General towbar electrics
- Thread starter ferox9311
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General towbar electrics
I am assuming that the Doblo DOES NOT HAVE smart CAN Bus based lighting units.
For simple trailer wiring you need a 7 way bypass relay unit and a separate fuse 15A feed directly from the battery +ve terminal.
The +ve feed wire should be a MINIMUM of 2.5mm.sq. CSA as should the earth return. Earth return goes the a suitable chassis eathing point at the rear of the car. Do not run the return back to the -ve terminal of the battery.
If wiring for dual 7 pin sockets (trailer + services) or combined 13 pin (trailer + services) then you need TWO fused feed wires of 2.5mm.sq . You will also need voltage sensing relay to switch the services power feed. This stops your caravan fridge etc. from draining the car battery when the engine is not running.
If you don't have a Doblo wiring diagram then you will have to manually trace each of the wires from the back of the light units to identify which wire supplies which bulb. An easier and more reliable was is to buy a multimeter which has a current clamp measuring probe. Now you just get somebody to operate the lights as you work your way round clamping each wire looking for current readings in sync. with each light operation.
Lastly, when making connections between the 7 way relay wires and the car wiring do this as far away as possible from the light units. At least 12 inches away. A good place is around the inner wheelarch area. Here you unwrap the insulating tape for about 6 to 12 inches to expose the individual insulated wires. You will be able to easily fan-out/separate them and thus make connecting easier. Don't tape them back up again until you habve tested that everything is wired ok and works.
The other reason for connecting well away from the light units is that if you screw up, or later have bad connections then it is very easy to cut out sections and rewire. YOU DO NOT want to mess around at the light units as problems here will be difficult to rectify and could possibly lead to damaged light unit connetors which are very difficult to replace.
For simple trailer wiring you need a 7 way bypass relay unit and a separate fuse 15A feed directly from the battery +ve terminal.
The +ve feed wire should be a MINIMUM of 2.5mm.sq. CSA as should the earth return. Earth return goes the a suitable chassis eathing point at the rear of the car. Do not run the return back to the -ve terminal of the battery.
If wiring for dual 7 pin sockets (trailer + services) or combined 13 pin (trailer + services) then you need TWO fused feed wires of 2.5mm.sq . You will also need voltage sensing relay to switch the services power feed. This stops your caravan fridge etc. from draining the car battery when the engine is not running.
If you don't have a Doblo wiring diagram then you will have to manually trace each of the wires from the back of the light units to identify which wire supplies which bulb. An easier and more reliable was is to buy a multimeter which has a current clamp measuring probe. Now you just get somebody to operate the lights as you work your way round clamping each wire looking for current readings in sync. with each light operation.
Lastly, when making connections between the 7 way relay wires and the car wiring do this as far away as possible from the light units. At least 12 inches away. A good place is around the inner wheelarch area. Here you unwrap the insulating tape for about 6 to 12 inches to expose the individual insulated wires. You will be able to easily fan-out/separate them and thus make connecting easier. Don't tape them back up again until you habve tested that everything is wired ok and works.
The other reason for connecting well away from the light units is that if you screw up, or later have bad connections then it is very easy to cut out sections and rewire. YOU DO NOT want to mess around at the light units as problems here will be difficult to rectify and could possibly lead to damaged light unit connetors which are very difficult to replace.
Last edited:
https://www.fiatforum.com/doblo/116217-towbars-here-we-go-again-2.html
Post 16 gives all the colours.
I was told by owners and some manufacturers that I didn't need to buy the relay (but I fitted one anyway)
Post 16 gives all the colours.
I was told by owners and some manufacturers that I didn't need to buy the relay (but I fitted one anyway)
If your car has traditional based wiring (i.e. battery -> switch -> bulb -> earth) then a bypass relay is not required. If you have bulb failure detection circuits (most more moder fiat models do) then a relay should be fitted. There are two other advantages of fitting a 7 way bypass relay unit.
1) Legal requirement of audio warning for trailer indicator light failure is already included
2) Protects the car wiring and switches from the additional lighting loads and accidental overload.
1) Legal requirement of audio warning for trailer indicator light failure is already included
2) Protects the car wiring and switches from the additional lighting loads and accidental overload.
, now i can wire in my towbar
