Cratecruncher

I recently brought my '87 out of moth ***** and am working my way through a punch list of items to fix.

After replacing the old battery and firing it up I returned the next day and the new battery was dead as a doornail. I recharged it and put an ammeter in series with the positive terminal w/ the ign switch off: 2.6 AMPS! Geez.

I've done some preliminary stuff like pulling all the fuses individually: both underhood and driver footwell. Nothing had an effect except the 60A fuse marked "BTN" underhood. Removing that one dropped the drain current to about .5A which is still way high.

Anyone have a suggestion as to what may be causing this?

satch

iTrader: (1)

The BTN fuse supplies the battery buss fuses in the interior fuse box. These items would be the horn, flashers, interior lights for example. Thus remove the battery buss fuses one by one and see if you can find the source of the drain and remember to turn off the interior lights which come on with the door open.

Checking for a drain after the electrical circuits have been on will cause a higher drain as it takes time for them to slowly chill down. Not sure if this applies to your particular situation.

Cratecruncher

Well I already did pull all the ancillary fuses one by one and nothing had an effect except that one BTN fuse underhood. I started studying the wiring diagram and noticed that in addition to the things you mentioned, it also supplies power directly to the Logicon.

Here's something else I thought was unrelated but now I'm wondering.... While I was warming up the car I got bored and started dinking around with the fan slider on the Logicon. Playing with it caused my open door warning light to go out and the engine dropped a few rpm. Fiddling with that slider some more got everything to go back to normal. Is my Logicon possessed? Anyone have experience with shorts in these things?

satch

iTrader: (1)

The wire that is connected to the BTN is White/Red. This wire does not feed anything directly except the interior fuse box.

BTN powers 6 interior fuses.

Another thing. Maybe it doesn't matter at all, but when looking for an amperage drain wouldn't you disconnect the negative battery cable to place the multimeter in line?

Cratecruncher

Satch, I appreciate your help and now I see your point. BTN doesn't supply power to the Logicon without making a stop at the interior fuse panel. The wiring diagram I'm looking at is the 1987 Workshop manual from Mazda and they drew that leg separate from the rest of the fuses making it look as if it were an in-line. It was only after digging further into a more detailed hvac diagram I found out the 15A fuse is clustered with all the others.

I'm still digging around trying to isolate the current drain. My charge warning light is starting to glow in the warning cluster and I'm still getting odd changes in rpm when I add electrical loads. I'll keep playing around with it and keep the thread up to date with what I find. The car hasn't run in 5 years (!) and I'm afraid it's going to fix itself before I can isolate it (lol).

EDIT: Tomorrow when I have some daylight I'll look at the leg between the BTN fuse and interior fuse box and see if I can find a chafed wire or anything weird going on. While playing with the fuses underhood I had trouble getting the 80A main fuse out of the holder. It looks like it may have gotten hot at some point. I didn't dare try to pull it out until I know I have a replacement in hand. Those underhood fuses look like they may be hard to find. anyone know?

Regarding ammeter location; as long as it's in series with the battery it doesn't matter whether you count the electrons coming or going. I was always told it's the number passing through over a given length of time that's important.

satch

iTrader: (1)

Have you tried to disconnect the alternator B+ wire and check for any change in the draw.

Cratecruncher

I had a chance to do some more troubleshooting today. I tried disconnecting the B wire from the alternator and unfortunately it didn't change the draw current. I haven't completely ruled out the charge circuit yet but have been looking at ancillaries most of the day.

I found that I get 0.5A draw with the BTN fuse installed and all the downstream fuses pulled. I get the full 2.5A when the 7.5 HAZARD fuse is in by itself OR the 10 ROOM fuse is installed. All the others drop the current draw down to the 0.5A.

Looking at the circuit diagrams I tried to find some commonality between those two circuits and Bingo: both lead to the Central Processing Unit. Well I dug that thing out, pulled the boards out and inspected everything for visual signs of overheating etc. They're as perfect as the day they were made. Also with the unit unplugged I still draw 2.5A so I know thats not it.

I've run out of daylight today but tomorrow I plan to go down the list of everything on the ROOM circuit: dome lights, spot lights, etc.

I had no idea this would be so time consuming.. I expected 2.0A to be a lot easier to find than this. Worst part is that I've still got 0.5A to worry about once I find the 2.0A.

I discovered why my main fuse wouldn't pull out. It's a bolt in D'oh! After removing the bolts on either side it slid right out. With it and BTN out the battery drain was 0.15A.

I'll update the thread as learn more. If anybody wants to throw me suggestions I'm all ears!

satch

iTrader: (1)

There are 3 plugs to the CPU. Did you pull all of them?

One of the commonality between the two fuses is the alarm system, and the two fuses are located side by side in the interior fuse box also.

The Room fuse powers the radio, dash warning lights/clock, pin 3J of the ECU, alarm, and most of the interior lights except the dash lights.

The Hazard fuse powers just the turn and hazard flasher lights.

Cratecruncher

Hi Satch! Yeah, I pulled all the connectors from the CPU and laid it in the grass 12 feet from the car so I wouldn't step on it. I feel pretty good about the CPU.

I should have mentioned this in the original post. I bought the car new in 1987! It's a bare bones coupe so the electrical system is simpler than a loaded up version w/alarm, cruise, abs, automated eyebrow plucker, etc. Add to that, I'm the only one that has ever worked on the car and have never modified the electrical system other that to wire in a radar detector 20 years ago. (It was the first thing I checked, btw.)

The car's interior spot lights have been screwy for years. Sometimes they don't come on when they're supposed to so I don't realize they're on when I leave the car overnight. I've also had some issue's with the rear hatch courtesy light located on the passenger side strut so I intend to take a look at that too.

I'm still confused why I could get the 2.0A current draw through both the HAZARD and the ROOM circuit. It would seem there must be an overlap somewhere....like maybe a couple of wires are shorted together or something. I'm just guessing at this point. I'll continue trying to eliminate stuff as I work my way through that ROOM circuit. There's a ton of crap on that leg to check.

satch

iTrader: (1)

As far as the interior spot light is concerned it is limited with respect to how many wires are involved. The wiring diagram indicates 2 wires going to the unit. The Blue/Red supplies constant voltage and the Blue/White wire supplies the needed ground signal to turn the spot lights on. There should be a 3 position switch at the light. One position supplies the ground signal to turn on the light whether the door is open or not. The 2nd position turns the light on when the door is open as the door sensor provides the ground signal necessary to turn the light on. The 3rd position just keeps the ground signal from reaching the light regardless of whether the door is open or not.

The reason why I mention this is it's an easy unit to check as to why they are not working as either the problem lies within one of the two wires or the switch itself. Understanding what is preventing the light from working properly "might" give you insight into the amperage drain.

One thing you might want to do is with the plugs pulled off the CPU take a voltage reading on all the wires and compare the results to the wiring diagram and see if there are wires w/voltage that should not have it.