Help finding a short

[MuscleCar91]

Hey guys I'm really frustrated with this short I have. Here's what happened I was messing with my brake pedal because it wouldn't come up enough to turn out the brake lights, I had the key turned to the left so I could listen to the radio well I lifted the pedal somewhat hard because I was getting mad and when I did that I blew the ac/acc fuse the radio went out which is how I noticed. Any ideas on what could of done this? I am sure it's the brake but what wire or where to check is my question...

Thanks,
Nick

 

[sixgunrunner68]

Look to see if there are any wires that cross in front of the pedal arm and linkage. Maybe you pinched one when you pulled the pedal up. If so it should be fairly obvious.
If your radio is aftermarket depending on who/how it was wired in, there probably is a wire haphazardly routed.

 

[meepbeep69]

I bumped the turn signal blinker box and it fell off and onto the metal dash and laid right into the opening. I did not realize it but kept blowing fuses until I got under and found it. Now it is wrapped with some tape.

Just look around.

 

[MuscleCar91]

Thanks guys i did find a random speaker wire not connected to anything with about 1" of wire exposed, not sure if that would cause it or not since it should of blown the fuse built into the radio? The search continues lol...

 

[MuscleCar91]

Well I learned something today, that there are different types of fuses lol. Guess I was using low amp 20 instead of high amp 20? Or something like that. So the low amps kept blowing because they couldn't take it. Replaced with the right fuse and my lights came on whoopie except for one thing I don't know if this has always happened but when my radio is partly out it sparks where it touches the metal dash... But when it's all the way back it doesn't assuming the piece of metal that holds the radio up is a ground? Any clues on that? There was a wire rigged into the fuse that blew that went from the radio, I didn't place back in it maybe I should...

 

[Jim S.]

Well I learned something today, that there are different types of fuses lol. Guess I was using low amp 20 instead of high amp 20? Or something like that. So the low amps kept blowing because they couldn't take it. Replaced with the right fuse and my lights came on whoopie except for one thing I don't know if this has always happened but when my radio is partly out it sparks where it touches the metal dash... But when it's all the way back it doesn't assuming the piece of metal that holds the radio up is a ground? Any clues on that? There was a wire rigged into the fuse that blew that went from the radio, I didn't place back in it maybe I should...

I think what you are dealing with are fast and slow blow 20 amp fuses. Also I don't remember if the radio has it's own wire which goes to ground or not. If it does, then yours is not connected. If it doesn't, then you are just completing the circuit to ground with the radio chassis. That is why you will see a small spark........

 

[MuscleCar91]

Well I learned something today, that there are different types of fuses lol. Guess I was using low amp 20 instead of high amp 20? Or something like that. So the low amps kept blowing because they couldn't take it. Replaced with the right fuse and my lights came on whoopie except for one thing I don't know if this has always happened but when my radio is partly out it sparks where it touches the metal dash... But when it's all the way back it doesn't assuming the piece of metal that holds the radio up is a ground? Any clues on that? There was a wire rigged into the fuse that blew that went from the radio, I didn't place back in it maybe I should...

I think what you are dealing with are fast and slow blow 20 amp fuses. Also I don't remember if the radio has it's own wire which goes to ground or not. If it does, then yours is not connected. If it doesn't, then you are just completing the circuit to ground with the radio chassis. That is why you will see a small spark........

That may have been it. I was using skinny filament ones not the fat ones that are skinny in the middle.

The radio is aftermarket so i'm not sure i thought it was grounded through the antenna...
I though i had it fixed since everything was working right Friday and Saturday morning-afternoon, So we went to a car show, it started sprinkling when we left i turned on the wipers and nothing... Opened the fuse box blown again put a new one in and it blew again... luckily it stopped raining but turning on the lights when i would use the brakes got annoying lol... Now i gotta get some more fuses and work on it some more... :brickwall:

 

[A31PKG]

I would remove the radio to get it out of the equation. There may be an issue with the radio wiring/installation. I have seen after-market radio harnesses come into contact with components under the dash and cause shorts. The area under the dash where the radios "live" in these vehicles, is rather small making even a factory radio difficult to install. So, start fresh. Get all the after-market stuff out of there and carefully inspect the harnesses, possible wiper linkage contact, etc. Also, once the radio is out, you can see up in there much better. Over the years these cars had radios, gauges, and who knows what else installed, and many a poor harness has seen better days as a result....

 

[MuscleCar91]

That's not a bad idea, Even wonder about plugging it in another car. Now your saying to take out the entire radio harness right?

 

[MuscleCar91]

Question, I found a yellow wire exposed near the hub or whatever the things called that plugs the harness into the radio. Anyways I put my multimeter on it and the negative on the on the dash where the cut out for the radio to slide in and it got numbers bouncing around. Assuming I used the meter right that should not happen? That means something is grounded to the dash that shouldn't be?

