Master Switch & Pull Cable

Location	The master switch is fitted onto the dash blanking plate within the centre console. The blanking plate is located within the centre console effectively housed by the upper dash facia. The pull cable is attached to the dashboard and routed through the firewall and onto the scuttle tray/panel found under the passenger side of the windscreen.
2024 Regulations Reference	– 5.6.1.2 – 5.10.4
Original Parts to Discard	– Radio
Parts to Add	– Master Switch – Pull Cable – Cable Bracket/Mount – Fasteners – Cable Ties – Warning Stickers
Important Checks	When operated, the master switch must isolate all electrical systems with the exception of any that may operate the fire extinguisher system (not applicable in our case with mechanically operated extinguishers. The pull cable must be routed and secured in a fashion that allows free operation of the master switch.

Requirements

In this lesson, we take a look at the master switch which we fit within the centre console and the associated power cables and emergency pull cable which are routed through the bulkhead/firewall and within the upper dash facia. This part of the dash area was removed, modified and refitted so that we could fit the dash blanking plate to which we now install the master switch.

A battery cut-off master switch must be installed on all competition vehicles. When operated, this switch must isolate all electrical systems with the exception of any that may operate the fire extinguisher system. The pull cable/operating button must be situated within the scuttle panel situated at the lower edge of the front windscreen.

Remember, excluding the dashboard, centre console, dash top speaker covers and steering column cowlings must all remain intact and correctly fitted, all other interior trim and fittings may be removed. You’ll notice in some of our images we feature our flocked dash a styling finish which you of course can choose to introduce to your dash areas.

The original dash binnacle and instrument cluster must remain fitted in the original position. On re-assembly, it is permitted to remove the circular air vents and neatly trim the ends of the dashboard to allow fitment of the roll cage.

Important Master Switch Information – If you disconnect the battery while the engine is running, an alternator could be damaged by a voltage spike. This damage can be avoided by the installation of the master switch which gives the alternator output a safe path to ground immediately after the switch is turned off. FIA approved master switches have an auxiliary set of contacts (labelled “W”) which are open when the switch is on, but which make contact when the switch is turned off.

An alternator that is operating can still put out electricity, so simply disconnecting the battery will not always stop an engine. The master switch has a third set of contacts (labelled “Z”), which also interrupts the ignition circuit when the switch is turned off.

Master Switch Contacts

1. Mains (Normally Open, switch off means circuit is off): These 3/8″ stud/threaded terminals break contacts in order to isolate the battery when the switch is turned off.
2. W (Normally Closed, switch off means circuit is on): These 1/4″ spade/threaded terminals connect only when the switch is turned off, to provide the alternator output with a safe, loaded path to ground.
3. Z (Normally Open, switch off means circuit is off): These 1/4″ male spade terminals break contact to interrupt power from your ignition switch to the ignition system when the master switch is turned off.

Note that all three sets of contacts are isolated from each other for extra fail safe. The power going through the main terminals is not distributed to the ignition system.

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Suggested Assembly and Modifications Method (7 Steps)

Safety Tip – When fitting the master switch and wiring please ensure that the battery is not connected to the electrical system. It is your responsibility to ensure you fit the master switch correctly and to follow the rules and regulations set by the BRSCC, safety advice and regulations by MSUK.

Step 1. Dash Blanking Plate Modification (To accommodate the switch)

In order to allow the dash blanking plate to accommodate the master switch, you must remove the centre console again. In the centre console/dash blanking plate lesson, you will remember we advised you to simply push the console back into position in readiness for this procedure.

Once you have removed the centre console, unplug any wires you reconnected so that the console is free from the car.

Step 2. Centre Console Drilling

The centre console must now be drilled to accommodate the 2 switch fasteners. Place the centre console on a suitable surface to protect it when drilling. Hold the switch in the desired orientation as illustrated below (key to the top right when tuned to the closed-circuit position) and mark the drilling holes with a suitable marker. Next, hold the console in place and drill 2 securing/fixing holes using the switch as a template. (Notice the orientation of the switch in the images below)

Safety Tip – When drilling please wear the required PPE such as gloves, face mask, goggles and ear defenders. Ensure the blanking plate is secured with a suitable clamp to avoid risk of injury.

Tool Tip – When drilling the holes drill them from the front to the back of the blanking place to avoid damaging the front face of the plate. Then ensure you dot punch the drilling area first and de-burr the holes made to avoid risk of injury.

Step 3. Attach the Master Switch

Once you have drilled the two securing/fixing holes feed the switch into the pre-made hole in the blanking plate (with the red key removed) and add 2 suitable fasteners to the switch to secure it in place. In this case, we opted for cap head bolts, washers and nylon locking nuts for security.

Tool Tip – Take care not to overtighten the fixtures to avoid damaging the plate, particularly if you have coated or painted it.

