTW..I used a flying fuse in the main power from the battery to the first 87...and used 14-12 gauge wire and a 25A fuse. I retained the original headlight power ( 60/55W) and therfore didn't change the two 8A fuses for low beam, nor the two 8A fuses for high beam. These 8A fuses are marginal ( barely) when using 100 W bulbs, so go next size up ( 16A) when at / over 100W. Beyond 100W, I wouldn't trust the existing wire size from the fuse box to the headlights, and would do upgrades there, too.


Someone else..pleae verify...I'm quite sure this is correct, but.....

---Wil Ferch

[Rich911E]

Jon and Wil:

Thanks for the detailed information on the wiring. Thanks to my three year old and six month old, I didn't get a chance to do this over the weekend, but it will be project for some evening this week. I will redraw the wiring harness and post it here in color for future reference or maybe draft it as a tech article for everyone to review and comment.

Thanks again for your help. The information makes this a lot more clear, especially for a hopeless electrical person like me.

Rich

[Rich911E]

It worked! An electrical project that didn't end up with smoking wires and blown fuses.

I will post the details soon, but I used two relays in each headlight bucket (one for high beam and one for low beam for each headlight) and ran the wire from the battery directly with two fusible links with ten amp fuses. The lights are WAY brighter than they were before.

I'll draw the wiring diagram and post a couple of pictures tomorrow or the next day.

Thanks again for everyone's help. Now I can try some backroads at night without worrying.

Rich

[reed930]

Uh oh. I just purchased a set of H4s for my '86 930. I thought it was a simple swap. Is there more needed? I ordered the kit from Pelican and did not receive any relays. I'm sure glad I read this thread before taking the old unit apart. This sounds more complicated than I first thought. Any help would be appreciated.

Chris

[nostatic]

I bought one of these:

http://members.rennlist.com/msucro1/relaykit.htm

I haven't installed it yet, but it looks to be good quality and very easy to hook up.

[steve911]

Marcus' relay kit is top-notch and everything is clearly labeled along with a complete instruction sheet. A VERY easy install.

just a satisfied client