Motorcycle H4 Headlight Relay Kit Instruction Sheet

Positive Ground H4 Relay Kit - read here first:

External Modulators: Make sure you connect any headlight modulator directly to the bulb. The Relay Kit connects to the modulator.

Headlight Glass Cleaning: Now is the time to clean your headlight lens if it looks a bit unclear. Sometimes you can clean it through the bulb opening but if you can, remove the lens and clean it well. They tend to get a film of dust and whatever after long periods of time. Also blow out all dust you can find in the headlight and clean everything!

Description: The kit plugs into the existing headlight bulb(s) and socket up front, and attaches to the bike’s battery posts at the other end. The main positive (red) wire nearest the fuseholder on the kit should be connected directly to the bike battery’s positive post. It can also be attached to the main positive output terminal of the bike’s alternator.The main ground (black) wire is attached to the battery negative post, or to any good bike ground. Read these instructions all the way through before beginning installation.

Preparation: First remove the black negative wire(s) from the bike’s battery to avoid any problems. Make sure the wire(s) will not touch the battery post during your work. You will need to gain access to the rear of the headlight bulb(s), but you will not have to remove the bulb(s). This could involve removing the back of the headlight housing or some fairing parts. See your bike manual.

Do not install a fuse in the fuse holder of the kit yet. You will be connecting to the bike’s battery and you don’t want the red (hot) wire to cause a problem when it’s connected. Only replace this fuse when you are finished and have double checked your work.

Installation: Unplug the existing H4 headlight socket(s) from the headlight bulb(s) by carefully pulling it back from the bulb until it comes off. Do not force it if it’s stuck. You might have to rock it a bit to get it loosened enough to come off.

You now have two choices to connect to your bike headlight’s low and high beam wires:

1 - H4 Coupler Option:

If you are using the H4 Coupler to plug into your bike’s H4 Socket, make sure it’s tied up and taped to avoid shorts.  You might also want to re-read the pros and cons of each connection method on the Main H4 Page.

Plug the H4 Coupler from the kit into the bike’s H4 Socket you just pulled off the bulb. If you have H4 Dual headlights, you will plug the H4 Coupler into only one of the bike’s H4 Sockets. The other will not be used so tape and tie-wrap it up out of the way. Make sure you insulate the unused H4 Socket against possible shorts.

Now plug the kit’s female H4 bulb socket(s) onto the bulb(s). Make sure any rubber bulb shield is back in position properly.

You can now skip the next section and go to Securing the Relays below.

2 - Posi-Lock Connector Option:

First you should determine which wires are Hi and which are Lo beam on your bike’s old H4 Socket, before cutting those wires off. On my Kits, HI beam is white and LO beam is yellow. Wire colors vary from make to make but BMWs use these colors. Japanese bike headlight wire colors are often the opposite. You can ID H4 wires by their position on the socket as shown below.

You might want to do one wire at a time to avoid mixing up the wires. You will also have to strip 3/8 inch of insulation from each of those wires. See the photo below to identify the Hi and Lo beam wires on an H4 Socket.

First, cut off the H4 Coupler (NOT THE SOCKET!) on the Kit close to the Coupler, and strip 3/8 inch of insulation from both the yellow and white wires. Then install a Posi-Lock onto each wire. See here for Posi-Lock instructions.

If you have Dual H4 Headlights, you will be using the wires to only one of your bike’s H4 Sockets. The other can be totally removed from the system at this time.

Now install the other ends of the Posi-Locks onto the two POWER wires that went to your bike’s old H4 Socket. Make sure you connect the high beam wire to the Kit’s white high beam wire, and low beam wire to the Kit’s yellow low beam wire. You will not use the old ground wire that went to the bike’s old H4 Socket. Cut it off too, and tape and tie-wrap it up so it won’t cause a short later.

If you do get your high and low beam wires reversed, you can remove and re-attach the Posi-Locks to the proper wires later, with no problem.

