Towbar Fitting - Electrics

[RPWC]

I just drilled a hole at the top of the spare wheel well,that way you don't get water ingress and it's handy for the wiring harness.

[COLVERT]

I ran the power supply directly off the battery, through an inline fuse and then underneath the car to the rear. In through the wheel well.
No work inside the car; no trim removal. Took all of half an hour.--

[IverRover]

Posted this question earlier on the technical help section and maybe someone here can help please.

Already fitted a towbar and 12N electrics but we have now gone and bought a caravan so I need to wire up 12S socket.

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Connected the wires between split charge relay shown in photo and towbar socket, and now need to connect power feeds.

Please correct me if I'm wrong (probably), but looking at running a wire with a 20amp in line fuse for the constant 12v feed, from a thick brown and black tracer wire on rear of passenger fusebox.

As per the instructions in the other photo at point 4, wire to Ign terminal on relay, I am stuck where to take the feed from. ' 12v when ignition on but NOT when starter motor is being operated, such as supply to wipers'.

Pointers please

[HarryM1BYT]

Originally Posted by IverRover

As per the instructions in the other photo at point 4, wire to Ign terminal on relay, I am stuck where to take the feed from. ' 12v when ignition on but NOT when starter motor is being operated, such as supply to wipers'.

Pointers please

Most installers these days use a voltage sensing relay, mounted in the boot area, rather than the warning light switched type that you have. The reason being that the later type involve more work to install and can be tricky on a modern car to actually use.

The feed you mention behind your glove box, is probably not even connected to the engine fuse box, it will be tucked up out of the way under the fuse box and will need a crimped terminal fitted and plugging in to the underside.

Can I suggest that for best results you do things this way?

Connect the above feed to the fuse box via a 30amp fuse, in the box - the correct fuse way for a trailer supply is marked.

Run at the minimum a 4mm or better a 6mm main feed from behind the glove box into the rear of the boot, close to your tow bar. That will then be an unswitched permanently live feed.

Add a voltage controlled relay on the end of it, with two outputs, one to the fridge circuit, the other to the caravan battery charging circuit. Insert a fuse of 20amps into each of those two circuits, so if there is a fault on one circuit it doesn't blow both circuits.

The larger than normal feed, makes for both your fridge and battery to receive higher voltage, less volts drop along the relatively long cable run. Both will work much more efficiently, with less voltage drop.

The voltage sensing relays sense the voltage rise, when the engine is started and fall when the engine is stopped. It may need some fine adjustment via a tiny screw, to operate correctly once fitted.

[IverRover]

Originally Posted by HarryM1BYT

Most installers these days use a voltage sensing relay, mounted in the boot area, rather than the warning light switched type that you have. The reason being that the later type involve more work to install and can be tricky on a modern car to actually use.

The feed you mention behind your glove box, is probably not even connected to the engine fuse box, it will be tucked up out of the way under the fuse box and will need a crimped terminal fitted and plugging in to the underside.

Can I suggest that for best results you do things this way?

Connect the above feed to the fuse box via a 30amp fuse, in the box - the correct fuse way for a trailer supply is marked.

Run at the minimum a 4mm or better a 6mm main feed from behind the glove box into the rear of the boot, close to your tow bar. That will then be an unswitched permanently live feed.

Add a voltage controlled relay on the end of it, with two outputs, one to the fridge circuit, the other to the caravan battery charging circuit. Insert a fuse of 20amps into each of those two circuits, so if there is a fault on one circuit it doesn't blow both circuits.

The larger than normal feed, makes for both your fridge and battery to receive higher voltage, less volts drop along the relatively long cable run. Both will work much more efficiently, with less voltage drop.

The voltage sensing relays sense the voltage rise, when the engine is started and fall when the engine is stopped. It may need some fine adjustment via a tiny screw, to operate correctly once fitted.

Thanks for that. Off to get the relay and wire you suggest now.

[HarryM1BYT]

Originally Posted by IverRover

Thanks for that. Off to get the relay and wire you suggest now.

I have been asked for more details on the voltage sensing relay. The one I suggested is called the Smartcom. It should be a stock item in most good car accessory shops, certainly in caravan parts suppliers stock.

It has a small adjustment on the unit to set the trigger voltage. It may need some adjustment once fitted, so that it only makes when the engine is running and the voltage rises. This type of relay is very sensitive to voltage drop between the fuse box and the relay at the back. There have been cases where a less experienced fitter, who doesn't appreciate that cables need to be sized for both current and voltage drop, have installed cable sized for the current alone.

You then get a situation where the voltage rises, the relay closes, which then puts the cable under load. The voltage then drops and the relay does what it should and opens again - rinse and repeat, until you arrive at your destination, with an under charged battery and a fridge which has defrosted.