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):
- Pin 30 - On the pigtail, this is the LARGE RED lead. This wire will be connected to the horn relay to provide the main power for the headlights. Make sure this wire has a GOOD connection to an ALWAYS ON power source. This will help your headlights be as bright as possible.
- Pin 85 - On the pigtail, this is the GREEN lead. This will be be connected to the firewall side of the split (which I haven't told you about yet) in the green/tan headlight circuit from the wiring harness. This is used to energize the relay and complete the headlight circuit. When the headlights are turned on inside the car, the green or tan headlight power wire is energized, depending on whether you're using hi or lo beams, and this activates the relay. When the headlights are turned off, the green or tan wire has no power and switches the relay off.
- Pin 86 - On the pigtail, this is the black lead. This will be connected to ground. I'm going to use the same ground point I have to headlights run to.
- Pin 87a - On the pigtail this is a YELLOW lead. I trimmed this off of my pigtail because I won't be using this pin. On the Bosch relay I bought, a 5 pin relay, pin 87a is normally active when the relay is inactive, so it wasn't useful for my purpose. If I had wanted something to turn on when the headlights are off, this might have been useful.
- Pin 87 - On the pigtail this is a WHITE lead. This is used to power the headlights and is only active when the relay is active. It's the same large size as the RED wire since the relay just relays the power from the red wire to the white wire when the relay is activated. Making it smaller would have just lead to wiring meltdown.
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.
- Connect the firewall side of the original harness's green wire to one relay pigtail's green wire (pin 85), or run a wire with a female connector to the relay pin. Label this relay (in your head or actually on the relay) as the low beam relay.
- Connect the firewall side of the original harness's tan wire to the other relay pigtail's green wire (pin 85), or run a wire wtih a female connector to the relay pin. Label this (in your head or actually on the relay) as the high beam relay.
* Note - You may find different sources telling you different things about how to use pins 85 and 86 on the relay;it really doesn't make any different which one is which. Either pin cab be used for ground or power for the activation lead. They can be used interchangeably as long as their used consistently. In this install, if you use pin 85 for the relay activation power, USE pin 85 FOR THE RELAY ACTIVATION POWER ON BOTH RELAYS.
- Connect the headlight side of the cut green wire to the white wire (Pin 87) on the low beam relay.
- Connect the headlight side of the cut tab wire to the white wire (pin 87) on the high beam relay.
- Connect the RED leads (pin 30) from BOTH relays to the horn relay or other full time 12V source.
You may want to consider putting a 30amp fuse, or fusible link, on this part of the circuit too. On mine, I'm soldering both of the red wires to one side of a butt connector and then soldering another wire of the same gauge (10 gauge) to the other end of the butt connector and then running that wire to the horn relay. If you don't want to use the horn relay as your power source, pick another distribution point that has a GOOD and constant 12 volt source of power.
- Connect the BLACK leads (pin 86) from BOTH relays together and then run them to wherever your headlights are grounded to. I'm soldering these up using the same procedure I did with the red wires except that I'm not putting a fuse in the ground portion of this circuit; it's not necessary.
* Note - You may find different sources telling you different things about how to use pins 85 and 86 on the relay;it really doesn't make any different which one is which. Either pin cab be used for ground or power for the activation lead. They can be used interchangeably as long as their used consistently. In this install, if you use pin 86 for the relay ground, USE pin 86 FOR THE RELAY GROUND ON BOTH RELAYS.
It's a bit hard to see in this picture, but both black wires from the relay pigtails are soldered together and connected to the black wire running through the relay mounting baseplate.
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.