Edit
Found something that intrest me. I removed the cover under the steering wheel colum and saw this round fuse box thing between the steering wheel and the ignition, Laying on the inside of the dash 3 wires connected to it, looks like they go to the ignition? But the wire color is the same as the one on the brake pedal switch, it don't go to that does it?

 

[A31PKG]

round fuse box thing

A flasher?

 

[MuscleCar91]

Maybe looks like there is a holder on the inside of the dash for it to sit in but I covered it in tape just incase. Now my dad was messing with the fuse box and one of the ones that keep blowing read 25 or 26amp so do you think I should put a 30 in? Or is something not right.

 

[A31PKG]

Something is definitely not right...

What circuits are you referring to? In other words, which fuses are blowing? I believe you said the wipers, radio, and brake lamps...correct? To prevent a fuse from blowing, you need to isolate and correct the problem...Never increase the amperage of the fuse!

 

[MuscleCar91]

If I remember right (not infront of the fuse box) it was the middle two fuses. I took the radio out but left the harness there, put a new fuse in, turned the key and snap it blew... So I guess if it is the radio harness it doesn't matter if it's plugged in... I'm thinking tomorrow I'll trace the wires that plug in behind the blown fuses and see if I find anything.

Side note I tore into the a/c heater switch panel above the radio. the previous owner rigged the heater to a toggle switch in the glove box so i assumed nothing would be in the panel but I see alot of wires and the levers are connected to the switches so I wonder how hard it will be to fix it...

 

[A31PKG]

Go to the reference section and download the wiring schematic manual....It will guide you through the circuits. On page 6 is the fuse box. Of the 2 middle fuses, the left one services the a/c, & rear defogger (if equipped) the right one services the emergency flasher and dome light. Trace the circuits until you locate a damaged or pinched wire that could be causing the short. I did not realize your car had a/c....that adds a whole 'nuther level of complexity to the diagnostic process...Especially if someone's been in there before... Good luck with it!

 

[MuscleCar91]

Go to the reference section and download the wiring schematic manual....It will guide you through the circuits. On page 6 is the fuse box. Of the 2 middle fuses, the left one services the a/c, & rear defogger (if equipped) the right one services the emergency flasher and dome light. Trace the circuits until you locate a damaged or pinched wire that could be causing the short. I did not realize your car had a/c....that adds a whole 'nuther level of complexity to the diagnostic process...Especially if someone's been in there before... Good luck with it!

Thanks A31PKG, I'll go print them off. Yea the ac is no more. So of the middle two don't control the radio which I see in the fuse box the first one is suppose to then mine must be rigged up to them if the radio won't work with the 3rd one out... As do my brake lights.

 

[MuscleCar91]

Well looks like we may of found one of the problems. The brake light switch in front of the pedal! Which makes sense, since the brakes what caused the blow. Covered it in tape put it back in turned the key and the fuses didn't blow. So after we thought everything was all good I installed the radio and decided to turn the key to hear the radio, well i blew the RR A/C ACC fuse. Now I am looking at the diagram (thanks again) and see it should only control the; rear window washer which i don't have, rear window defogger I don't think I have that, and the ac switch I assume that is the switch above the radio?

 

[A31PKG]

The fuse boxes were designed for other models besides the Road Runner... Sedans, station wagons, etc... So there may be a feature or two that does not apply to your car... At any rate, if the A/C fuse is blowing, and if we assume (for the sake of discussion) the A/C wiring is not at fault (since you said the A/C was not installed, you would have no need to turn it on anyway), then it is possible that someone tapped into the circuit. First look on the back side of the fuse box. You'll see unused male spade terminals along the bottom. These terminals can be used for accesories. Some are switched (ignition on/run) and some are unswitched (power all the time). It is possible that someone used the A/C accessory terminal for radio power? If so, follow the wire and inspect it for damage. Also of course, the radio could have an internal issue, or perhaps it simply draws more current than the A/C fuse can handle. I know you eluded to this before, and in this case - if all else is ok - then increasing the fuse amperage would be appropriate. Determining the correct rating is the challenge. Do you have the manual for the radio? I can't imagine it drawing more than 15 or so amps....

 

[MuscleCar91]

Well looking at the back of the box I see two wires that appear to be non original. One is on the a/c acc fuse and it goes to the electric choke on the carb. The other is on the on the dome flasher fuse which looks to be the hot wire for the radio. The radio has a built in fuse and two in line fuses, one of which is right behind the box and they all appear to be fine.
Could there be something with the eletric choke? I'll trace the other two wires for that fuse a green one and a black one looks like they go to a group of wires running to the driver side.
Ok so here is what I figured out the top wire on the ac acc fuse goes to the choke and the other non original wire is in the top of the flasher fuse and it goes to the radio memory.

 

[A31PKG]

Sounds like you're onto something! Try disconnecting the electric choke and see if that solves the problem. Also if the audio unit has an inline fuse, then your best bet is to connect it directly to the power feed wire for the factory radio. Just make sure the amperages match...If you can't find matching fuses, make sure the inline one is more than the one in the fusebox.