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Toyota Camry Fuse and Electrical Questions

871 messages,  Last post on Nov 24, 2009 at 7:28 PM

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#41 of 871 Re: electrical shortage??? [scitsailor] by user777 Jul 20, 2006 (3:16 pm)
Replying to: scitsailor (Jul 20, 2006 2:54 pm) when you have a short with very little resistance, you have maximal current flow. Voltage = Current * Resistance. The volts across the battery is 12, so as resistance decreases, current increases.   this is why a fuse rated for a given current blows.   so - you're in a situation of excess and shortage at the same time i guess.   agreed, the current is flowing in the circuit which has the short, and not as much (relative) in the circuits that are well behaved.   shify's idea to pull the over-head dome assembly is a good one. if you have a custom, non-OEM radio/amp, I'd start there myself. Replies to this message: kiawah (Jul 20, 2006 4:34 pm)
#42 of 871 Re: electrical shortage??? [user777] by kiawah Jul 20, 2006 (4:34 pm)
Replying to: user777 (Jul 20, 2006 3:16 pm) I had a short once in an old vette, found in the wiring harness the flexed between the car and the drivers door everytime it was opened. Years of opening or closing caused the failure.   Personally however with your limited symptoms, I'd look at the dome light first (easiest), unless someone messed with the factory radio.   You may want to look at the electrical schematics for that year/car (see the 'other' web site), to make sure there aren't items on that circuit that you don't realize aren't working (like a lighter).
#43 of 871 Re: electrical shortage??? [user777] by Mr_Shiftright HOST Jul 22, 2006 (9:25 am)
Replying to: user777 (Jul 20, 2006 2:27 pm) RE: Short circuit:   Maybe I'm trying to outsmart myself here.   My reasoning was not to take OFF the positive cable, just to loosen it a bit so you COULD yank it off.   Now why the positive? Well, yes, conventional wisdom says to take off the negative and this is probably good advice. But you know, either one works in an emergency. Maybe BOTH should be loosened, to give the stand-by person TWO changes to interrupt an electrical fire.   My understand of "short" is that the current falls "short" of the target, that is, it completes a circuit well before the circuit that was supposed to be completed. After all, the dome light is the end of the line, so a live wire touching ground before the dome light has completed a "short circuit" back to the battery.   I really don't believe the term is related to "short" as in "lesser amount". It's "short" as in distance, not volume.   ANYWAY-- I'm always nervous about giving electrical advice out to anyone without supervision, but if they use common sense and have a back-up plan (like two people working on it), they should be okay.   Nigel Shiftright once told me, with singed finger pointed in the air: "Destruction happens at ten times the rate of construction". Replies to this message: user777 (Jul 22, 2006 10:37 am) Mr_Shiftright (Jul 22, 2006 6:25 pm)
#44 of 871 Re: electrical shortage??? [Mr_Shiftright] by user777 Jul 22, 2006 (10:37 am)
Replying to: Mr_Shiftright (Jul 22, 2006 9:25 am) if the yanking is done without contact to the body of the vehicle and the terminal (i.e. someone grabs the insulation), which wire you pull is gonna be immaterial to the interruption of power.   but, you'll have to re-attach that positive at some point won't you? then you'll have the issue with possible shock.   short: well that is essentially a path to ground with little intermediate resistance. what is the resistance of a length of wire? there is a formula, but for most wire used in a car, it is pretty negligable.   where there is small resistance, more current must flow, hence a fuse rated for X amps will blow when sinking more than X amps. remember volts = current * resistance.   a fuse in a car, or in a house is rated such that it is the weakest point in the circuit, right? you want the fuse to blow when it senses too much current flowing. the heating which will result will cause the fuse to fail.   if the fuse were rated larger than the current carrying capability of the wire, or metal conducting parts in the destination device, guess where the heating is going to occur and where the circuit will open.   you never want to "over-amp" a fuse or a circuit breaker in your home for the given wiring. you want the fuse or ckt bkr to trip and protect the wiring and the device.   in a car: no vehicle fires please.   as to fall's short of the target, in general this statement is true, however the target (like the overhead dome light) can be the target. i understand what you are saying, the real target is the bulb in the overhead dome light. no argument there.   as far as loosening both clamps... i'm not going to give you advice shifty. you're the auto guy. me though? i wouldn't do it to either terminal. i mean to say there is a time to remove the negative and work on a circuit, and there is a time to re-connect... but to leave loose? nope. i can't see the advantage, and only see a disadvantage. let's say you got a current drain and you are tracking it down, and lets say you leave 1 or 2 loose clamps. guess where there is going to be resistive heating (happens where the amount of conductor / contact is smallest)? just like the sizing of the fuse (generally set by thickness of fuse material). guess also where there is gonna be potential arcing?   if you have a battery out-gassing...   well. maybe *i'm* over analyzing the problem now. Replies to this message: Mr_Shiftright (Jul 22, 2006 6:25 pm)
#45 of 871 Re: electrical shortage??? [user777] by Mr_Shiftright HOST Jul 22, 2006 (6:25 pm)
Replying to: user777 (Jul 22, 2006 10:37 am) This discussion inspires me to install a battery shut off device!

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