# towbar electrics



## 125182 (Jun 29, 2009)

looking for help, not had motorhome long and i am trying to wire up a tow car (chevvie matiz), wired up the sockets and lights plugged it into van and ... nowt, indicators just about glow but thats it... tested voltage and get 9v on all pins on van socket and on 3.4v on matiz rear lights. all lights work on van and tow cable joints look ok so i'm stumped.. dont know what else to look at .


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## DABurleigh (May 9, 2005)

Trace back to where you get 12V, 'cos you are losing volts. What did you do for the relay?

Dave


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## 125182 (Jun 29, 2009)

what do i need a relay for?


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## DABurleigh (May 9, 2005)

Are you confident your existing lighting circuits can handle the extra load you have placed on them? If so you don't need a relay. Do your existing lights work fine, and just your extensions are dim or not working (all at the same time I'm talking about here)?

Do you know how to use a multimeter to diagnose basic electrical faults?

Dave


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## CliveMott (Mar 10, 2008)

Killer question then Dave!


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## poleman (Aug 31, 2008)

*towbar*

I have wired quite a few towbars in my time but you will need to give us more info.
Was the van towbar already wired or have you done it?
How have you wired the car, is it a light board or through the car lights?

If the towbar was already wired it should have a heavy duty relay for the indicators and by law needs an audible or visual warning of indicator failure. :wink:


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## ytank (Jan 9, 2008)

if its a new ish van you will have fail safe light fitted volts are low like most of the posts are saying. you will need a relay and there are about 26.pound and you will need a good 12v power supply at the rear of the van fuse it at 20 amp you will be ok at that good luck


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## pete4x4 (Dec 20, 2006)

What year is your motorhome, is it a factory fitted towbar?


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## 125182 (Jun 29, 2009)

van is a 52 plate swift on a ducato, the tow bar was already fitted and all the lights work fine there is also a audio alarm fitted on the indicators . the tow socket is wired in at the point where the original rear lights would have been and all the lights on the back end of van work but when i plug in the A frame the car inidcators flash but are dimmer than should be and stop/tail just a glow. the wires are scotchlocked into the cars wires next to each light. when i plug in the A frame the van lights / indicators stay on full power no disco lights. not 100% with multi meter but when test voltage on tow socket it says 9v when engine off and 10.4v when running when i put it on battery it says 14v with engine running. after spending all day yesterday checking sockets, cleaning bulb holders , wiring and re checking all wiring on the car ( if i operate all the light functions on the car there is 12v at the tow socket connector under the bonnet for A frame to plug into)i am getting hacked off with it, only thing i haven't checked is where the tow socket is wired into the van loom


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## DABurleigh (May 9, 2005)

Personally I find that very difficult to follow but suggest with Matiz connected and hazard flashers going you wiggle/squeeze the scotchlock connectors.

Dave


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## pete4x4 (Dec 20, 2006)

Now I'm not sure on this but I don't think you can just scotchlok your A frame to the cars lights. As an engineer I thought you had to do it via relays so that you isolated the lamps from the cars systems. I didn't think you could run them in parallel.
I'm trying to think of the consequences of not doing it with relays, the first would if you left the lights on in the car the motorhome would then charge the car's battery via the sidelights is one that springs to mind.
The hazard relay could probably cause some interesting effects?

All this is negated though if you make sure everything is off on the toad

I'm not sure, I would use relays but then I might be over engineering it.

The main question is why are you getting only 9.4 volts at the socket with nothing connected. If you are measuring that against the earth on the socket then I would suggest that earth is dodgy, Does it still read 9.4 volts using a chassis earth on the motorhome?


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## camoyboy (May 9, 2005)

Hi,
when you are checking the socket on the MH, are you using the earth pin in the socket for the return? If so try earthing direct to chassis (not towbar, see later) as it could be a poor earth connection to the socket.
I had this problem where the earth wire was connected to the towbar, which was plastic coated!! I re-connected direct to metal chassis and all was well.
Colin


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## poleman (Aug 31, 2008)

wiring is a pain at best but very rewarding when you find the fault and fix it.

Firstly you need 12volts at each output terminal of your vans towing socket (not earth). check each one with the earth pin on the socket, if it is less than 12v check them again with an earth point on the van chassis if it is now 12v your socket earth is faulty. Scotch locks are not ideal for outside use they corrode, this could cause your problem.

Secondly if your car lights are scotchlocked then you will be powering all the bulbs in each circuit ie front and back 3 indicator bulbs and two side light plus number plate and probably panel lamps.

you are doing this on only 9v through a socket, plug, cable and vehicle loom you have many points for problems if every thing is in good order.

Good luck, chin up keep smiling you will sort it one way or another.


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## rupert1 (Feb 13, 2009)

starsatnight said:


> looking for help, not had motorhome long and i am trying to wire up a tow car (chevvie matiz), wired up the sockets and lights plugged it into van and ... nowt, indicators just about glow but thats it... tested voltage and get 9v on all pins on van socket and on 3.4v on matiz rear lights. all lights work on van and tow cable joints look ok so i'm stumped.. dont know what else to look at .


Modern car systems are complicated with multipexed and can-bus in common use but even if your van does not have these it will use a simple bulb failure monitoring system, and you need to wire towbar using a three way bypass. Whatever type you have a smart bypass relay will work, plenty on Ebay for sale. If you do not use the bypass relay the towbar system will not work once you plug extra lights into it either from a car or trailer board.


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## ytank (Jan 9, 2008)

a bit of a mess on but i would just get a tail board much easier i do this on the back of my fiesta


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## 125182 (Jun 29, 2009)

thanks all for your help, cleaned all the connectors on van towbar and where it wires in got voltage up to 11v , same voltage on socket earth and wire straight from battery and chassis. think the main prob lies within the matiz as tail lamps are still on the dim side but brake and indicators are fine, even managed to hook the car into another motorhome and its still the same and he tows a fiat cinq with no light probs , so will turn attention on matiz , once again thanks all for your input.. lighting board looking fav for now..


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