Picture of a Lucas Headlight Switch

Lucas Switch

There are very few companies in the car world that get the ribbing of Lucas Industries.  They are the butt of many an old car guy’s jokes about reliably, safety and burning.  The company was founded in the 1860’s in the UK and produced electrical components for over 100 years for all of the popular British brands.  These include MG, Austin, Cooper, Jaguar and even the ubiquitous Cobras built by Shelby.  It is not uncommon to hear of them referred to as “Lucifer” because of their alleged history of causing vehicle fires.  One of the benefits of our Infinitybox system is that you can use practically any switch to control things in your car.  This includes a period correct Lucas switch in your restoration of a MG or a Cobra replica build.  Read below how to connect the Lucas 31788 headlight switch into the inputs on your Infinitybox MASTERCELL.

Our Infinitybox system has been used to wire some of the most advanced resto-mods and Pro-Touring builds.  At the same time, our customers use our system in a lot of classic restorations and component car builds.  The most popular component car that we see from our customers is the MK4 Roadster from Factory Five.  This is a great replica of the Cobra made famous by Carroll Shelby.  A lot of guys want to build this car and customize it to make it unique to them.  Other guys want to build it period correct to look like the original Cobras but with all modern systems under the skin.

We got a question this week from one of our customers building a Factory Five Cobra.  He wants to use the original headlight switch from Lucas in the car and wanted to know how to wire it to the MASTERCELL inputs.  He’s using the Lucas 31788 switch.  That’s an easy thing to do.

One of the advantages of our system is that it takes very little current to turn on a MASTERCELL input.  The actual amount is less than 1 milli-amp.  (0.001 Amperes).  This means that you don’t have to use high-current switches to turn your lights, fans, ignition or starter solenoid on or off.  The high-current part of the circuit is managed in the POWERCELL.  A lot of the alleged issues that Lucas had over the years came from too much current being pushed through their switches.  Our MASTERCELL completely eliminates that.

This diagram shows you the specifics on how to wire the MASTERCELL inputs for parking lights and head lights to the Lucas switch.

Picture of Infinitybox wiring diagram showing how to control headlights and parking lights from a Lucas Switch

Picture of Infinitybox wiring diagram showing how to control headlights and parking lights from a Lucas Switch

Terminal 4 on the switch needs to get connected to ground.  If you understand how the switch works, this may seem counter-intuitive, just trust us.  You can either connect this terminal directly to the chassis or use one of the black ground wires that is included in the MASTERCELL inputs harness.  Using one of the dedicated ground wires is our preferred way of wiring these kinds of switches.

From there, connect the MASTERCELL input for the parking lights to terminal 7 and the input for the head lights to terminal 8.  The switch is set up internally so that the parking lights will stay connected when the switch is in the headlight position.

Check the specific configuration sheet that came with your kit for the exact wire colors and connector locations for these inputs.  Different configurations may have different wire colors and connector locations.

You can read these blog posts to get more details about wiring the head lights and parking lights to the POWERCELL outputs.

That’s all you need to do to wire your headlights and parking lights to this Lucas switch.  When you turn on the parking lights or the headlights, the MASTERCELL will see the switch turn on and send the appropriate commands to the front & rear POWERCELLs to manage the lights.

You can download a PDF copy of this wiring diagram by clicking this link.  If you have any other specific technical questions, you can contact one of our technical support engineers by clicking this link.



In our last post, we hit the high-points of wiring the outputs on our Infinitybox POWERCELLs.  Over the next few posts, we are going to go into detail on wiring some of the specific loads in your car.  This post is going to talk about headlights.

Headlights are usually the easiest output to wire and we use them as an example when we’re helping guys wire their cars over the phone.  On the front POWERCELL, there is a dedicated output for the headlights.  Check your configuration sheet for the exact wire color.  This blog post will show you how to do this.  In the case of our 1967 Mustang project, the POWERCELL output wire for the headlights is the white wire.  This is output 5 on the B connector.

From the front POWERCELL, you are going to run the white output wire to your headlights.  It is usually easiest to run the wire to the closest headlight, then splice from there to go to the second headlight.  Essentially, you are wiring the two headlights in parallel.  You can use our Splice Saver Kit to make this connection easy and reliable.

