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Electronic Control Units (ECU) and Towing Looms

by | May 17, 2018 | Trailer & Caravan Safety | 0 comments

Why do I need an Electronic Control Unit (ECU) on my towbar?

It would be true to say, being an Electrician, I can wire almost anything from high voltage to 12 volts in a car or caravan.

Then along came the computer in motor vehicles. Computers are energy management systems. Computers monitor and control most of the energy associated with a motor vehicle including the 12v system.

Your cars electrical system has been designed to examine all circuitry every millisecond and raise alarms when the car’s computer identifies any system out of specification.

These alarms include low volts, high volts, cable temperature, etc as it examines even the humble light bulb.

When an installer adds cable to a plug at the tow bar then he is adding resistance called OHMS. The car computer only recognises factory-installed settings, therefore, it issues a fault and renders that circuit inoperable.

There are two fixes available

  • You can install an ECU (image to the right). This controller also has an image above.
  • Or a more expensive but convenient option is to purchase a plug and play look kit.

This simple ECU has 5 pole or circuits and the main power circuit. It draws power from the battery and powers lights through relays in the ECU.

Therefore the car computer does not know it is connected as there is no extra circuitry or resistance that can be detected by the vehicle computer.

The plug and play loom kits more expensive simpler to install. A photo of a simple plug and play loom is below.


Do yourself a favour and install a cable larger than required from your battery.

If by chance you need more power around the tow bar area then you need not upgrade your power feeds.

Please remember to size your earth return the same size or larger than your main power cable.

There is a good article on Dee Shackle for tow bars here.


© Steve Wotherspoon 17th May 2018


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