Headlight Upgrade, Installing a Light Harness

[bavbob]

I have installed an upgraded light harness on a bunch of my cars so decided to take on the Bavaria. The harness allows power directly from the battery/alternator rather than running power through the switch/stalk. Each harness has two female connectors, one to each H4 light, two relays each fused (30 amps), and one male connector that is connected to one of the two original female connectors that went to an H4 light, doesn't matter which. It also has 2 lines for power and 2 lines for ground.

The premise is simple, turn on the lights, power goes to the relays via the connection between the harness male connector and the chosen original H4 female connector. This opens the relays that are connected directly to the battery and to each H4 light.

The set up is simple but where to place the relays and run the wires takes logistical planning to make it inconspicuous. I went through this with the Bav so thought I would share. I started on the drivers side, removed the cover and light bucket. This is where the relays will be mounted and most of the wiring.

There is a hole behind the left light bucket as seen here. On the other side it is along the battery. I ran the 2 power lines to the battery through this hole, around the side of the battery (between battery and can relays) and to the positive cable (two red wires as shown).

I mounted the relays as shown here through a small hole which is near the radiator support bracket and was already there, I assume it is factory . The setup I used, comes with relays joined by a mounting bracket that has a single hole that fits an M6 bolt.

The male connector from the harness plugs into to the pulled female three-pronged connector from the left H4 headlight. One of the three-pronged female connectors from the harness plugs back into the H4 headlight, ground wire to the usual location where the sidemarker light is ground to.

I ran the wiring for the passenger light below the radiator and through this front cowl that has an opening on both sides of the car, then behind the right light bucket. This line has only a three-pronged female connector that plugs in to the H4 light and a ground wire that goes to the right sidemarker ground. The old female connector from the H4 light gets taped off and just sits behind the light bucket. Done.

Lights are substantially brighter. Simple upgrade. Hope this helps someone else. Assume it can be applied to the E9 as well (that's next).

 

[Stevehose]

Well done, this is an important upgrade to do, my lights are much brighter (and safer) as well. I used the 3rd relay slot for a Hella can relay:

https://e9coupe.com/forum/threads/help-with-headlight-driving-light-rewire-project.7959/

 

[bavbob]

I was not a believer until I bought a set of Koito's for our Mustang and it came with a harness. My son took the Mustang out and came back and said quote "Holy shit what ja do to the lights, I can see everything!" I did not ask about how he saw before I did the upgrade.

 

[DaveBeddows]

You didn't mention fuses. It is a good idea to put fuses between the hot leads from the battery and the relays. It is possible for an internal relay failure to cause a fire in an unfused circuit. If this happens chances are the hots leads will burn to open circuit and as they are not near anything flammable they won't cause a fire. This was the case in pre '74 cars with internal relay failures on the bank next to the battery.

I wrote an article for the club magazines and forums 26 years ago about this. The E3 and 2002 models from 1974 - 1976 were vulnerable to nasty car fires due to internal high beam relay failures. If you have ever seen a '74 or later fire destroyed 2002 or E3 it is very likely the cause was the high beam relay.

The early high beam relays had a design flaw in that the contact arm was held into it's pivot by the torsion return spring. If that spring fatigued it would break and the spring metal and/or pivot arm would drop or vibrate down into the base of the relay were they could bridge the gap between the unfused 12 Volts and Ground. BMW later discontinued the original relays with a newer model that was not vulnerable to an internal short. Did they do this because they knew of the issue? Who knows. I never heard of a service bulletin for it. It is most likely the same relay was used in many different applications and its weakness caused it to be discontinued.

I can find and post my article if anyone is interested. The E9 didn't appear to be as vulnerable to the same weakness. I never did a full rewire or examine the harness layout for a E9 so I can't be sure. I've only done harness design and complete rewires on E3, 2002, 507 & pre-war 327/328's.

 

[Stevehose]

I fused mine in a separate project, with a small box mounted on the firewall.

 

[bavbob]

See the second line of my OP, harness comes fused.

 

[Drew Gregg]

Rob--Inquiring minds will want to know where to get the harness. These cars are not driven much at night, but having the best lighting when they are driven is a safe feature. Sealed beams with factory wiring are 1939 technology. That was the year sealed headlights were made standard on USA vehicles.