Cannot find an engine run signal.

Possible cause: Only a switched ignition signal is available instead of an engine run signal.. Install a voltage sensing relay (VSR) using the switched ignition signal. Connect a negative, switched ignition feed to the input of the VSR so that the output becomes your engine run signal. The relay requires +13.2V on the input to engage (rather than +12V like a traditional relay), meaning the switched ignition voltage will remain below 13.2V until the engine has been started and the alternator is charging the vehicle battery.

The reverse polarity indicator comes on when using a generator.

Possible cause: The way many generators have the output wired.. Press the 'TEST' button on the RCD and confirm it trips. If the RCD doesn't trip, you shouldn't use the 230V system and should consult a qualified electrician for advice.

The reverse polarity indicator comes on whilst outside the UK.

Possible cause: Many countries outside the UK do not earth the Neutral in the supply network.. Press the 'TEST' button on the RCD to confirm it operates and trips. If necessary, use a polarity reversing adaptor if you carry one with you when travelling outside the UK. If the RCD fails to trip, consult a qualified electrician.

The reverse polarity light comes on when on mains hook-up at a site in the UK.

In the first instance, contact the site warden to confirm the fault isn't with the site supply. Then have your hook-up lead inspected in case it is at fault (as a simple test you may be able to try a different lead). If you are unable to find a simple cause of the indicator coming on, you should have your 230V system checked by a qualified electrician.

Warnings displayed in the tow vehicle and some road lights may not function correctly when towing a Swift caravan fitted with LED road lights.

Possible cause: The tow vehicle's monitoring system expects a higher current draw (traditionally 1.75A from a 21W lamp) than the low current drawn by the caravan's LED road lights (around 0.25A from a 2W or 3W LED), causing the vehicle to fail to detect the load.. Integrate a VLM6 LED road light electronic control unit into the existing caravan wiring to add resistors that increase the load to a level within the towing vehicle's monitoring parameters. For 2019 model year caravans and 2018 model year caravans fitted with the larger format C44+ fuse box (introduced October 2017), the VLM6 unit is directly compatible. For 2016 and 2017 model year caravans, follow the specific VLM6 installation guidance with extra installation effort to fit the unit.

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Sargent • General Support

Sargent General Electrical System Support

Official technical documentation and workshop diagnostics for General Electrical System Support.

Master Troubleshooting & Diagnostics Matrix

Error Code / Indicator	Symptom / Meaning	Step-by-Step DIY Fix	Suggested Actions
`N/A`	Cannot find an engine run signal. Possible Cause: Only a switched ignition signal is available instead of an engine run signal.	Install a voltage sensing relay (VSR) using the switched ignition signal. Connect a negative, switched ignition feed to the input of the VSR so that the output becomes your engine run signal. The relay requires +13.2V on the input to engage (rather than +12V like a traditional relay), meaning the switched ignition voltage will remain below 13.2V until the engine has been started and the alternator is charging the vehicle battery.	DIY Safe
`N/A`	The reverse polarity indicator comes on when using a generator. Possible Cause: The way many generators have the output wired.	Press the 'TEST' button on the RCD and confirm it trips. If the RCD doesn't trip, you shouldn't use the 230V system and should consult a qualified electrician for advice.	DIY Check / Tech Fallback
`N/A`	The reverse polarity indicator comes on whilst outside the UK. Possible Cause: Many countries outside the UK do not earth the Neutral in the supply network.	Press the 'TEST' button on the RCD to confirm it operates and trips. If necessary, use a polarity reversing adaptor if you carry one with you when travelling outside the UK. If the RCD fails to trip, consult a qualified electrician.	DIY Check / Tech Fallback
`N/A`	The reverse polarity light comes on when on mains hook-up at a site in the UK.	In the first instance, contact the site warden to confirm the fault isn't with the site supply. Then have your hook-up lead inspected in case it is at fault (as a simple test you may be able to try a different lead). If you are unable to find a simple cause of the indicator coming on, you should have your 230V system checked by a qualified electrician.	DIY Check / Tech Fallback
`N/A`	Warnings displayed in the tow vehicle and some road lights may not function correctly when towing a Swift caravan fitted with LED road lights. Possible Cause: The tow vehicle's monitoring system expects a higher current draw (traditionally 1.75A from a 21W lamp) than the low current drawn by the caravan's LED road lights (around 0.25A from a 2W or 3W LED), causing the vehicle to fail to detect the load.	Integrate a VLM6 LED road light electronic control unit into the existing caravan wiring to add resistors that increase the load to a level within the towing vehicle's monitoring parameters. For 2019 model year caravans and 2018 model year caravans fitted with the larger format C44+ fuse box (introduced October 2017), the VLM6 unit is directly compatible. For 2016 and 2017 model year caravans, follow the specific VLM6 installation guidance with extra installation effort to fit the unit.	DIY Safe

