Prado/Caravan park lights keep blowing fuse

When towing caravan the 10 amp fuse for parking lights blows, sometimes it doesn't blow for quite awhile but mostly after about 10 mins. Checked van lights & no shorts apparent.
Caravan has 13 clearance/park lights. My thinking is that along with the Prado parking lights & the additional 13 lights on the van is that the 10 amp fuse is insufficient to carry the load.
Should I increase the 10 amp fuse to 15 amp rating or am I courting disaster especially when the van is not being towed & the Prado parkers would then be on a 15 amp fuse & not 10 amp as per specs.
Bob & Judy
Back Expand Un-Read 0 Moderator

Reply By: Member - Teege (NSW) - Monday, Mar 08, 2010 at 17:42

Monday, Mar 08, 2010 at 17:42
Bob & Judy
What are you towing - a B-Double caravan :) But seriously, have you checked the wiring connections in both the plug and the socket at the back of the Prado. The tail light wire might be loose in one of them. It might require some movement to short it out. If that doesnt work, why not try taking the globes out of a few of the clearance lights and see if that makes a difference. By a process of elimination you might find that one of the lights has a wonky wire. I doubt very much that the fuse is blowing through excess load.

AnswerID: 407903

Follow Up By: X_PAC6969 - Thursday, Mar 11, 2010 at 15:32

Thursday, Mar 11, 2010 at 15:32
My sentiments exactly its a process of elimination but time consuming but you have to take your time you might find the problem first up may be not
FollowupID: 678353

Reply By: Rockape - Monday, Mar 08, 2010 at 18:23

Monday, Mar 08, 2010 at 18:23

your lights are probably 5watt lamps, so 13 x 5 = 65 watts devided by 12 volts = 5.4 amps. Now add your van and vehicle tail lights and front parkers.
4 tail lights and 2 parkers, 6 x 5 = 30 watts devided by 12 volts = 2.5 amps.

Total of 8 amps, now if you have a bit of voltage drop at the van ( which I am sure you will) this maybe enough to tip it over the edge and blow the fuse.

You could get a DC tong tester and see what the actual draw is and you could check to make sure higher wattage bulbs haven't been installed on the van or the Prado.

I have changed all my clearance and tail light assembly's to Led's

Have a good one

AnswerID: 407913

Follow Up By: Member - Teege (NSW) - Monday, Mar 08, 2010 at 18:39

Monday, Mar 08, 2010 at 18:39
I don't profess to have any great knowledge in this field. But how could voltage drop increase the load on the circuit? Wouldn't it simply mean that there was less power getting to the individual globes, which would have the effect of making them dim? As I undertand it, fuses blow for one of two reasons - a short circuit, or, an overload. If you can't get the power through due to voltage drop, how can that create an overload?

FollowupID: 677822

Follow Up By: Ozhumvee - Monday, Mar 08, 2010 at 19:04

Monday, Mar 08, 2010 at 19:04
A poor connection anywhere will create voltage drop and heat which further increases the load/amps drawn which then keeps going round and round as it gets hotter to the point where the fuse blows.
With that many globes on the van the fuse would be overloaded pretty quickly before any crook connections are taken into account.
Might be best to replace some or all with LED's which will drop the required current to a fraction of what it is now.
1996 Oka Motorhome

My Profile  My Position  Send Message

FollowupID: 677827

Follow Up By: Rockape - Monday, Mar 08, 2010 at 19:11

Monday, Mar 08, 2010 at 19:11

say the voltage drops to 10 volts at the lamp by the time it gets from the battery of the car through the hitch and to the lamp.

Now it is 13 x 5 watts = 65 watts divided by 10 volts = 6.5 amps.

A lot of the wiring in a van and car is of minimal size causing voltage drop and higher current draw.

Hope this has explained it.
FollowupID: 677828

Follow Up By: Member - Lotzi (QLD) - Monday, Mar 08, 2010 at 19:33

Monday, Mar 08, 2010 at 19:33
I think Rockape is on the right track, didn't a lot of the Nissan guy's have a similar problem and had to change to leds?


