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Solderjoint

Side lights car fuse blowing

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Hi,

 

I have an issue with my 2 x 10amp car side lights fuses blowing when my fleetwood colchester 2002 is connected.

The fuses don't blow in the car if I don't attach the caravan onto the tow bar.

Neither do the fuses blow if the engine is running or just ignition on to run the lights.

They only blow when the caravan is hitched to tbe tow bar and the side lights are turned on! They blow in a max of 5 secs

I have replaced the 12n plug and all bulbs on the caravan. I have cleaned all joints with emery cloth. 

NOTE: I do not connect my grey 12s lead.

Any advice would be welcome, thanks in advance

 

Chris

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Only blows when connect to towball sounds like a issue in the plug with the wiring and possibly a earth wire issue connected wrong or a loose strand of wire touching another contract . 

 

 

 

Dave

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8 hours ago, CommanderDave said:

Only blows when connect to towball sounds like a issue in the plug with the wiring and possibly a earth wire issue connected wrong or a loose strand of wire touching another contract . 

 

 

 

Dave

Hi,

 

I have changed the 12N plug. Do you 5hink its a bad earth then?

 

Chris

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Sounds like a short between the feed to the lights and earth within the caravan plug. Quite likely a single whisker of copper bridging the pins.

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Is this a new issue with an existing outfit, or is it a new car or caravan?

I'm assuming this fault happened before the plug change and you have wired it as per the colour code.

If it's an existing caravan, I would remove the rear light and marker bulbs and then check with a multimeter the continuity to earth - check both the wire earth and the van chassis. It should, of course be infinity.

Check for a good connection (only a couple of ohms, preferably zero) between the earth return wire on the plug and the van chassis. It may be that the earth wire has broken, or almost broken (melted??) and you have a short circuit somewhere that is apparent when hitched up as the van gets a better earth connection. Check for water ingress to you light units. Do you have a high level marker light on the side? I've always considered these to be poorly made in my experience.

 

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This is a little more complex than it might at first seem.

 

Sidelights are fed on two different cables, one feeds nearside and registration plate, the other feeds offside. Both fuses blowing suggests a quite serious wiring fault or maybe even an insulation failure due to cable overheating. Either way it needs a careful and methodical approach to find out exactly what happens and when.

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Hi,

 

What is baffling me is that the lights work fine until I connect the van onto my towbar and turn the lights on. The fuse then blow around 5 sec later.

Yet if left connected without being hitched onto the tow bar the lights remain on!!!!???

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21 minutes ago, Solderjoint said:

Hi,

 

What is baffling me is that the lights work fine until I connect the van onto my towbar and turn the lights on. The fuse then blow around 5 sec later.

Yet if left connected without being hitched onto the tow bar the lights remain on!!!!???

Does seem odd. I would get a multi meter and test both plug and socket and make sure there is no inappropriate contact between any "pins" and any pins and "earth"

 

macafee2

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Hi,

 

What I did do earlier today is to remove the 2 earth/white cables from behind the bumper. They are connect onto tbe body eith an 8mm bolt, I removed paint/debris to bare metal and reattached bolt. 

Not had chance to try the van again due to running out of time. I also have a new 12N socket to install, fingers crossed.

Realky hoping this earth refix will cure it!!

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1 hour ago, Solderjoint said:

Hi,

 

What is baffling me is that the lights work fine until I connect the van onto my towbar and turn the lights on. The fuse then blow around 5 sec later.

Yet if left connected without being hitched onto the tow bar the lights remain on!!!!???

That's because the fault is more likely to be in the caravan than the car!

Edited by Stevan
  • +1 1

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Hi Stevan,

 

Have you got any ideas for me to try? Ultimately I will get both looked at if I must it would be good and cheaper if I could sort it myself!

What is the difference from the car lights on and working then tow bar connected and they fail... ! What am I missing?

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Without connecting the towbar, you could run a wire or connect with something metallic between the caravan hitch and the towbar to see if this gives the same problem - if so then it might suggest a bare wire touching the hitch metal/caravan chassis and then getting earthed to the car. I think caravans do not use the chassis as a 12 volt system earth like cars but instead run earth wires to the various lights. Also with the 12N connected but not the hitch, move the 12N cable around to see if this causes the fault.

 

I would carefully examine the 12N cable all the way from the plug in to the caravan and see if there is any damage/loss of insulation and where it touches any metal parts. It might be you need to replace the complete cable from inside the caravan to the plug.

 

The 5 second delay might be due to the grease on the towball being moved as the hitch settles down to reach the ball metal - assuming it is greased since your profile shows a 2002 caravan.