In the previous post about wiring POWERCELL outputs, we talked about ways to connect wires together.  These options include butt-splicing, soldering and connectors.  You can built the splice between the two headlight bulbs in this splice.  This picture shows a simple schematic for wiring the two headlights off of a single POWERCELL output.

Picture of a simple schematic showing how to wire your headlights to the Infinitybox POWERCELL

Picture of a simple schematic showing how to wire your headlights to the Infinitybox POWERCELL

There are going to be two wires on each of your headlights.  One is the 12-volt power coming from the POWERCELL output.  The other is ground, which needs to be connected to the chassis.  If your high-beams are integrated into the same headlight housing, there may be multiple connections.  You need to consult the paperwork or instructions that came with your headlights.

If your headlights are incandescent bulbs, the orientation of the power input and ground wires do not matter.  The current will flow through the filament in the bulb in either direction.  If you headlights are HID or LED, the polarity will matter.  You need to consult the manual for the HID or LED headlight kit.

The standard headlight output on the front POWERCELL is designed for an incandescent bulb.  We can do things with a POWERCELL output that you can’t do with a relay.  Because we are using solid-state relays, we can do something called Pulse-Width Modulation.  That means that we can gradually ramp up the power to an output.

Incandescent bulbs have a high in-rush current.  When the bulbs are cool, the resistance of the filament is relatively low.  When you first turn on the bulb, it will draw a lot of current.  As the bulb and filament heat up, the resistance of the filament increases significantly, which limits the current to its steady-state draw.  This inrush current can be 4 to 10 times the steady state current.  You need to size you wire and the fuse to work with this inrush current.  We have done that for you in our choice of output harness wire.

We soft-start the standard headlight and high-beam outputs on the front POWERCELL.  This essentially smooths out the inrush, which causes less stress on the fuse, the wiring and the light bulb.  You get this feature automatically if you use the standard MASTERCELL input.

You can use this same soft-starting output for LED (Light Emitting Diode) headlight kits.  If you are using HID (High Intensity Discharge) headlights, you need to use a different input to the MASTERCELL.  There is a dedicated input to the MASTERCELL for HID headlights.  If you use this input, the headlight input turns on instantaneously without the soft starting.  We’ll talk more about MASTERCELL inputs in later posts.

While we’re at it, you are going to wire your high-beams exactly the same way as the headlights.  In the case of the configuration that we are using for this 1967 Mustang, the dark-blue wire from the front POWERCELL is for the high-beams.  This is output 7 on the A connector.  You are going to run the high-beam output from the POWERCELL to the first high-beam bulb then splice over to the second high-beam bulb.  Check the documentation that came with your bulbs for proper wiring.  The ground wire on the bulb should connect to the chassis of the car.

Keep watching our blog for more posts on wiring the different outputs on your Infinitybox wiring system.  Click this link to contact our team with questions.

Picture of simple leaded LED's

Wiring an LED

We got another great question from a customer today.  This one came in through our Facebook page.

“I’m going to be running LED headlamps and taillights on my Infinitybox-equipped car. Can you write-up a blog on the changes I’ll need to make in my wiring?”

Here are the changes that you need to make when wiring an LED light with the Infinitybox system:  absolutely nothing.

Our POWERCELLs turn things on and off including fans, ECU’s, pumps and lights.  Lights come in basically two flavors: incandescent and LED.  Incandescent lights were the original creation of Thomas Edison.  Up until a few years ago, they were used for all of the lights in cars including headlights, running lights, interior lights, brake lights and turn signals.

The trend in automotive lighting is towards LEDs or light emitting diodes.  This link will take you to a Wikipedia page talking about how they work.  LED’s have two main advantages of incandescent light bulbs.  First, they have no filaments or fragile parts so they last a long time.  Second, they are much more efficient than incandescent bulbs.  This means that they consume much less current to get the same level of brightness.

To go back to the question, you can connect an LED light in the place of an incandescent bulb and it will work correctly when connected to an Infinitybox POWERCELL.  The other question that we usually get related to LED’s is “do I need a load resistor when using LED turn signals?”.  The answer again is “no”.

Traditional turn signal flashers work by drawing current through a heating element within the flasher.  The flashers are expecting a certain amount of current being drawn by an incandescent bulb.  When you change to LEDs with a traditional turn signal flasher, you needed to add a load resistor that draws current through the circuit.  This compensates for the reduced current flowing through the LED.