FollowupID: 677833

Follow Up By: Ken - Monday, Mar 08, 2010 at 21:26

Monday, Mar 08, 2010 at 21:26
Sorry folks this isn't correct at all. The wattage of the globes is 5W. This is their power disapation at a supply voltage of 12v. At 10volts they cannot draw enough current to reach 5 watts so dividing the total wattage of the globes by 10 isn't correct.
Lower voltage = lower current

It may be there is a short circuit somewhere if the fuse doesn't immediately blow, it could be due to movement such as stopping or starting or bumps in the road. If there is nothing wrong with the wiring there is good chance the globes are more than 5w and the total current drawn is more than 10A and Teege's suggestion to take our globes is the way to go. At the same time you could check their rating.

FollowupID: 677855

Follow Up By: Member - Don M- Tuesday, Mar 09, 2010 at 08:07

Tuesday, Mar 09, 2010 at 08:07
The other, and most likely scenario is that you have a high resistance joint somewhere in the van wiring. This could be a loose connector, poor connection or moisture surrounding a joint etc. All can cause high resistance and higher current draw and consequent voltage drop.

I have a similar problem with my van/LC200 but in this case it is, in part, the LC200 wiring.

My stop lights on the van will work with one or two pushes then stop...mmmm But using the brake controller lever, they work every time.?? What the... Now, I should tell you I am an electrical engineer (retired) but this problem has me tearing out what hair I have left.

In part, the reasons are that the brake controller has wiring going direct to the 12 pin 6 to operate the stop lights. For the brake pedal, it's also pin 6 but Toyota connect to their original loom wiring to the stop lights on the truck and that wiring can't handle the load. The caravan stop lights are 12v, 21w X 4 plus a high level LED, so quite a load at 12v but...they used to work and now don't...??? I believe that I have developed a high resistance joint somewhere in the van which the heavier brake controller wiring can handle, but the Toyota wiring cannot. But do you think I can find the problem...?? I have all but rewired the van wiring and soldered joints but to no avail. By the way, the brakes work fine, they are connected via the barke controller to pin 5 on the 12 pin.

I am going to run a new, heavier guage wire from the Toyota battery via a relay operating off the Toyota tail lights and if that doesn't fix it you will read a story about a mad retiree who drove over the gap....with his new Landcruiser and 24' van..!!!
FollowupID: 677901

Follow Up By: Ken - Tuesday, Mar 09, 2010 at 17:31

Tuesday, Mar 09, 2010 at 17:31
Don, please explain how "All can cause high resistance and higher current draw and consequent voltage drop."

I don't know what sort of electrical engineer you were but obviously not one knowledgeable with Ohm's Law !
When someone invents a device that produces more current by increasing its resistance I want one.

Higher resistance = lower current draw. Any high resistance points in the circuit will mean less current drawn and will not be likely to blow a fuse. If however the high resistance causes heating of the fuse assembly and/or the insulation, resulting in a short circuit this would most likely blow the fuse.
FollowupID: 677992

Follow Up By: Member - Don M- Tuesday, Mar 09, 2010 at 21:59

Tuesday, Mar 09, 2010 at 21:59
..what sort of electrical engineer...?? Well, not a very good one, you are correct based on what I said and I'm embarrassed at what I did say, not thinking too well.

In my case, it is a very vexed issue and trying to work out what is going on with a simple multi meter is proving difficult. There is a potential short circuit with dry joints (+ & -) lying together in moisture which some of mine were,... and I can't identify more in that state, which could lead to much higher current draw due to low resistance, which the Toyota wiring can't handle and is the most likely cause of my problem... But, I can't find it and its driving me nuts. My van is stored 80km away so I can't pull it apart and methodically work through it and I have no real facilities where it is stored.

As I said, I will beef up the wiring in the Toyota and run via a relay but that goes against my training but I can't find an alternative. I will also replace the existing tail/stoplights with LED versions, as Jayco now supply and if that doesn't sort it...
FollowupID: 678054

Reply By: popper - Monday, Mar 08, 2010 at 22:22

Monday, Mar 08, 2010 at 22:22
Bob, I've had the same trouble myself. Quick fix is to disconnect the reverse wire in your plug at the back of your vehicle. Toyota sent out a how to fix sheet to all dealers for this problem.
AnswerID: 407959

Reply By: Star Bug - Monday, Mar 08, 2010 at 23:55

Monday, Mar 08, 2010 at 23:55
The fuse blowing after 10 minutes or so points to an overloaded circuit rather than an intermitent short. At 100%load it can take some hours or days to blow the fuse. You may be sitting around 20 to 50% overloaded from the delay time.

Dont be lured into upping you fuse size. It's there to protect the wiring of your vehicle. You will go from burning out fuses to burning out vehicle wiring looms.