Edited by Paul1957

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When the lights are working with the van unhitched, the earth return path is through the 7 core cable. When you hitch up, there is another earth path through the hitch. It looks like this alternate earth path is a better connection than through the wire - indicating at best, that there is a poor earth connection between the cable and chassis earth. There is obviously a short circuit somewhere too, that only shows itself when a proper earth connection is made.

 

Poor earth connections on automotive lights can result in some weird results, as there are many different paths the current can take. 

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Most likely the fault is a stray strand of wire within the 13N plug on the caravan. Also worth checking the lead from the 12N plug back to the connection block in the van.

I would open up the 12N plug and do a visual inspection.

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Hi All,

 

Thank you for your comments it is much appreciated.

I have checked the 12N plug earth with a multi meyer in ohms on 20.

Whilst holding the black test lead on the earth (no. 3 pin) and then touching each other pin with the red lead. The readings range from 0.5 upto 1.4 ohms.

Am I correct in thinking that these results mean the earth path back is ok?

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With your meter put a probe on one of the caravan sidelight terminals then the other. There should be no continuity as they are two separate circuits. If there is some continuity then I’d be looking for the cable being chafed through as it passes along or through the chassis rail or any metal part attached to the chassis and both sidelight wires making earth. . This will blow the fuse as all the while the caravan is off the towbar the earth path through the bulbs is correctly through the return earth wire. As soon as you connect the towbar the car sees it as a direct short and pops the fuses Prove it by checking continuity from the sidelight pins to the hitch head. I think you’ll find it very low or a dead short. 

Edited by Tuningdrew

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14 minutes ago, Tuningdrew said:

With your meter put a probe on one of the caravan sidelight terminals then the other. There should be no continuity as they are two separate circuits. 

Surely there will be continuity if all is well, but with several Ohms resistance, as both bulbs share an earth connection!

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41 minutes ago, Stevan said:

Surely there will be continuity if all is well, but with several Ohms resistance, as both bulbs share an earth connection!

Yes of course you’re  right. Wake up TD!! Still check for continuity through to the chassis though. 

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1 hour ago, Solderjoint said:

Hi All,

 

Thank you for your comments it is much appreciated.

I have checked the 12N plug earth with a multi meyer in ohms on 20.

Whilst holding the black test lead on the earth (no. 3 pin) and then touching each other pin with the red lead. The readings range from 0.5 upto 1.4 ohms.

Am I correct in thinking that these results mean the earth path back is ok?

 

You need to remove all the side light and marker light bulbs first, otherwise you will be reading the resistance of the bulbs. Your test has shown a continuity from the power side to the earth side, probably via the relevant bulbs,  but it may be that there is a short circuit from the power side to the actual caravan chassis which is blowing your fuses. 

 

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We seem to be coming up with two separate theories, one is that there could be a short to the caravan chassis, connecting to the car frame when hitched, the other (mine), that the short is between the feed to the lights and the caravan earth.

Plugging in to the car without hitching should narrow that down. 

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Sounds like something silly if the plug has no issues with it's wiring . As said drop the light covers on the caravan and check the earthing on the lights and number plate light then try connecting the caravan and then add a bulb at a time to see it it blows a fuse .

 

Could be the stop and tail bulbs put in reversed ?

 

 

Dave

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Electrical fittings are not really earthed as many of the materials in caravans do not conduct electricity.  12v caravan wiring usually has wires for both positive and negative, unlike the car where the negative is provided by the bodywork or "earth".

 

From the symptoms described, the positive feed to one of the two sidelight circuits is probably making contact with the caravan chassis.  The most likely place for this to happen is the cable run from the hitch to the fuses inside the caravan, usually at the front of the body.  Check for any physical damage to the cable where it runs along the A-frame.

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5 minutes ago, DACS said:

Electrical fittings are not really earthed as many of the materials in caravans do not conduct electricity.  12v caravan wiring usually has wires for both positive and negative, unlike the car where the negative is provided by the bodywork or "earth".

 

From the symptoms described, the positive feed to one of the two sidelight circuits is probably making contact with the caravan chassis.  The most likely place for this to happen is the cable run from the hitch to the fuses inside the caravan, usually at the front of the body.  Check for any physical damage to the cable where it runs along the A-frame.

 

The back plates are usually earthed or negative feed and screwed to a aluminium panel that is fixed to the chassis possibly ?

 

Dave

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55 minutes ago, CommanderDave said:

 

The back plates are usually earthed or negative feed and screwed to a aluminium panel that is fixed to the chassis possibly ?

 

Dave

I think that you will find that most caravan light fittings have two wires and do not rely on the structure they are attached to for their negative connection.

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Our handbook has a wiring diagram that shows the 2 wires to each light with them originating from the 13 pin plug.

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