Daytime Position Light Circuit

[st87]

Hi folks,

To those who are very knowledgeable in this field, may I ask what other components are tied in with the fuse protecting the circuit for the front position lights? Currently, I have some aftermarket 7W LEDs and they look fantastic. Today, the fuse unexpectedly blew out, and after replacing the fuse, the LEDs lit up for approximately half a second before they got shut off again by the fuse blowing up again.

The fuse I'm talking about is:

20 | FR TAIL | 10A | Front Position Lights

and is situated in the engine compartment (type B ). I understand that the manual only says 'Front position lights' as its circuit, but the original globes themselves are 5W, and the fuse used is a 10A, so would there be any chance that something else might be shorting besides my bulbs (after all, they have been working fine for a while and they did flash when I replaced the fuse).

Anyone able to share some wisdom here?

Thanks in advance!

st87.

[Tasweb]

Anyone able to share some wisdom here?

I know nothing about the circuit, but a 10A fuse will do 120W at 12V so certainly sounds like you have a short somewhere!

[LEX51S]

I know nothing about the circuit, but a 10A fuse will do 120W at 12V so certainly sounds like you have a short somewhere!

This is true if there were no resistance. but every globe has a resistance. a fuse is designed to protect the cable that is used. and the component shouldnt draw more then the cable can take, the component should have a specific resistance in which determines how much current it draws. LED globes need resistors in line with the diode to create this resistance. And if the resistor fails and short circuits, yes there is a problem and will not be solved by upgrading the fuse because you will damage other components in your car. ... . not fun!!

if you remove the globes and fuse doesnt blow there is definately a problem with the globes or globe. Also keep in mind you are using 7W globes when your circuit and fuse is designed for 5W. you may have already caused damage to cabling or socket plugs already. but the fuse is doing its job and is protecting the circuit because it is blowing so you should be ok.

the resistance difference for a 7W and a 5W globe is about 8 Ohms and will pull about an extra 1.3 amps per globe. as i said befor the cable is designed to take a max 10 amps so upping the fuse to compensate for the 7W globes may damage the cabling.

Good luck fault finding!!

[st87]

Thanks LEX51S... Yeah, it's only 2W extra on a cable that was protected by a 10A fuse. I'm sure the cable itself is capable. I didn't 'upgrade' the fuse - I only replaced it with a new one with the same rating in case it was just a one-off failure.

I was under the impression that LED lights fail open circuit, but seeing that it's not exactly JUST an LED, that could be the answer. The cheap built-in regulator inside might be poorly designed to fail short. That said, it's not exactly easy to put in a resistor in-line as a simple current regulator limiter...

Still concerning is the fact that the LEDs flashed when I swapped the chip. If the reg or the chip failed short, shouldn't I not see a bright flast at all (i.e. if the reg shorted out, I shouldn't even get any power into the LED itself) but that only assumes LEDs fail open and that it really is the regulator that has failed short.

[Tasweb]

This is true if there were no resistance. but every globe has a resistance. a fuse is designed to protect the cable that is used. and the component shouldnt draw more then the cable can take, the component should have a specific resistance in which determines how much current it draws.

I wasn't suggesting the OP increase the fuse or that the circuit could handle 120W of globes, I merely tried to point out that a 10A fuse is more than enough for the expected current draw so for it to blow there is an issue somewhere that needs to be found. Good luck with that!