1985 5.0l Coupe- Finding a power draw

[sarasara_95]

Hello,

I am struggling to find a power draw in my 85 Thunderbird. What is the likelihood of the alternator causing my battery to drain? I had a very rusty/corroded battery cable and replaced both cables, but my brand new battery still dies after just being plugged in overnight. I don't have accessory on at all. I do have an aftermarket radio but it has never been a problem in the past, the trunk latch has been unplugged since the 90s for some unexplained reason. The alternator was replaced in 2004, but the car was hardly driven since then (maybe 10,000 miles), is it likely that this is the issue still? The alternator charges the battery just fine, the car is just somehow completely draining the battery to nothing when it's off. My coworkers work on forklifts and there's a 50/50 split of them telling me it is the alternator and also that it isn't, is there a test I could do? I have tried unplugged the cable while the car is on but it indicates the alternator is fine, could it still be the voltage regulator on the alternator itself?

I haven't worked on this car much, sorry if this is a stupid question I am just skeptical on changing parts out unless it's necessary, that money could easily go to brakes and suspension etc as it's all pretty rusty these days, everything is OEM except for a handful of parts

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[74 Harley]

There's a lot to do here. Most likely, it's not the alternator. But it could be if one of the diodes went bad. More than likely you have a relay stuck on. Does the fuel pump stay energized after the key is off? Just one example.
For starters you need a shop manual, and an electrical test meter. Disconnect positive battery cable and connect the meter to the battery post and the cable. If you read voltage with the car off you are reading the short. Pull every fuse one at a time and recheck the cable. When voltage goes away you have isolated the bad circuit.
Do all fuses, then relays. Hopefully you find it.an alternator repair shop may be able to test the diodes.

 

[sarasara_95]

There's a lot to do here. Most likely, it's not the alternator. But it could be if one of the diodes went bad. More than likely you have a relay stuck on. Does the fuel pump stay energized after the key is off? Just one example.
For starters you need a shop manual, and an electrical test meter. Disconnect positive battery cable and connect the meter to the battery post and the cable. If you read voltage with the car off you are reading the short. Pull every fuse one at a time and recheck the cable. When voltage goes away you have isolated the bad circuit.
Do all fuses, then relays. Hopefully you find it.an alternator repair shop may be able to test the diodes.

thanks! that's definitely helpful, I did find a site that has all manuals for all vehicles between 1982-2013 and it does actually have my tbird on there, this is where I started thinking it could be the voltage regulator in the alternator. Nothing seems to be on when the key is off, like it's completely dead silent everywhere and all the lights stay off, but that is really helpful, thanks!

 

[Angelo B78]

Hello,

I am struggling to find a power draw in my 85 Thunderbird. What is the likelihood of the alternator causing my battery to drain? I had a very rusty/corroded battery cable and replaced both cables, but my brand new battery still dies after just being plugged in overnight. I don't have accessory on at all. I do have an aftermarket radio but it has never been a problem in the past, the trunk latch has been unplugged since the 90s for some unexplained reason. The alternator was replaced in 2004, but the car was hardly driven since then (maybe 10,000 miles), is it likely that this is the issue still? The alternator charges the battery just fine, the car is just somehow completely draining the battery to nothing when it's off. My coworkers work on forklifts and there's a 50/50 split of them telling me it is the alternator and also that it isn't, is there a test I could do? I have tried unplugged the cable while the car is on but it indicates the alternator is fine, could it still be the voltage regulator on the alternator itself?

I haven't worked on this car much, sorry if this is a stupid question I am just skeptical on changing parts out unless it's necessary, that money could easily go to brakes and suspension etc as it's all pretty rusty these days, everything is OEM except for a handful of parts

Do you mean the battery drains when its sitting?

 

[sarasara_95]

Do you mean the battery drains when its sitting?

Yes it drains while completely off, just overnight