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Discussion Starter #1
Hi guys,

So I've been having a parasitic drainage issue on my 66 mustang and finally found the fuse responsible for the drainage. With my luck, it's the only slot that is not labeled on the fuse box. It's a 30 amp fuse. The remaining 30 amp fuses are for the A/C-heat, wipers, and coil. I've attached a picture of the fuse box. The fuse causing the battery drain goes between the Dome and Power Window slots next to ACC.

The car started fine without the fuse in place, but I don't want to drive around without the fuse b/c I don't know what it controls, especially since it's 30 amps. Any recommendations on my next step?
748851
 

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Discussion Starter #3
Duh...now I feel dumb. I didn't see that. So it looks like there's something off with the headlight wiring causing the drain.
 

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I've got a 69 and did an entire car schematic, working backward from the wire diagram. It is mostly switches (44) and lights (41). Since yours is obviously not a stock system, there is no telling what it connects to. You will need to turn on all the switches (one at a time) and identify what doesn't work with that fuse out. There are often multiple things on one fuse. I would keep a list and systematically go around the car trying to identify everything. Its a puzzle, have fun.
 

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With the light switch off there shouldn't be any power to the lights. The light switch on my 69 has an internal circuit breaker and I suppose yours does too. Perhaps the switch is not completely open, or the breaker has a high resistance path to ground.
How did you identify this circuit as a drain?
 

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Discussion Starter #7
I identified this circuit as the culprit for my drain by unhooking the negative lead cable to the battery and using the amp reading on my multimeter by hooking one cable to the negative battery cable and the other to the battery negative port. This showed that there was current flowing through the battery with the car off. So I started pulling the fuses one by one. When I pulled the headlight fuse, the reading on my multimeter went to 0. Soni knew that was the culprit
 

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That’s an aftermarket or non-original fuse panel, so it will be difficult to provide anything from afar except for general troubleshooting guidelines. Who knows the complete scope of the changes?
 

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Discussion Starter #12
So I've again confirmed it's the headlight fuse. My lights don't seem to have the dimmer option.
 

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Typically, the Ford headlamp switch controls 2 circuits... one for the headlamps, themselves, with an integral 12A thermal circuit breaker, and the other "feed" circuit with a 15A internal breaker that provides power for the following...
a.Parking and Tail Lamps
b. Horn
c. Instrument Lamps
d. Courtesy Lamps
e. Cigar Lighter
f. Stop Lights.

If I was a guessing man, I'd suspect that either you didn't block the courtesy lamp door switches when testing or that you have a "closed" brake light switch (or glove box lamp).
 

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Discussion Starter #16
Typically, the Ford headlamp switch controls 2 circuits... one for the headlamps, themselves, with an integral 12A thermal circuit breaker, and the other "feed" circuit with a 15A internal breaker that provides power for the following...
a.Parking and Tail Lamps
b. Horn
c. Instrument Lamps
d. Courtesy Lamps
e. Cigar Lighter
f. Stop Lights.

If I was a guessing man, I'd suspect that either you didn't block the courtesy lamp door switches when testing or that you have a "closed" brake light switch (or glove box lamp).
I did block the lamp door switch when testing. I don't have a light in the glove box. Not sure about the "closed" brake light switch.
 

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My lights don't seem to have the dimmer option.

Yes, I do have a dimmer switch on the floor which activates the high beams. What about it?
Your 2 contradictory replies confused him, and others is what.
 

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Discussion Starter #18
Sorry. I initially thought the dimmer was controlled by the headlights knob which you pull out. I thought dimmer referred to the ability to dim the interior lights by turning the headlight knob, an option my car doesn't have. Then I understood the dimmer to be the switch on the upper left corner of the driver floor.
 

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I identified this circuit as the culprit for my drain by unhooking the negative lead cable to the battery and using the amp reading on my multimeter by hooking one cable to the negative battery cable and the other to the battery negative port. This showed that there was current flowing through the battery with the car off. So I started pulling the fuses one by one. When I pulled the headlight fuse, the reading on my multimeter went to 0. Soni knew that was the culprit
Well you used the only accurate method. The schematic below is for a 69, but yours is similar. They probably put the 30A fuse in your aftermarket system in place of fuse#6, and also connected it to light switch B. With the light switch off there shouldn't be a drain through it, but as you can see, the clock is connected directly to fuse#6, and if any of these switches are closed you will also have a drain: either door switch, trunk, cigar lighter, map light, glove box. Something could fall into the lighter socket and cause a problem.
 

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You really need to look at the amp draw not voltage..Some cars have a 12 volt draw with a very low amp draw. Rule of thumb no more than a 10th of an amp..
do you have a external voltage regulator? Make sure you check that..
 
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