Plug the Kit’s female H4 bulb socket(s) onto the bulb(s). Make sure any rubber bulb shield is back in position properly.H4_socket_wiring2

H4 Socket Wiring:

To the right is a photo of how to wire the H4 socket, for those with H4 Kits with wires not yet installed for easy of insertion in a headlight shell grommet. The terminals just push in and should click in place when fully inserted. Make sure you run the wires through the grommets into the headlight shell before plugging in the terminals!.

Securing the Relays:

H4S Kit: Use a tie-wrap to secure the relays so that they won’t bang around in the headlight shell. You can tie them to existing wires or any solid mount inside the headlight shell.

H4F Kit: You can secure the relays with a tie-wrap onto the fairing up out of the way and protected from the weather as much as possible. If possible you can bolt them to an existing bolt or drill and mount them with a nut and bolt wherever it is handy to do so.

H4W Kit: When securing the relays under the front of the tank, you have to be extra careful that neither the relays nor the wiring will be pinched or banged by the fork tubes or any other moving parts of the front end.

All Kits: Tie-wrap the wiring carefully behind the headlight so it will not be disturbed. Be very careful around any part of the steering that moves. The fork tubes should not pinch or pull any wires when the forks are moved all the way to either side.

Routing the Kit’s Main Power Wires:

Route the Kit’s main wiring back towards the battery. You might want to remove your gas tank, or you could carefully push the wiring up under the tank into place if you have room. Usually you can follow along next to the existing wiring on the bike and tie-wrap everything carefully into place.

Make sure that no wiring will be squeezed, pinched, or rubbed in any way. Take your time here and do it right.

Battery Hookup:

The wiring around the battery area should be tied up neatly with the fuse holder easily accessible. Remove the screw holding the wire(s) onto the positive battery terminal. Clean with fine sandpaper and check all existing connections you removed, including the battery post and the screw and nut. The red wire of the kit goes onto the positive terminal of the battery, with any of the existing wires you just removed. Now check and clean the same way with the negative battery post, screw, nut, and wire(s) you removed earlier. Replace these wire(s) together with the kit’s black wire, onto the negative battery post. Alternatively, the black wire terminal can be connected to another good bike ground.

NOTE: The red wire of the Kit can be attached to the bike alternator’s main positive output terminal. This might be a good option on some Japanese bikes which have a main fuse to the battery from the alternator.

Testing:  Go back over all your work carefully, and test first with the ignition on but bike not running, and the Kit’s fuse still out, that you can hear a soft click from each relay when you activate the headlight in both high and low positions. Do not proceed until you hear the clicks. This tells you that the relays are properly connected. Now insert the fuse and check that the headlight is working normally.

Notes: Battery connectors do corrode over time. Special grease is available to avoid this. If you find your battery terminals are covered with some kind of this grease, you must clean and remove all of this material before re-attaching any wires. Then re-apply it if desired, when you’re finished. Make sure any battery terminal shields are not broken, and are properly replaced when finished. Battery connections that are not covered with grease should be removed and cleaned yearly, so don’t avoid this important step. Don’t over tighten connectors, and check the routing and condition of all wiring you see as you go. It is very important on a bike that wiring is not being rubbed or worn between other bike parts, or allowed to hang loosely with movement. The relays are light and tough enough to just hang on the wiring up behind the headlight, or you can tie wrap them to any convenient position close to the headlight. Pay attention that no wiring is pulled or pinched when the handlebars are moved from the full left to full right positions.

Vintage bike installers with the H4 Single Positive Ground Relay Kit:

If you still have the stock headlight socket (non H4), then you will also have to remove it and attach the hot wires from it to the posi-locks on the kit’s switching wires. The red ground wire on the stock bulb socket will not be used and should be taped up out of the way. You must identify your Hi and Lo beam wires either from your wiring diagram, or by testing them before cutting the old socket off.

Installing the Positive Ground H4 Kit is other wise the same as the regular H4 Kit, except the Kit’s main wire colours are reversed. I have ridden a Norton for many years with an H4 conversion running a positive ground on the H4 bulb, and enjoyed long bulb life and a bright headlight.