Universal Electrics
Universal electrical kits are the traditional way that towbars have been wired for years. They allow for connection to the vehicle lighting by use of snap connectors.
How Universal Electrics Work
Using a tester, you find the correct wire on the vehicle (for example the left-hand side light) and then connect the black wire from the 12N socket to this using a snap connector. You would continue this with all the connections.
Universal electrics can be used for single, twin and 13 pin electrical connections. With universal electrics, the fitting of certain monitors or relays is required depending on what electrics you are fitting and the vehicle.
Audible Monitor
UK law requires that notice is given on the status of the trailer indicators. With universal electrics, an audible monitor (often called a buzzer) is connected in series with the indicator connections.
When the trailer is connected and the indicators are on, it makes a buzzing noise to confirm that the indicator is working correctly.
By-Pass Interface Relay
Since around the year 2000, vehicle manufacturers have been making vehicle lighting systems more complicated, requiring the use of by-pass relays when fitting universal electrical kits. It started with vehicles such as BMW, Mercedes and Audi and is now present in over 60% of new vehicles.
Vehicles may have different reasons for requiring a by-pass relay. Many vehicles that we recommend be fitted with a by-pass relay will work without it. However, if you get a fault on the trailer, a high current in the trailer lighting system could cause very expensive faults to your vehicle.
It is becoming more common for a by-pass relay to be required on vehicles. Even some vehicles will not work with a universal electrical kit unless a by-pass relay is fitted.
7 Way By-Pass Relays
Most vehicles require the fitting of a 7 Way By-Pass relay. These relays include an Audible Monitor inside, so no separate audible monitor is required.
Split Charge Relay
A self-switching combination relay is only used when fitting 12S electrics. The relay monitors the voltage in the vehicle and only provides power to the switched connections when there is sufficient voltage in the vehicle.
This is usually about 30 seconds after the vehicle has been started (and for about 30 seconds after the vehicle has been switched off). This means that when towing with your caravan, if you pull into the services for a meal, you don't have to worry about the caravan leisure battery being fully charged and your vehicle battery being dead.
Five connections are made to the relay:
- •Direct power feed (usually) from the battery
- •Earth
- •Switching Connection 1 (to 12S socket Pin 2) which charges the caravan leisure battery
- •Switching Connection 2 (to 12S socket Pin 6) which supplies the caravan fridge
- •Permanent Live Connection (to 12S socket Pin 4) for the caravan power supply