Upgrading your headlights with Bosch Relays for brighter lights

As part of the wiring upgrades on my car, I'm also installing a set of headlight relays to take some of the load off of the OEM wiring setup so that the headlights will run brighter. This is accomplished with relays, which use the original headlight power wires as switching leads only. The relays get their voltage directly from the battery and provide it to the headlights without having to run through the old wiring harness. Since activating the relay is a really low voltage, low draw circuit, there's lots of power left for stuff run off of the fuse panel.

I'm using Bosch 30amp relays for the switching relays along with relay pigtails that I picked up at NAPA. The pigtails were actually more expensive than the relays themselves, but they will save me a lot of effort when completing the wiring.

Some time ago on Steve's Nova Site, someone suggested mounting the relays in an old voltage regular casing, if you're using an internally regulated alterator, is a good way to hide the relays in order to clean the installation up. I thought this was a great idea, so I'm proceeding that way.

Here's what the voltage regular looked like installed in the car before I tore the car down for its restification.

Here's a picture showing the voltage regulator torn apart.

In order to tear the voltage regulator apart, I had to drill out the six rivets that were holding it together. Two rivets held the top cover onto the baseplate and 4 others held the circuit board and voltage regulator wiring harness connector pins to the baseplate. I used a 1/8" drill bit to quickly destroy the rivets and not tear up the case. The circuit board that once was used to regulate voltage on the old style alternators is now garbage. It's not needed anymore.

Left behind is a nicely sized metal box that's perfect for holding 2 Bosch relays.

I stripped all of the old paint off of the regulator housing, sanded it down a bit, gave it a quick etching with some paint prep acid, and then gave the inside, outside, top, and bottom of the case a coat of gloss black paint to match the paint on the core support it'll mount to. One other modification I made to the housing was to cut a small slot in the baseplate to give the wires a place to exit. I split a piece of 1/8" tubing to use as a grommet around this hole. That will keep the wiring from getting sliced up by thes sharp metal edge of the opening.

The relays I purchased required a small modification to fit nicely into the regulator housing. They had plastic mounting tabs molded into their cases which I trimmed off with my dremel tool in order to make them fit easily into the regulator housing.. I'm going to epoxy the relays to the regulator housing baseplate to keep them from moving around and wearing down the wire insulators.

In this picture you can see the relays before and after my modification with the wiring pigtails attached. The bottom one is an unaltered relay. The top one has the mounting tab trimmed off.

Here is a picture of the pins on the relay and a wiring schematic showing the circuits in the relay.


Now that I've got the prep work done, it's time to get started with the wiring details.

The relays I chose, each have 5 leads coming out of them. Only 4 of these I need to use right now. These leads are labeled as follows (there are labels and a schematic molded into the relay showing which pin is which and how it should be wired):

The power leads for the headlights in my 67's OEM harness are colored tan (tan) for the high beam circuit and light green for the low beam circuit. I could be wrong regarding the green being high beam and the tan being low beam, but it doesn't make any difference in the wiring since which wire is active at any given time is controlled by the dimmer switch inside the car. I'm absolutely correct about those two wires being the headlight power leads though.

The ground connections for the headlights, using the OEM setup, is provided by two small black wires with ring terminals that connect to the core support. I didn't like it done this way, since I couldn't easily/cleanly guarantee that my core support has a decent ground anymore due to the fact that I didn't want to remove any my new paint job. To fix this, I lengthened the original ground wires and I'm now running them directly to the battery to ensure a good ground. This isn't necessary to do as part of this upgrade, but since I have the whole car's front wiring harnesses torn apart, it's not a big deal to do now.

Here's a diagram showing the circuits we'll be wiring.

The first thing you'll need to do is cut the green and tan headlight power wires. This divides the circuit so that you can splice the relays in between the cuts. I'd cut them as close to your relay mounting point as you can. This should save you the trouble of having to splice in extra lengths of wire to complete the circuits.

These next two pictures show where I made my cuts. I twisted the ends together to give myself an idea of how much wire I'd need to cut off so that I didn't cut myself short or leave too much wire that won't bundle back up properly when I wrap it back up with wiring harness tape.

This shot shows the wires trimmed and crimped together using a butt connector. After this, I soldered the connections and covered them with shrink tubing.

Of the two relays you're connecting up, one will be used to power the low beam headlight circuit. The other will be used to power the high beam headlight circuit. It doesn't matter which relay you use for which as long as the green wire goes to pin 85 of one of the relays and the tan wire goes to pin 85 on the other relay.

Before bolting the cover back on the mounting plate, I used some quick set epoxy on the back of the relays to keep them solidly in place so that the connections didn't wear and so that they didn't rattle around inside a small metal box. That rattling would have driven me insane. I also made sure than any metal edges the wiring passed over were covered so that they couldn't wear through the wires.

Here's the old voltage regulator housing mounted back up to the core support. Only we know that this isn't a factory install, but the factory never made anything this pretty.

Pat yourself on the back, you're done. It's really not that hard when you take the time to think about it first. Your headlights will thank you with MUCH brighter nighttime operation.