SHORT? (Page 1/1)
BUFF1950 AUG 20, 05:20 PM
I have a 1987 GT and has recently developed a short that keeps draining the battery. I've charged it and when it's charging and I open the door it stops. Could it be a bad door relay, light switch, ?????? HELP!
Gall757 AUG 20, 06:03 PM
Those little plunger light switches in the door jamb can wear out. Check for bare wires.

See the Ogre's cave for the proper way to find battery drains.

[This message has been edited by Gall757 (edited 08-20-2019).]

theogre AUG 20, 11:21 PM
He Means... See my Cave, Battery Leaches and maybe Sneak Path
Second link more so if you have blown fuses too.

To speedup that...
buy a "short finder" kit and use the "meter" only. (meter will move on wire w/ loads but not "osculate" w/o the other part.)
buy/rent/etc. a DC Amp Clamp meter. is better because you see the actual load on a wire but cost more.
Both can quickly help point out a battery drain w/o cutting or disconnecting wires.

Notes:
ECM and Radio draws very low amps all the time and won't kill a good battery in hours to days.
AC only amp clamps that most have or often find at flea markets etc won't work here.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

ChuckR AUG 21, 12:33 PM
This is how I find parasitic drains. All you need is a Multimeter and a couple of clamps or other way to depress the door switch and deck switch. I am sure that The Ogre's way is probably the best way. But this is what I do.

I pop the hood, in this case deck lid, i then depress the switch that turns on the light to stop the draw from the lights there.
Unhook the negative battery cable.
connect the multimeter in series to the battery post and the cable. Make sure to use the Amp connection on the multimeter for the red line. It doesnt matter which side is on the post and which is on the cable.
Turn on the multimeter to DC Amp.
The reading should be less than an amp if there is not a parasitic drain. If you are reading higher than that you have a drain.

To find the drain:
Start with fuses in the engine bay, start pulling fuses until the amperage on the meter drops. If it doesnt then move to the cabin fuse box.

Use a clamp or a piece of tape to keep the door switch depressed. Situate the meter in your back window so you can still see it inside the car.
Start pulling fuses again. when the amperage drops you found your circuit with the offending draw. look at what that circuit is and start tracking all the items running on that circuit.
ChuckR AUG 21, 12:39 PM
Well now that I read The Ogre's, it is the same method I use.... LOL. I should have read the previously suggested options first...
Gall757 AUG 21, 08:46 PM

quote
Originally posted by ChuckR:

The reading should be less than an amp if there is not a parasitic drain. If you are reading higher than that you have a drain.

.



One Amp is waaaay too much. Most Fiero docs say 50 milliamps is the max....or 1/20th of an Amp.
theogre AUG 22, 02:34 AM

quote
Originally posted by Gall757:
One Amp is waaaay too much. Most Fiero docs say 50 milliamps is the max....or 1/20th of an Amp.

Yes, Stock Fiero everything draws a few mA when off.
Radio and ECM only needs enough power to save memory for codes presets and clock.
Gen2 HL Modules draws very little to power the one chip inside all the time. (Running Gen2 HL motors eats ~ 3a each for 1 sec max normally.)

Most standard meters barely registers these small loads reliably. Even amp clamps have trouble reading them. And that's meters set to read mA range.

over night or a few days and battery dies then have more then 1 amp. often way more.

Worse, repeatedly killing the battery will permanently damage the battery at minimum. Worse still if you fast charge it too.
Starting batteries hate deep discharge to begin with and hate fast charging when that happens.
(Deep cycle batteries take a deeper discharge but you can wreck them too for drawing too much power.)
So even if seems to work after fixing whatever... expect to replace it soon.
ChuckR AUG 22, 05:55 AM
I was being very general on parasitic drains not specifically a Fiero. Yes 1 amp is too much, but in non specific terms "less than 1 amp" i meant as if you do get a reading, then it should be lower. Most of the time however a parasitic drain is going to me more than 1 amp.

That said, OP said when they open the door it stops charging?

quote
I've charged it and when it's charging and I open the door it stops.



I am not sure how opening a door would stop a battery charger, unless I am mistaken on what Buff1950 meant there. So I am not sure if all this tracking draws is actually going to help them.
theogre AUG 22, 12:19 PM
Not sure either.
But door jam switches and footlights can have a sneak path as in my cave and does odd things when have a fuse blown.