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Discussion Starter · #1 ·
I've got 2 electrical issues that I need some help pinning down.

I picked up a 93 Cobra back in December. About a month after I bought it the battery went out (it was original). So I picked up an optima red top.

The car doesn't get driven very much. After sitting 2-3 weeks the batter is dead. (alarm on OR off) This has happened a few times. I'm thinking it could be the alarm, aftermarket guages, or MSD boost retard. All done by previous owner. I've got a digital multi-meter. How do I check to see what's draining my battery?

The boost retard is mounted inside the front left fender & has seen moisture due to the location. It's also wired directly to the battery. Is this right?

Recently, even with driving it once a week the battery will go dead. I think the alternator is going.
The alternator seems to not be charging my battery very well. Car barely started today (low bat) & I ran it for a good 20min. reving a little. I went to start it right after & it was only a little better. It's putting out 14volts, but I think the amperage is dropping off. Future plans include a 3G, but I'm low on funds...aren't we all!

Any info appriciated!
-Shaun
 

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The car doesn't get driven very much. After sitting 2-3 weeks the batter is dead. (alarm on OR off) This has happened a few times. I'm thinking it could be the alarm, aftermarket guages, or MSD boost retard. All done by previous owner. I've got a digital multi-meter. How do I check to see what's draining my battery?

With the car off, disconnect either battery cable and check the amperage draw between the battery post and the cable. Your computer, clock and alarm will draw with the car off, so pull the fuses for these items first. Before you do, record what the draw is for each. Now what do you have? If you still have a current draw, continue to pull fuses on at a time or disconnect things until the current draw drops. This fuse is for what circuit?

The boost retard is mounted inside the front left fender & has seen moisture due to the location. It's also wired directly to the battery. Is this right?

This item should be switched on with the ignition switch, not wired directly to the battery.

Recently, even with driving it once a week the battery will go dead. I think the alternator is going.
The alternator seems to not be charging my battery very well. Car barely started today (low bat) & I ran it for a good 20min. reving a little. I went to start it right after & it was only a little better. It's putting out 14volts, but I think the amperage is dropping off. Future plans include a 3G, but I'm low on funds...aren't we all!


If after the above checks you are still questioning the alternator, you can do a couple of things. You can bring the car to a shop that has the capability to measure the alternator's output. You may want to go through the test routine outlined in the Ford shop manual. You may simply want to put on all the accessories with the car running and measure the battery voltage at the posts. Can the car maintain battery voltage or higher? At what RPM?

Mitch
 

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Discussion Starter · #3 ·
Thanks Mitch.

I've tested the alternator volts & it pumps out just over 14 at idle. Reading over the archives, it could be a bad diode on the alternator, or a bad regulator.

I'll definately re-wire that boost retard....even though I don't use it!
 

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I've tested the alternator volts & it pumps out just over 14 at idle. Reading over the archives, it could be a bad diode on the alternator, or a bad regulator.

I'll definately re-wire that boost retard....even though I don't use it!
[/QUOTE]

Check for current draw. I think you can check the alternator (regulator and diodes) on the car following the shop manual. For a quick test, with the car running and all accessories off, check for AC voltage at the battery terminals. If your diodes are good, you should get nothing more than what's called DC ripple voltage. This will show up as less than one volt on the AC scale.

Mitch
 

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Discussion Starter · #5 ·
Test results:

Digital multimeter:
0.10 amp draw w/alarm disconnected & hood light pulled out.
0.78 amp draw w/alarm disconnected & hood light on.
0.11 amp draw w/alarm connected (on & off) & hood light out.
2.18 amp draw w hood light on & dome/hatch lights on.

Tested with a light stick (screwdriver w/bulb inside):
VERY dim with hood light out & alarm on/off.
Bright with hood light in.

So, it looks like nothing is draining my battery. Next step is to have the alternator checked.
 

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Test results:

Digital multimeter:
0.10 amp draw w/alarm disconnected & hood light pulled out.
0.78 amp draw w/alarm disconnected & hood light on.
0.11 amp draw w/alarm connected (on & off) & hood light out.
2.18 amp draw w hood light on & dome/hatch lights on.

Tested with a light stick (screwdriver w/bulb inside):
VERY dim with hood light out & alarm on/off.
Bright with hood light in.

So, it looks like nothing is draining my battery. Next step is to have the alternator checked.
[/QUOTE]

0.11 Amps might not sound like a lot, but it is. After one week, you have removed almost 20 A/hr of reserve from your battery. Almost 60A/hr after three weeks. Some batteries do not even have a 60 A/hr capacity. 500 milliamps is a lot and that's not even half of what you are drawing. Just out of curiosity, disconnect your alternator. If you have a bad diode, allowing reverse flow through the alternator, you should see the amp draw drop.

Mitch
 

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Discussion Starter · #8 ·
Found it!
They had the electric fuel pressure guage hooked up at a 12V constant. The #12 in the fuse box (convertable top).

Now it reads .02amp draw.
Thanks for your help!
 
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