Beg borrow or befriend someone with a meter, and check out you current draw.
AnswerID: 407979

Reply By: Fred G NSW - Tuesday, Mar 09, 2010 at 08:56

Tuesday, Mar 09, 2010 at 08:56
Could the problem be due to inferior/dodgy fuses ?????

Are there fuses and are there fuses ???

I ask this as last year during our lap, I experienced similar problems with the Triton/Jayco combination, and I only have 8 clearance lights.
After several problems in quick succession and much checking of the connections and globes, I cottoned onto the fact I was using fuses from one of those very cheap multi packs like from the $2 shops, which I had put in, along with all new globes before setting sail. Worked fine while stationary, but a few k's down the track, lights out.
Reverted to "better ???/dearer" fuses (same rating) from auto parts and haven't had the same problem since.

There are more technical/logical replies above, but just a thought for the guru's on fuse quality/correctly manufactured rating.

AnswerID: 408000

Reply By: MrBitchi (QLD) - Tuesday, Mar 09, 2010 at 09:02

Tuesday, Mar 09, 2010 at 09:02
This sounds similar to the Pajero issue. They have a habit of blowing the hazard light fuse with a trailer/van connected. The extra load of the flashers on the tow is enough to pop the fuse when you use the remote door lock/unlock.

Commonly fixed by upping the fuse to a 15 amp.
AnswerID: 408004

Reply By: Member - Cantiva Clay (NSW) - Tuesday, Mar 09, 2010 at 14:27

Tuesday, Mar 09, 2010 at 14:27
Agree you should buy fuses from somewhere reputable (?) personally I like the Jaycar ones with the little led in them so you can see they are blown although bit expensive if your chewing through fuses. I did a quick calc and say you have 5W bulbs and 13.8V your looking at 85.6W or 6.2A that should be fine unless there is other stuff wired of the circuit as they say with a bad intermittent connection which occasionally overloads the circuit or a couple of the bulbs are 10 or 15W. I would work on the problem because you want to find it now than have it become a major problem out in the middle of no-where! Jaycar make a prong tool that you stick in the fuse slot and connect to dc amps on your multimeter - it might be worth trying that - hook it up then go for a drive with someone watching the meter (you can order online: testequipment/meter leads - check is the right size for your fuses) try different combinations of connections and bulbs and check the bulb sizes (watts). Also go along as much of the wiring as you can see and look for broken insulation, rubbing, crimping and look closley at the connections and fittings for corrosion or a tiny loose copper strand or moisture. Hope this helps because if your blowing fuses you have a problem so it needs to be addressed.
AnswerID: 408056

Reply By: bob & judy - Tuesday, Mar 09, 2010 at 17:12

Tuesday, Mar 09, 2010 at 17:12
Many thanks all for your response, I think Rockape put me right.
Couple of months ago I replaced the old discoloured side clearance lamps (4) with new gear, went & checked bulb wattage & they had 18 watt bulbs plus I had replaced 2 rear lamps with 8 watt bulbs.
Have now cut down overall wattage by 58 watts, ran all parkers for 15 mins. does not appear to be a problem so far but will know better when van is on the road again.
Agree with Fred that there are some fuses out there that are sus.
Popper,I disconnected reversing wire to rear plug years ago but your point could be valid.
If problems persist's will give LED's a go
Bob & judy
AnswerID: 408086

Follow Up By: Bob of KAOS - Wednesday, Mar 10, 2010 at 07:29

Wednesday, Mar 10, 2010 at 07:29
Bob and Judy

LEDs are the go anyway because you can leave the parking lights on (accidentally or on purpose) without flattening the battery.

For the electrical engineers above I = E/R (Ohm's Law). I is the current what blows the fuse. E is the voltage applied to the circuit. R is the combined resistance of the globes, connections, switches and the wires leading to the globes. If you have a poor connection the resistance increases so the current will fall. The voltage applied to the circuit stays the same. A poor connection therefore reduces the likelihood of blown fuses.

Bob (Applying Ohm's Law as a hobbyist since age 12)
FollowupID: 678103

Reply By: X_PAC6969 - Thursday, Mar 11, 2010 at 15:36

Thursday, Mar 11, 2010 at 15:36
After reading the replies here the simple soultion is get rid of the globes u have now and get LED ones they look much better
AnswerID: 408399

Sponsored Links

Popular Products (14)