simple fuse question

[ovlov]

if a fuse blows consistently, theres a short in the system correct? i just need to trace down where the short is and replace that section of wire?

what if when you try to put a new fuse in, it blows immediately? i haven't even been able to put the fuse in fully and it blows. how do i go about remedying that?

[SoCal Driver]

Depends. What circuit is this?

[adrian jaye]

HI ovlov.

ok, a fuse's primary function is to protect the wiring, its secondary function is to protect the "item".

eg. if a "item" draws normally 3amps you'd usally have the associated cabling able to provide more than that say 5amps. You may use a 3amp fuse as a minimum but no more than a 5 Amp.

The idea is if the "item" fails, it can fail one of two ways, open circuit or short circuit. If it fails as a Short (or say if the cable has been crushed and it causes a short) the Item which has resisitance will still continue to draw current.

However, if it is a dead short, it will try and draw as much as it can depending on the source, so in theory the current can be (in a car) as much as the battery can provide, 100's of amps.

Of course what happens is the cable if it is only rated at 5amps, will tend to burn if that is exceeded due to heat/resistance. Of course the bit of kit can as well, but primirily its to protect the cabling.

A good car example is the lighting circuit. (lets assume)
the front lights, are say fused at 16amps, the cables are of a specfic size (bigger cables more ability to provide current safely) so the size is due to cost and normal operation, lets say the cable is rated at 20amps.

under normal circumstances any short will blow the fuse, protect the ciruit and the cabling. however, lets say you fit thoes fcuk off powerfull lights of death, to the same circiuit.

The circuit may now try and draw more current than it was designed for. and if it tries to draw more than what the cable is rated AND if the fuse is say the wrong value (higher say 40 amps) then as the cable draws more current , it gets hot and could catch fire.

that is what in essence a fuse does.

SO.... as you have not said what your problem is. and as So-cal correctly asked. You have various possible combinations

1> The circuit you are having the problem, for some reason has a fuse of TOO low a value and is blowing incorreclty, replace with the correct value and bingo

2> The circuit has the CORRECT value fuse, and there is a fault either with the ITEM or the cabling, this is more than likly a short ! in whioch case it needs to be located.

Dont be tempted in using the wrong fuse HIGHER as you can ave serious problems,

holla back with EXACTLY what problem you have, what you have done so far and what "you" think happened before this fault occured

HTH

A

[ovlov]

sorry i didnt respond a month ago, i just started college and forgot about a lot of things.

i'm having problems with the left (ds) low beam fuse, the cigarette lighter and assoc. items fuse, and one other that i cant remember off hand (the ext. mirrors didnt work, but that might be the same fuse as the cig lighter).

i replaced all the bad fuses in the box, and everything worked until i turned on those certain items. now when i try to replace the fuses, they blow instantly. i cant put it in for 2 second to try the accessory. it blows while still in my fingers.

[VT944]

You have a dead short to ground somewhere in the protected circuit OR a faulty device within the circuit causing a short.

Look at the list of items that fuse protects listed in the fuse box (a wiring diagram doesn't hurt, sometimes every item covered in the circuit isn't listed on the fuse box cover, but usually it acts as a good enough guide) and go one-by-one unplugging each item (headlights, cigarette lighter, etc) until you can put a fuse *of the amperage rating listed on the fuse box* (sounds like you've been doing this) in the box and it doesn't blow. Only one item at a time. You'll probably need a small box of fuses, but it's the easiest way to find the malfunctioning assessory.

If you go through all the accessories listed and the fuses still blow, it's a problem in the wiring. Try the disconnecting of each assessory before we go there...

Also, pay sepcial attention to the cigarette lighter. It's very easy for this to short out as the + and - for this crcuit are both exposed. Is there any dirt in the socket? I've seen these go bad and cause all sorts of problems...

Good Luck,

[Paul Glasson]

Could not put it better than Adrian and VT944, and as an Instrument Tech that's part of my job.

[ovlov]

once the hurricane lets up i'll give that a try. i knew the procedure was something like that, i just wasnt sure.

i had the same problem before in one of my volvos, i ended up just disconnecting the cigarette lighter. i think the cig lighter is the problem too. it lit once, and it never did again. so that probably blew it.