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Why you should remove the negative battery terminal before doing ANYTHING!!!!

On Nov 11, 3:48 pm, "Steve W." wrote:

Guys, guys... go get a schematic and find out if the dome light is in the same circut as the ECU. Even if it is, I don't think the changing of the bulb is what caused the problem. I do think that whatever caused the light to function intermittantly MIGHT have cused the ECU problem. Either way, if the light was working sometimes, that would tell me that there was nothing wrong with the bulb. Funny thing about light bulbs... they either work, or they don't. The filament is either complete, or it's not. It doesn't go back once it's blown. Okay, so if there's a short, it would be either in the fixture, or in the wires going to it. Furthermore, That's what fuses are for! I've done it many many times. Shorting things out and blowing fuses and replacing them again. The fuse opens the circut in the event of a short before ANYTHING gets damaged (unless the fuse is either disregarded, or replaced with a fuse of a higher amperage). And furthermore, since we're on the topic of fuses, this is the whole reason that things like dome lights and tail lights and headlights and radios and ESPECIALLY ECU's are all on thier own circuts with thier own fuses. Kind of insurance, if one thing blows a fuse, you don't lose everything at once. I do agree with the titlehead of this issue, being "disconnect the negitive before working". But this rule is mostly in place because sometimes people like to play with the wires and accidently drop the exposed end of a hot wire onto the bare frame of body of the vehicle. The result can be a blown fuse at minimum, or a small fire at most (I've been there, too). However, I regress (and conclude), the dome light bulb cannot be the reason for ECU problems. ECU's may or may not be "idiot proofed," but they are not on the same circut as the dome light, the dome light cannot cause "power surges" and niether can anything else on a vehicle, and even if anything were to happen, the fuses would have caught it. Case Closed. Go get a new ECU, and re-wire your dome light. quit griping about crap that is not relevant. The more you gripe, the more other people despise you, and the job still is not done.

Reply to
fury45iii
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Yeah, but we're talking a Nissan here! I've seenthings in Nissans I've never seen in other cars.

And, he said the glass was broken. How it even lit without burning out is a mystery!

Reply to
Hachiroku

A welder and a dome light are vastly different things. An arc welder generates a HUGE reactive voltage spike when striking the arc, and that spike can wander all over the entire vehicle and fry sensitive electronics and not-so-sensitive things, too, like alternator diodes. Standard procedure there is to disconnect the battery whenever doing any welding on the thing. Shorting a dome light will NOT generate any sort of spike. Period. You need a coil to generate spikes, coils like those found in starters, alternator rotors, ignition coils. You might as well try to generate a spike by disconecting and reconnecting the battery.

Dan

Reply to
Dan_Thomas_nospam

Hmmm, Lamp filament is a tiny coil, LOL!

Reply to
Tony Hwang

with an air core and virtually no inductance. if you have instruments that can measure any voltage spike you get from a coiled bulb filament, i'd love to see your readings.

Reply to
jim beam

I do.

BUT, you don't need one. If you have an 1141 lamp with 50 loops of

1/16" (that's estimated by eye here) about 1/2" long, you can use Wheeler's Formula:

50^2 * (0.065)^2 10.5

--------------- = ----- = 0.27 microhenries

18 * 0.065 + 40 * 0.5 28.0

That's a lot less than the hundreds of henries that an arc welder ballast will have, and it's probably small enough to be compensated for by the capacitance of the wiring, even. But it's enough that you could measure it carefully with a scope and a pulse generator, even though it's actually going to be swamped at any reasonable voltage by the nonlinearity when the filament heats up and its resistance increases.

--scott

Reply to
Scott Dorsey

I personally have seen a bunch of blown ECU's caused by wiring shorts, mostly fuel pumps, but other things too.

Sure the ECU is 'protected' by a diode, but no one sells the damn diode to replace the blown one nor do many 'authorized' places exist to fix them. Half are sunk in a block of plastic also.

I have repaired a few by using a cheap diode with a +/- 10 to 15% tolerance so they fell close to the original specs. Close enough to work.

If the dome light is on a timer, it is connected to some kind of computer....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > I was lokking thorugh the Subaru manual to find out where the thermostat
Reply to
Mike Romain

First you said that the bulb was in pieces, not that the glass was broken. Was it really broken? I have seen several times that the glass part of a bulb can separate from its socket but still hanging by the leads it may still work. And I have also seen that the ends of a broken lamp filament can dangle together and get get kind of welded together, so it works again, but usually not for long. What may kill an ECU is the very very short transients in voltage when a cirquit somewhere in the system is abruptly opened or closed, especially when it is high current (a short) and/or repeated many times. If he made a momentarily short cirquit while changing the bulb that MAY be enough. That is why with modern cars we are advised not to use jumper cables without transient suppressors.

Asbjørn

Reply to
Asbjørn

Hello:

This might seem odd to you but, newer cars use bulbs that are a specific impedance. A 2157 is the same candle power as an 1157, but the impedance is higher. That's why if you use a 2157 in place of a 3057 for argument's sake.

You'll get a check eng>

Reply to
Refinish King

excellent. and it's /well/ below any level that could /possibly/ impact the ecu!

indeed.

Reply to
jim beam

You seem to forget that the dome light is 'live' all the time using a ground as a switch.

They can have the glass fall out of the base and the loose internal connecting wire(s) can and will cause a short circuit. This happens all the time with bulbs such as the 1157 in taillights.

Short circuits can do nasty things to computers like blow the input diode 'before' the fuse has a chance to blow.

It's not like the designers of modern vehicles are just BSing when they say to unhook the negative before working on them.....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08
Reply to
Mike Romain

Hachiroku ???? wrote: \

I don't buy it. ECUs are actually *very* well protected against intermittent faults, voltage spikes, etc. (Zener diodes are a wonderful thing). 99.9% of the "failed" ECUs people pull out of cars are actually fine and the problem lies elsewhere. There's no WAY you can hurt one just changing a light bulb.

Reply to
Steve

That much is not true in all cases. Any care that has "theater fade" interior lights, for example, has them powered from a computer module (not necessarily the engine controller, but a "body controller" or some other computer module.)

And on all of THAT, I agree completely!

Reply to
Steve

Think "fuse" in this case.... unless it was one of those Chinese-made fuses from Harbor Freight... ;-)

Reply to
Steve

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