Ammeter discharge with key on

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73Scamp318

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I've been chasing an electrical problem for a few weeks and trying to get the car roadworthy for an alignment this weekend. The car is a 74 Duster that I bought last year that had been mostly disassembled, so I'm working with a basically unknown car.

Here are the symptoms, maybe you guys could give me some ideas on what to check next...

With the key turned to ON and no accessories turned on, the ammeter shows a significant discharge...about 1/3rd of the way to the first discharge mark, which is about as low as I'd expect it to drop when cranking the engine.

I disconnected the ground from the negative post on the battery and put a test light in there so I could see what was going on. Key ON, bright light. So I went through and disconnected all of the fuses..key ON, bright light.

I replaced the starter last night with a known good one because it had a dead spot anyway, but that didn't make any difference. I remember when I was fighting to get it fired the first time, I checked the voltage at the coil and I was getting about 4 volts run/6 volts start.

Where do I go from here? I have grounds from the battery to the engine and battery to the chassis, but can put in more if it might help. Any help would be greatly appreciated.
 
All of it? I was under the impression that the amp meter should not show a significant discharge with the key on and all accessories off. Isn't the coil voltage supposed to be closer to 9.0v in run and 12.0v in start?
 
You're energizing the voltage regulator as well if I remember right. All of them I have ever seen drop the needle a good bit on the other side of half way.
 
Doesnt it also depend on if the points are closed or just happen to be open when you turned the key off the last time it ran?
 
Frankly I'd bet you are imagining a problem you don't have. You have a meter with an ammeter function, that can measure 20A? Hook that up in place of your test lamp and see what it draws.

Then make sure the interior lamps and all other switches are off, and make sure the brake lights aren't stuck on. Switch on the key, pull loose the regulator plug, and unhook power to the ignition system, and I'd bet your "troubles" go away.

You have any other "maybe" loads like an aftermarket stereo?

While you are doing this would be a good time to see if you have any other unwanted loads with the key OFF. Leaky diodes in the alternator is one possibility, as well as components in a "wired hot" stereo/ amp, and corroded components in things like the interior lighting (door switches)
 
I may be imagining things, but I'd rather go through it and be sure than run the risk of frying the new harness I put in or an electrical fire.

It has electronic ignition, so no points. With the exception of the dash lights, none of the other lights are in the car yet. There's no stereo in the car and it shows no draw I can see using a test light with the key in the off position.

I'll have to dig around for a meter that reads amps, but I'm pretty sure that there's one around the shop somewhere. Earlier tonight, I tried unhooking the coil, alternator, voltage regulator, ballast resistor, and ignition ECU, but still showed a draw with the key on. I have to change out the steering wheel, so I'll have that apart tomorrow and will check the column wiring out.
 
Some of those had (forget the exact term) timed lighting device right in the ignition switch. You need to find out just how big this draw is. Double check stuff like the cigarette lighter, glove box lamp, dome lights, etc.

How about the warning buzzer?
 
I might add for clarification.... to measure current (in amps) you have to put the meter in series with your circuit, not in parallel like you would to measure voltage. A test lamp doesn't tell you much. I'd recommend you go buy a good meter, you'll use it often enough to justify the cost.
 
they all do that if you go to the ignition on side...to test unhook positive to the coil and unplug voltage regulator....draw will be gone
 
The only way to disconnect everything is to disconnect the fusible link. Dark blue with white tracer begins at ignition switch and is not fused.. It feeds ignition, alternator field, instruments, and I probably forgot something more.
 
Gauges draw power too. Trunk lights-under hood light-interior. Key hole light. Plus the factory amp gauge is not a high precision gauge or even linear.
 
Gauges draw less than an amp, I think. In any case, the gauge (temp, oil) would barely be noticable on the ammeter.

Good point about the ammeter, though. Make sure the "reading" you are "reading" is not the "natural" off center it might have when off. It's why I insist you MUST use a multimeter that is fairly accurate, at least, to see what you "really have" there
 
67Dart273 said:
Gauges draw less than an amp, I think. In any case, the gauge (temp, oil) would barely be noticable on the ammeter.

Good point about the ammeter, though. Make sure the "reading" you are "reading" is not the "natural" off center it might have when off. It's why I insist you MUST use a multimeter that is fairly accurate, at least, to see what you "really have" there
Click to expand...

With the original mechanical limiter and during initial switch on ( warm up period ), the current flow is relative to the fuel level.. That limiter will pass as much current as it can until the needles reach intended positions. Afterwords the draw is reduced.
I guess the most severe draw at switch on I've seen would be a internal short at the alternator. Easy test is just pull the blue wire off of it.
 
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