Caravan Tail Lights - Electrical PRoblem

Submitted: Tuesday, Mar 06, 2007 at 19:17
ThreadID: 42971 Views:3777 Replies:8 FollowUps:2
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I have a small problem with our van that I am hoping somone can help me with.

The car has been wired so the taillights on the van (rear and side) total of 14 lamps, with an estimated wattage of 100 W (i can't read the printing on the lamps) are powered from the right hand tail light. When pluged in it blowns th e10 amp fuse, which makes sense. I thought of just replacing the fuse with a larger one but when I do it does not blow but the voltage drop is so large on the thin wire that the car tail light is really dim and th evan even dimmer. It is so dim that you can hardly tell if it is on.

The only solution i can think of is to put a relay in the car which operates much like a spot light relay. Is this the correct solution? Are there others? How have others solved the problem?
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Reply By: Sign-man - Tuesday, Mar 06, 2007 at 19:19

Tuesday, Mar 06, 2007 at 19:19
Earthing problem??
AnswerID: 225667

Reply By: Richard Kovac - Tuesday, Mar 06, 2007 at 19:32

Tuesday, Mar 06, 2007 at 19:32
Hi Andrew

Nice blog site

putting a larger fuse should not cause a voltage drop?

I would be checking the earth but if that was a problem you shouldn't be blowing fuses

hopefully someone with brains will get on the site shortly and can help you..LOL

Looks like your having a good trip


AnswerID: 225669

Reply By: Gob & Denny - Tuesday, Mar 06, 2007 at 19:33

Tuesday, Mar 06, 2007 at 19:33
i would be checking each light for a problem or the connection car/van as by calculations you should only be drawing about 8.5 amps

or get a auto leccy to run some meters over the system
AnswerID: 225670

Reply By: Graham & Lynne - Tuesday, Mar 06, 2007 at 20:32

Tuesday, Mar 06, 2007 at 20:32
YOU HAVE A PARTIAL SHORT in lights when parkers turned on with 15a fuse see which ones dims the short is at the closed one to front which dims if all caravan dims short in plug or main wiring loom
AnswerID: 225689

Follow Up By: Max - Sydney - Tuesday, Mar 06, 2007 at 21:49

Tuesday, Mar 06, 2007 at 21:49
While you are checking, make sure all the cable connections are nice and firm - the cable not half broken off at any point or a screw loose. That could be at every light and the plug and socket too.

Also - check that the pins are making good contact in the plug. I once spent a pleasant evening becoming intimate with the wiring in my van, only to finally discover that I needed to put a pocket knife blade down the little split in the pins on the plug to make them all connect firmly again. Bingo - problem solved. And it was a fairly new (flat) plug.

I felt a fool.

FollowupID: 486608

Reply By: Ann 40 - Tuesday, Mar 06, 2007 at 21:27

Tuesday, Mar 06, 2007 at 21:27
i agree with earth problem,our 80 series is wired from right hand tail light and the van has 10 lights running off that and has been for 10 years with no problems
AnswerID: 225701

Reply By: Kiwi Kia - Wednesday, Mar 07, 2007 at 07:49

Wednesday, Mar 07, 2007 at 07:49
If you want to do some detective work then try this;

Remove all lamps and turn lights on and replace lamps one by one.

If the lamps suddenly go dim as you add them to the circuit then check the lamp holder where you replaced the last lamp. Do you feel a resistance from the spring contacts as you push the lamp down into the socket? The contacts should not be discoloured (dark blue or black or coroded).
AnswerID: 225747

Follow Up By: Wizard1 - Wednesday, Mar 07, 2007 at 09:34

Wednesday, Mar 07, 2007 at 09:34
One of the first investments all caravanners and 4WD owners should make is a multi meter.

Don't play around with "lamps in lamps out" but get a multi meter onto it and you will fins exactly where it is occuring as you will have a voltage difference at the fault.

I agree with the theory of poor earth, it is the cause of 99.9 % of shorts apart from loose connections that may be arcing. Putting in a larger fuse just causes the problem to move to the weakest part of the circuit and more problems.

You might need to check where your wiring goes into the rear of the trailer plug both on the vehicle and van. They do tend to come loose or break where only a few strands of copper are hanging on.

My van is 7 years old and had a hard life. I found the orginal 7 core trailer wiring was deteriorating from heat, etc. I replaced my 7 core with 5 core heavy duty for the lights, a seperate heavier cable for brakes and an Anderson plug for power. I use a large 7 pin round plug. Haven't had a problem since.

FollowupID: 486673

Reply By: drivesafe - Wednesday, Mar 07, 2007 at 10:08

Wednesday, Mar 07, 2007 at 10:08
Hi Andrew, I think you will find your own suggestion of putting in a relay is the best solution.

While I agree that one of the most common problems found on trailers and caravans is poor earth connections, poor earth connections not only will not blow fuses but because they reduce the amount of current will actually lessen the chance of a fuse blowing.

The fact that you blew a small fuse but the higher rated fuse did not blow indicates that your problem is just too much of a load on the circuit and this is also the most likely cause for the voltage drop.

First off, the existing circuit is designed to cater for a given load and is protected by a suitably sized fuse, you should NEVER replace a blown fuse with a bigger one than the one that was intended to protect that circuit.

In worst case situations, you can have a fuse in the circuit but because the wiring is so thin, it can not carry enough current to blow the fuse and the cable simply heats up and catches on fire. So stick to the correct fuse.

Next, put on your glasses and read the wattage on the globes. This is not meant an insult to you, you MUST know the exact wattage of all the globes so you can then work out both what size cable will safely handle the current needed and give you the least voltage drop and, more importantly, what size fuse will give you the correct protection.

AnswerID: 225764

Reply By: Ray Bates - Wednesday, Mar 07, 2007 at 10:58

Wednesday, Mar 07, 2007 at 10:58
Have you consider replacing the globes with LEDs ? I did with my caravan
AnswerID: 225773

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