With the Infinitybox system, you don’t need the load resistor to get your turn signals to work correctly.  We do the flashing of the turn signals and 4-ways through the processor on the POWERCELL.  The flashing does not depend on the amount of current flowing to the bulb.  To the POWERCELL, there is no difference between an incandescent bulb or an LED light.

To round out this question, there is one thing that you may need to do when wiring an LED into your Infinitybox system.  As we mentioned above, LEDs are much more efficient than their incandescent cousins.  It takes very little current to turn them on.  LEDs from different manufacturers are more or less efficient, depending on the materials that they may use.

Our POWERCELLs leak a very small amount of current out of the outputs.  We use this as part of our diagnostic system.  Depending on the efficiency of the LED, this diagnostic current may make the LED’s glow dimly when the light is off.  To eliminate this, you can simply connect a 10K (10,000 ohm) resistor between the POWERCELL output wire and ground.  An 1/8 Watt resistor or larger will be fine.  This picture shows you how to wire this in.

Picture of wiring diagram showing how to wire a bypass resistor with LED lights

Picture of wiring diagram showing how to wire a bypass resistor with LED lights

This bypass resistor shunts the diagnostic current through the resistor around the LED.  You can pick up a 10K resistor on-line.

You can download a PDF of this wiring diagram by clicking this link.

Please give our technical support team a call if you have questions about this post.

Automatic Headlights

We get a lot of questions about adding advanced features to our Infinitybox system. The reality of our system is that it is very easy to add modern functions to your car Here’s another great example.

A lot of customers want to add automatic headlights to their car. Some people call this a twilight function and practically every new car can do this. When it gets dark outside, the headlights turn on automatically.

To do this, you can use practically any light sensor. It just needs to make a connection when the light level gets dark. You are going to use this connection to ground the MASTERCELL input for the headlights. Remember that the MASTERCELL triggers an output on a POWERCELL when the input wire is grounded.

You can find simple photosensor relay modules on-line.  Amazon has a lot of options.  Try searching for “Photosensor Sensor Relay Module”.

The photoelectric switch simply needs power and ground. You should tap off of the ignition output on your POWERCELL to provide 12-volts to the switch. You can ground it locally in the car. The power and ground terminals are located on the side of the switch close to the white sensor connector. The power terminal is closest to the white connector and it is labeled VCC on the board. The ground terminal is on the side away from the white connector and it is labeled GND on the board.

On the other side of the board is a blue connector. The center terminal of this connector will connect to ground. You can connect this locally to ground or you can use one of the black ground wires in the MASTERCELL harness. There is a black jumper that may be located on a set of pins next to the relay on the board. See the picture below for more details. It is very important that this jumper be removed from the pins. You can do this with your fingernail or a small pair of needle-nose pliers. This jumper selects between ground switching the outputs on the relay or applying 12-volts from the relay. The MASTERCELL inputs are designed to be ground switched and they can be damaged if voltage is applied to them. You must make sure that you remove this jumper from the pins on the board.

Once you have the jumper removed, connect your MASTERCELL input to the left terminal next to the relay. See the diagram below for more details.

Lastly, take the white sensor cable and mount it in a place in the car where ambient light will hit it. You may have to experiment with the location of this sensor. There is also a potentiometer on the board that you can use to adjust the sensitivity of the sensor. Essentially, you need to adjust its location and the potentiometer so that the relay turns on when the ambient light falls below the threshold that you want.

You can have this light sensor as your only way to turn on your headlights. To do this, simply run the headlight input to the MASTERCELL directly to the light switch. You can also have it so that either the light sensor or the headlight switch will turn on your lights. To do this, wire the MASTERCELL input to both the headlight switch and the light sensor. You can split the MASTERCELL input into two runs, one for the headlight switch and one for the light sensor.

Image of a wiring diagram showing how to wire a simple photosensor relay to a MASTERCELL input

Image of a wiring diagram showing how to wire a simple photosensor relay to a MASTERCELL input

This diagram is just an example of one photosensor relay board that we found on Amazon.  Follow the instructions that came with the photosensor that you are going to use.

You can download a simple diagram from our website that shows you all of the details. This link will take you there.


Please give our technical support team a call if you have questions about wiring your twilight lights with this sensor.  You can click on this link to contact our team directly.