What’s the likely culprit?

[Steve McMahan]

I’m at the start of trying to find an electrical issue. I’ve got something draining the battery when everything’s off. I’ve already pulled each fuse with no change (I’m using the test light in series with the battery negative to test for current flow). I’m hoping some of you have the list of likely culprits to test in order of likelihood. BTW, to make clear what I’ve tested, I tested both door switch for the lights, and the headlight switch is pulled out. Of course, adding to the potential issues, is I’ve created a new ECU harness that’s plugged into the main harness under the hood. I’m going to pull the power to it to check that.

If you guys could help me before the parties start, I would be much appreciated! Steve

 

[Steve McMahan]

I’m at the start of trying to find an electrical issue. I’ve got something draining the battery when everything’s off. I’ve already pulled each fuse with no change (I’m using the test light in series with the battery negative to test for current flow). I’m hoping some of you have the list of likely culprits to test in order of likelihood. BTW, to make clear what I’ve tested, I tested both door switch for the lights, and the headlight switch is pulled out. Of course, adding to the potential issues, is I’ve created a new ECU harness that’s plugged into the main harness under the hood. I’m going to pull the power to it to check that.

If you guys could help me before the parties start, I would be much appreciated! Steve

 

[Steve McMahan]

Ok, so I’ve got an update: I’ve narrowed the issue down to this area in blue. This is an electrical diagram from the Ford 1987 TBird, which is the drivetrain I’ve swapped into the Stang (see my build page if you want to know more).



I disconnected everything from the main positive post at the solenoid and connected each fuse link circuit unit; all were good except the one I marked. I was able pull one of the two plugs and when I did, the circuit went inactive. So, with the unlikely “I’ve put a screw through the harness”, is it likely the Alternator?

Thanks, I hope it is, because that means I didn’t screwup the initial wiring job (gonna count that as a win, if it’s the Alt). Steve

 

[Steve McMahan]

Final update (and you can get back to the party): the plug I unplugged from the Alt was the one for the regulator (my Alt has an integrated regulator, but it is replaceable). So, it’s a 2G Alt and I know from past threads how many of you consider them a fire hazard, but setting that aside, it’s $25 (Motorcraft) for the externally mounted, integrated regulator, and $90 for a new Alt that includes the regulator. Is it worth buying the regulator over the both? I only ask because I don’t know the history of these systems. Any history would help. Thanks again, sorry for the quick questions, I wanted to get answers before that shot of courage hit. Steve

 

[MikeGriese]

It's possible one or more of the diodes have failed. Should be easy enough to take the alternator in to a parts store and have them test it.

 

[Hemikiller]

Start where all your power feeds are connected, disconnect everything and check for a drain one at a time. I've had bad alternator regulators cause a drain.

 

[Steve McMahan]

So, I pulled the Alt, took the cover off, and one of the commutators was so notched by the brush, its toast. And I was wrong about the connector, it was the lower half of that diagram’s connector that eliminated the issue. So, new Alt is ordered.

 

[Steve McMahan]

Ops, somehow I made two threads of the same issue. I don’t know how to close this one, so I hope someone does.

 

[Cleveland Crush]

About how long does it take to drain the battery Steve?

 

[Mister 4x4]

Ops, somehow I made two threads of the same issue. I don’t know how to close this one, so I hope someone does.

I merged the two threads so you don't lose any of your content.

 

[Steve McMahan]

Thank you. I never really timed the battery loss, but when I connected the test light up in series to the battery negative post, it was brilliant white. So, I suspect it was a bad short through the Alt brushes or somewhere in the Alt. Disconnecting that harness plug at the Alt (of the two) and the light was off. All other positive battery sources check out so far., I.e., no shorts and no light.

Now go pack to the party, and thanks for the questions. Steve