Prado/Caravan park lights keep blowing fuse

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

Rockape
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?

teege

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.

Teege,

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.

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?

Cheers

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.

Ken

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 plug...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..!!!

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.
Ken

..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...

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)