Electrical Problem - sparked off alternator and headlights wont turn off

[TSIsean]

Today I started an oil change like any other. I noticed that the nut that the oil filter screws onto was loose so i tried to tighten it with my 24mm wrench from uptop. I usally disconnect the battery for work in the engine bay but never when I do oil changes. I was tightening the nut and i sparked my wrench off the alternator and the head lights to turn. Only the headlights. Look inside and the switch is off, everything is normal. I pull the relay under the hood and they go out but when I put it back in there on! I did this a bunch of times and played with the switch inside and still nothing. Only way they turn off is by pulling the relay or disconnecting the battery.


Anyone have any ideas? The ligths and everything still turn on like usual with the switch inside. No fuses under the hood blown either.

Lesson of the day - always disconnect the battery no matter what your doing.

Thanks.

 

[Bostedquest]

you fused a relay.

 

[TSIsean]

Yeh figured it had to be something like that. Just replace it and i'll be all set?

 

[Bostedquest]

Yeh figured it had to be something like that. Just replace it and i'll be all set?

start with replace and move from there.

 

[TSIsean]

Problem Solved. I thought I checked all the fuses but I must have passed over the alternator fuse. It was blown. I replaced it and everything works fine.

 

[psychlow]

The blown alt fuse caused your headlamp relay to stay closed? That's some weirdness right there.

In the future, if you have a multimeter, you can test relays quite easily. A 4-pole (single pole single throw, normally open) relay will have two coil terminals and two switch terminals. You measure the resistance (ohms) between each to find out which are which - the two with the resistance of a few hundred ohms (but not zero) are usually the coil pins. The other two pins should have resistance in the mega-ohms.

If you apply 12V to the coil pins, you should get near-zero resistance (maye an ohm or two) on the switch pins. When you take away the 12V from the coil, the switch terminals should again have mega-ohm resistance.

A 5-pole relay will be similar, except they'll be 3 switch pins. Power applied to the coil pins will switch power from the normally closed terminal to the normally open terminal, and the other pin will be common for both.

When you short out a relay across the coil, it can see enough current to weld the switch together. I think that the relay fused temporarily, myself, and perhaps it coincidentally opened back up at the same time you replaced the alternator fuse.

Does taking the fuse back out cause the headlamps to kick back on?

(As a side note - sweet car, man.)

 

[GTM]

The blown alt fuse caused your headlamp relay to stay closed? That's some weirdness right there.
...
Does taking the fuse back out cause the headlamps to kick back on?

Yes, this is a common condition which will repeat if you pull the fuse. You bulb check / monitor system is on another fuse which defaults to lights on so if you are driving on a dark road and you Alt. fuse blows you won't lose your headlights. This circuit has been used on motorcycles for 25 years but has only been the last 15 or so the auto industry has adopted it.

Cheers,
GTM

 

[Defiant]

if you are driving on a dark road and you Alt. fuse blows you won't lose your headlights. This circuit has been used on motorcycles for 25 years but has only been the last 15 or so the auto industry has adopted it.

If only they'd adopt the MC turn signal scheme

 

[psychlow]

Yes, this is a common condition which will repeat if you pull the fuse. You bulb check / monitor system is on another fuse which defaults to lights on so if you are driving on a dark road and you Alt. fuse blows you won't lose your headlights. [...]

Awesome info, sir. Thanks for clarifying.

 

[GTM]

Awesome info, sir. Thanks for clarifying.

Sure thing, the bill is in the mail. It needs to be posted so people can find it or at least so the search engine adds more weight when evaluating the intent. I don't know from which year to which year this applies I do think 1st and 2nd gen are wired this way, after that I don't have info.

The bulb test circuit is one of the most complex that a mechanic will ever have to deal with for unless you understand the circuit it will play dozens of tricks on you. The ECU isn't this difficult. I don't know if a schematic exists for DSM but it does for some other cars, I think the factory manual just shows it as a box and that's it. There may be something online for another vehicle which would give you a clue how it's laid out so you could then apply this understanding to that of DSMs. A quick search of Google found nothing, I'm not about to spend 2-3 days drawing one so will have to find in some manual and post it somewhere. One of the most common mistakes is people think all the black wires are ground and will tie radio or alarms into them. Big mistake.

Cheers,
GTM

 

[boostedgst2984]

yea i had the same prob with my eclipse with i was changing the alt. it was cool t sparked the a little puff of smoke came out of the fuse