Step 4. Routing and Wiring

Once you have attached the master switch to the blanking plate it is time to connect the two main feed wires that serve to cut power to the engine and thus the electrical system. The two power feeds (which you are required to make) are fed into the car from the engine bay, through the bulkhead/firewall and up through along the upper dash (see routing and wiring guidance below). In the diagrams below we have already fitted the power leads to the electrical system.

Routing: The main stud terminal power cables need to be routed from the engine bay area, into the cabin. You can carry this out as you wish (by means of your own additional wring) but it is your responsibility to ensure that the master switch is fitted correctly and safely and wired as per the guidance provided in the MSUK Yearbook section 5.30.1-4 ‘Driver Master Switch’ and conform to the regulations set by the BRSCC, in this case, section 5.10.4 ‘Electrical’ as per the 2024 regulations.

In our example below we chose to route the power cables from the cabin through to the engine bay (passenger side) via a ‘grommet’, in this case, we 3D printed a ‘cable holder’ which is bolted to the bulkhead/firewall and harnesses the 5 cables/pipes that need to be routed into the engine bay. This reduces the risk of entanglement and chaffing on the metalwork.

In order to fit this item, we drilled out the bulkhead/firewall with a suitable step drill and drill bit for the fasteners and fitted it accordingly and fed the electrical wiring and pull cable through the bulkhead/firewall into the cabin on the passenger side.

The cable is then routed under the passenger side dash and up through the upper dash facia and into the centre console space.

Step 5. Attach the Wiring

Once you have attached the master switch to the blanking plate it is time to wire in the rest of the connections that serve to cut power to the engine and thus the electrical system.

1. Turn the car off and disconnect the negative battery cable if the battery is still installed. One 10mm female ring terminal on the master switch is connected to the battery positive terminal via a suitably rated cable.
2. Install one 10mm female ring terminal on the master switch connected to the starter motor with a ‘jumper feed wire to male terminal ‘1’ via a female spade terminal suitably rated cable.
3. The main power jumper feed is connected via a female spade terminal to the male spade terminal ‘W’ and through the supplied resistor to ground from the other side of the male spade terminal number ‘1’.
4. The ignition switch is connected to the master switch via male spade terminal number ‘2’ and the ignition coil via male spade terminal ‘Z’ with suitably rated wires.

Once this has been completed and you have checked your connections only now can you reconnect the negative battery cable.

Test your master switch installation by turning the switch to the on position and starting the car. The battery should power the vehicle and charge as normal. Whilst the engine is running, turn the switch into the off position. This action should turn the engine and all circuits off.

Step 6. Attach Emergency Pull Cable

Tool Tip: Follow the guidance in the ‘Scuttle Tray/Panel’ lesson for additional information on modifications to accommodate the emergency pull cables’

Once you have attached the power cables (and have checked the master switch operation) and have re-fitted the centre console, the final task is to connect the emergency pull cable that race marshals operate from the outside of the vehicle. The master switch emergency pull cable is fed through the scuttle tray/panel under the passenger side of the windscreen.

The panel trim will need to be drilled to accommodate the wire and handle mechanism, however, we found that the upper trim panel cover is not ideal and in some cases strong enough to hold the cable when operating the handle and the trim often becomes unsettled or detached from the screen (shown in image 1-2 below).

The best solution we found was to manufacture your own mounting/stay/bracket that attaches to the scuttle tray from which to attach the emergency pull cables to as per diagrams 3 onwards below: (In some of the images you’ll notice we are also fitting the fire extinguisher pull cable. You are permitted to fit each cable in any order left to right)

Step 7. Attach Inner Cable to Switch

Once you have fitted the handle mechanism to the scuttle panel and rooted the cable into the car it is time to connect the outer cable to the dashboard and the inner cable to the master switch itself.

The outer cable can be attached to the dashboard as you see fit, but we recommend following similar steps to the following:

1. Cable security – We recommend using P-Clips or a suitable fastener that do not ‘pinch’ the wire to ensure free inner cable movement on the location shown below. They can be attached with short self-tapping screws or rivets for example.
2. Cable Routing – You must not overly tighten the outer cable, avoid tight ‘S-bends’ to reduce inner cable snagging and the risk of system failures.
3. Inner Cable – Once you have routed the cable, install a suitable bracket in which to secure the outer cable, this way the inner cable can operate independently. The outer cable needs to be held securely so that the inner cable can be operated by the master switch or pull handle from outside the vehicle. We opted to use a small 90 degree bent bracket with a bike cable adjuster incorporated for adjusting cable slack and attached it to the blanking plate.
4. Final Fitment – Feed the outer cable into the adjuster, and the inner cable into the master switch (on position). Add the cable fastener and adjust slack to around 2mm so there is no tension and risk of the master switch turning to the off position. Trim or tidy away the remaining excess inner cable to suit.

Driver – Test your master switch ‘manual operation’ (switching mechanism) by turning the switch by hand from the on to off position (can you reach, is the cable free etc)

Marshal (a person outside the car) – Test your master switch ’emergency pull cable operation’ (switching mechanism) by pulling on the handle (it must turn the master switch from the on to the off position in an easy, free, non-snagging fashion).