Electrical Unused Fused causing intermittent drain?

[Mr_Q]

Got out my test light tonight and found some answers! (1993 Mustang GT Convertible)

I have two fuses that are pulling quite a load. Illuminates the light nice and bright.

HOWEVER....

With both of those pulled (highlighted in red) I would get the light to come on for about 2-seconds, then it would fade out to a super dim, barely on pulse. When I finally pulled the suspect fuse the test light was finally dark! That last fuse is a 20amp marked UNUSED. (fuse 17 in both charts)

Any reason it would do that?

Now for the real issues...

Now depending on what fuse layout guide you use below, the two fuses affect different things. I have no idea which chart is mine or if either of them are. The top one is for a 1993 Mustang LX 5.0 Convertible. The lower is for a 1993 Mustang GT. I have a 1993 Mustang GT Convertible.

The top image contains a fuse that includes Convertible Top, the lower image does not. This makes me think the upper image is my car. --but---It also says that same fuse does rear window defroster which my car doesn't have. Finally, the top chart lists (8) as a Power Window. However since this is obviously a user made chart, I think that's a typo or specific to a 5.0 LX convertible versus a GT convertible. As you see in the lower chart, for a non-convertible GT, reads Power Mirrors. As "power mirrors" is missing from the top chart all-together, this leads me to believe the top one has a typo for fuse 8.

Also the top chart lists CLOCK for 8. Well my radio isn't working with that fuse out. My fuse 11 is still in too. To clarify, both charts state radio is on fuse 11. Top chart also includes fuse 8 for "clock" whereas lower chart says fuse 8 is also "radio." I'm citing these differences as typos or simply the difference between a convertible 5.0 lx and coupe gt.

The facts are with fuses 8 and 16 pulled, my car does not have these functioning...

Door warning chime.
Horn, cigar lighter
Courtesy lamps (although I have no bulbs)
Glove box light (again, no bulb)
Engine light (after market hood, no bulb)
Clock (assuming this also means radio)
Power Mirrors

I don't have any electrical contacts or wiring around the fuel filler door. I also lack a fuel filler door release switch. My car only has one for the trunk. I mention this as both charts say fuse 8 controls this too.

With those two fuses pulled, I have no drain. Test light is dark.

 

[5.0Droptop]

Trunk light?

 

[5.0Droptop]

Cig lighter pushed in and not popping out?

 

[Mr_Q]

trunk light is the only courtesy light I have that works. it's not on unless i lift the old, verified.

 

[Mr_Q]

never tested cigar lighter. but remember I have two fuses causing drain. I'm going to disconnect the cigar lighter next and reconnect the horn. See if that fuse will then stop draining at least.

 

[5.0Droptop]

The cig fuse will be hot all the time. The one radio fuse will be hot all the time to preserve the memory.

 

[Mr_Q]

enough to make the light nice and bright?

 

[5.0Droptop]

It will have 12 volts or battery voltage

 

[Mr_Q]

I'm just using a light right now. ill have to get a meter. sucks the radio is on the same fuse as so many other systems....ugh. although I did verify the radio was not the cause. I unplugged it over night and the battery still drained. so it's one of the other systems on that fuse.

 

[5.0Droptop]

 

[Mr_Q]

yeah thats the same image I included in my post, heh. thanks though.

 

[5.0Droptop]

Yeah that is the correct 87-93 fox one.

So 17 is a spare circuit or just fuse?

 

[Mr_Q]

in both charts its listed as either spare or unused. when installed it causes a brief glow on the test light then degrades to a dim flicker. very odd. I yanked it either way.

 

[5.0Droptop]

#8 & #16 should be hot all the time regardless of key position.

If your battery doesn't go dead when you unplug these then you have something that is pulling current.

If your battery still goes dead with those out then i would replace the alternator. They can still charge and be bad. I had a 5.0 that would drain the battery overnight. After checking every circuit everything i could i realized the alternator was shorted out inside.
If you read up on it you find out that you never want to replace the alt in a ford and hook it up to a battery that is undercharged. It reverses the diode or something and cause it to drain the battery

 

[5.0Droptop]

Do you have an aftermarket radio with an amp and sub?

 

[Mr_Q]

yeah I'll know in the morning. if she doesn't start with those pulled....then its something else. The alt is new so it shouldn't be that. possible the starter solenoid is bad....the car does odd crap when trying to start....I have to key off sometimes and key on again to get her to fire.

 

[Mr_Q]

I do have an after market radio and amp but LONG AGO removed them from the circuits to track this down.

 

[5.0Droptop]

If its dead again id put money on the alt.
it happens... especially if the battery was low as in less than 12 volts when the alt was hooked up.

The solenoid either works or it don't.

 

[MFE92]

Do you have any add-on relays in the car? If so, double check that they're actually wired correctly. It's possible for them to be wired so that they "work", as in they power the circuit they're supposed to switch, yet put a light drain on the circuit at all times, even when switched off. Ask me how I know

 

[Mr_Q]

No relays I am aware of. Car is stock.

The battery WAS dead again this morning. (down to 10volts) and needed a jump pack to start. Although, like always, it used almost no power from the jump pack to do so.

Would a bad alt not cause the test light to turn on? I had a NO LIGHT test light situation last night and was thrilled. Then this morning it's dead. How am I to test for drain if the tools I have say there's no drain???