Frequently Asked Questions

Q: What are the recommended system settings and leisure battery connection for vehicle storage?

First, ensure the leisure battery is fully charged using the built-in charger in the vehicle before placing it in storage. To charge the battery, connect the vehicle to the 230V mains supply, turn the charger on at the PSU (green push button) and leave to charge for 24 hours. If you have an active tracking subscription, it is important to keep a charged leisure battery connected at all times. For caravans, it is recommended to keep the leisure battery fitted and connected at all times, and to turn the power supply unit (PSU) off to save battery power. If you require temperature reading and remote control features, the PSU can be turned on, but you will need to monitor the leisure battery to determine if it needs charging (having a 40W or larger solar panel connected will help maintain the battery charge). For motorhomes parked outside with a solar panel fitted, keep the leisure battery connected, have the PSU turned on, and turn off the control panel over the door. For motorhomes parked undercover, in a carport, with a storage cover blocking the solar panel, or without a solar panel installed, turn the PSU off and leave the leisure battery fitted and connected to power the tracking unit over an extended period.

Q: What is split charging?

Split charging is the term used to describe charging of the vehicle battery and the leisure battery at the same time from a charging source. On motorhomes and caravans the charging source would be the vehicle alternator which is in turn powered by the engine.

Q: How do Sargent PSUs split charge?

Sargent power supply units (PSU) have a built-in split charge system. For this to work, the Sargent power supply unit (PSU) would need a connection to the vehicle battery, the leisure battery and also an engine run signal. When the engine run signal is detected, the internal split charge relay is energised and the two batteries are connected together so they both receive charge from the vehicle alternator. Charging would only occur if the power supply unit (PSU) detected an engine run signal. If no engine run signal is detected this would mean no charging source is present and these connections would be electrically separated, ensuring that one battery does not draw current from the other.

Q: Why do the batteries need to be separated when they're not being split charged?

It is important to ensure that the vehicle battery is isolated from the leisure battery so you don’t flatten the vehicle battery and the engine can always be started, but you also don't want the leisure battery to be drawn upon when starting the engine because leisure batteries are not designed for high current output over short periods of time and they can be damaged.

Q: Engine run signal or switched ignition, what's the difference?

An engine run signal would give you +12V when the engine is running and 0V when the engine is off. A switched ignition signal would give you +12V with the ignition on and the engine is not running and 0V when the ignition was off. It is important to find an engine run signal and NOT a switched ignition because if you find a switched ignition signal the split charge relay will engage and both batteries will be connected together during engine cranking which can damage the leisure battery.

Q: What if I can't find an engine run signal?

If you can’t find an engine run signal you can use a switched ignition signal but you would also need to use a voltage sensing relay (VSR).

Q: What is the difference between an engine run signal and a switched ignition signal?

An engine run signal provides +12V when the engine is running and 0V when the engine is off. A switched ignition signal provides +12V with the ignition on and the engine not running, and 0V when the ignition is off. It is critical to find an engine run signal rather than a switched ignition signal when split charging, because a switched ignition would cause the split charge relay to engage and connect both batteries together during engine cranking, which can damage the leisure battery.

