Fuse blown after FM modulator installation

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sdcrym

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Fuse blown after FM modulator installation -- UPDATE

I figured installing the FM modulator myself wouldn't be too big of a challenge, and it wasn't really, or so I thought. After I started the car up, the CD player didn't work and the cig. outlet didn't work. Sure enough, the 15A fuse for the cig. lighter/radio had blown.

I bought some wire taps from radio shack to power the modulator from the power line of the cig. lighter. It took me a while since the space was cramped, but I eventually got that on OK. Actually, I screwed up the first time I tried to tap in, since as I clamped down on the tap, the modulator power line slipped out. So now I have one tap clamped on to the cig. power line with nothing attached, and another tap hooked correctly to the FM power line.

I was getting kind of impatient by this time, so here's where I may have messed up. I wasn't really sure what to do with the modulator ground line. I figured, since I had this whole box of the wire taps, why not just tap into the ground of the cig. lighter? After the fuse blew, I'm thinking that may have caused a short circuit.

I swapped out the fuse with another, just to make sure it wasn't a fluke thing, but that one popped as soon as turned the key to the 'accessory' position.

Any advice on how I can go about fixing this, preferably without having to take the car somewhere? I would hate to have wasted my time if I just have to pay somebody else anyway.

As a side note, this car will be going on a 2.5 hour drive in about 15 min. I'm assuming that it's safe to drive, since whatever happened is isolated to that circuit. Please let me know if I'm wrong. :(
 
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sdcrym

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Any ideas at all? I'm really out of ideas here. I don't have a lot of experience with this kind of thing.
 

defaoite

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First ,what kind of modulator are you talking about.
Second of all, if it blew the fuse with the initial connection setup ,and again with the second setup, would this not suggest the fault might be with the modulator.
If you can please tell us what the current rating is on the modulator .
Connecting the ground of the modulator to the ground of the lighter's ground should have been fine.
 

sdcrym

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The modulator I installed was the Audiovox FMM100A.

Maybe I wasn't clear before. Before I started doing anything, I disconnected the car battery, just to be safe. The existing CD player and everything worked fine up until that point. I unplugged the wiring to the cig. lighter, and noticed that one of the prongs had '12V' engraved on it. I noted which wire went to this prong, and then I cut through this plastic outer wire holder thing further inside the car. Here I connected the modulator power cable, which had a '12V' tag, with the wire tap like I mentioned in the first post.

Also, here's where I decided to tap into the other of the two wires going to the cig. lighter, assuming it was the ground. The rest of the installation was pretty straightforward, with the antenna as well as the audio hookups. I kind of pushed everything back inside without screwing it down, in case there was a problem. I reconnected the battery and cranked the car up. The CD player's display didn't come on at all, and I tested the cig. lighter and it didn't work either. I checked the fuse box, and the 15A fuse for the cig. lighter/radio had blown. At this point, I replaced the fuse and then turned the ignition to the accesory position. As soon as I turned the key, I saw the same fuse pop. I checked the fuse in the modulator's power line (5A) and it was fine. I checked the fuse to the CD player's power and it was fine.

Aside from that, I don't really know what else to tell you. Thanks for any help.
 

defaoite

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on the cigar lighter the center pin is the +12v the cylinder in the ground, the other cables might be the illumination.
I take it you don't have a multi meter?
Disconnect the modulator from the car. Replace the fuse and check to see if your stereo works still. leave the cig lighter disconntected as well.
Start over. get your hands on a DVM and insure that you have a +12v point and a proper ground point attach the modulator .
You could measure the resistance to ground at the connection point before you power up.
If you don't have a multimeter, youd could just assume that the center bolt on the lighter is +12V as for ground well this should be easy just attach it to the cylinder of the cig lighter socket.
i hope this helps but if it doesn't I suggest that you find a friend that is good with electronics.
 

sdcrym

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The problem with that is, I can't really disconnect the modulator very easily. The tap-ins that I used are pretty permanent. I slide part of it over the wire to be tapped, then I slide the other wire in another part. I use pliers to crimp this piece of metal through both wires, flush with the plastic piece. There's no way to take them off. The power to the modulator I can kind of disconnect because of the fuse casing, but the ground wire is connected directly from the modulator to the wire tap.

The car won't be back in town until Sunday, so I won't be able to try anything before then anyway. :(
 

defaoite

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disconnect the +12v as you suggested ,cut the ground and use a screw connector to reconnect, because I think that it is the ground that might be the problem and with out a DVM to test the ground s there is no way to be sure. and disconnecting it is the best option.
Note you can connect the ground to any part of the cars body ,taking that its not a carbon fiber body.
Let me know how you get on......
 

sdcrym

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I've been busy the past few weeks, but here's an update.

About an hour ago I cut the ground wire to the modulator as defaoite suggested, then reconnected the CD player. So now the car is as close as possible to being back to before I started messing with it. Everything works as expected, so the short must be caused by something I did.

Now I just need to figure out what that is so I can fix it and get the modulator installed. Looking at the cigarette lighter's wiring, I assumed that the wire connected to the prong that says "12V" was the cigarette lighter power, which is why I tapped the modulator power into it. Now looking at the way the cigarette lighter is set up, it looks like the other prong is connected to the center pin. It's too cramped in there for me to be sure, though

I've been searching around to find some kind of info on which colored wires represent the cigarette lighter's power and ground wires, but I haven't found anything yet.

I'll keep searching and will let you know if there are any updates.
 
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