Q: What should I do if the reverse polarity indicator briefly flashes when my charger turns on or off?

When the charger is turned on or off the indicator may give a brief flash or short series of rapid flashes. This is just down to the components in the charger charging and discharging as power is connected or disconnected. This is quite normal and nothing to worry about, and requires no action.

Q: Why does the reverse polarity indicator come on when I turn my charger on?

In the majority of our systems, the reverse polarity indicator is only switched into circuit when the charger is turned on. This is done because it would interfere with readings taken when your electrical system is given its regular inspection. As the charger must also be turned off when tests are performed, the charger switch provides a safe and convenient way to disconnect them both for testing.

Q: Is my caravan 230V system safe to use outside the UK where they don't earth the neutral?

Yes. In many countries outside the UK, such as most of Europe, they don't earth the Neutral in the supply network as we do in the UK, meaning they are not polarity conscious with both conductors considered 'Live'. They use MCBs which break both conductors. All of our systems are fitted with MCBs which break both Live and Neutral to keep the vehicle user safe in the event of a fault, and standard equipment fitted in the van will be suitable for use on the continent. However, if you are unsure if an item of equipment you plan to use in your van whilst abroad is safe, you should contact the supplier or manufacturer for advice.

Q: My electrics turn off when I start the engine...Can I disable this?

This is quite normal and to be expected. For safety reasons and to meet EMC (Electro Magnetic Compatibility) directive 89/336/EEC, all Sargent systems shut down the habitation 12V system when you start the engine. In caravans it is a complete shutdown as no one should be in the caravan whilst it is in motion. In motorhomes, there may be a 12V socket and/or USB socket adjacent to a travelling seat (i.e., one fitted with a seatbelt). No attempt should be made to disable the engine running feature in any Sargent system. It is dangerous to do so, and will also affect operation of the van such as fridge functions and split charging.

Q: Do I need to install a DC-DC charger?

Yes, a DC-DC charger is beneficial or necessary when dealing with smart alternators, regenerative braking, or lithium batteries. Smart alternators reduce voltage when the vehicle battery is nearly full, which can leave leisure batteries undercharged if using a traditional split charge relay. Regenerative braking systems can boost alternator voltage output as high as 15V+, which can overcharge some leisure batteries (such as Gel). Furthermore, lithium batteries feature a built-in BMS that accepts high charging currents (up to 70A), which can cause fuses to blow on circuits designed for traditional lead-acid batteries. A DC-DC charger helps by providing a fuller, more rapid charge while driving, compensating for cable and connector losses, delivering multi-stage charging tailored to specific battery types (AGM, Gel, Lithium, etc.), and limiting maximum current to prevent overcharging and blown fuses.

Q: What to do in the event of a theft

In an emergency theft situation please contact the tracking monitoring station on 0345 6027302. The station operates 24 hours a day, 7 days a week. Before contacting them please ensure you know your caravan or motorhome serial number. For caravans this is the last 10 digits of the CRIS number (e.g. SWH0123456). For motorhomes this is the unique build number starting MH, ME or AP number (e.g. MH01234).

Q: Why do vehicle warnings happen when towing a caravan with LED road lights?

Vehicle manufacturers are required to monitor directional indicators and display a warning if they fail. Traditionally, road lights used a 21W lamp drawing 1.75A. Modern LEDs often draw only 2W or 3W (around 0.25A). If a vehicle's monitoring parameters are set to look for a higher load (e.g., down to 1A), it will not detect the 0.25A load from the LED and will falsely display a failure warning. Different vehicle manufacturers use different monitoring parameters, which is why some vehicles display warnings while others do not.

Q: What is the difference between the VLM4 and VLM6 units?

The VLM4 unit was an older electronic control unit produced in 7 different versions depending on the vehicle manufacturer, but these are now obsolete and no longer manufactured. They have been replaced by the VLM6 unit, which is a single 'one size fits all' universal version designed to be compatible with most towing vehicles.