The circuit, she is broken.

April 4, 2009 8:35 AM

How can I test wiring for a car radio?

I recently purchased a used car that still has the factory radio in it. The rear speakers do not work. I dismantled a few things and took the radio out, and there were no obvious problems with the connection or radio.

Is there a device I can hook up to the wires at the rear speakers to see if they are part of a complete circuit or have a break in them?

My understanding is that there are three options: a break in the wiring to the rear, an internal failing in the head unit, or both speakers are busted and need to be replaced. I welcome advice on how to effectively test each possible fault.

I don't think using a simple multimeter to test for current would be much help, as I would still be facing the possibility of there not being any signal sent out due to a fault in the head unit. And I would prefer not to solder or crimp wires until I know for sure what the problem is, and am replacing whatever needs to be replaced.

posted by Nonce to technology (13 comments total)

You're looking at this wrong. Can you not just hook the front speakers up to the rear outlet from the radio? That will tell you if the fault is with the head unit or the speaker system (wiring etc). Also, to further isolate the speaker wires, just run some cheap speaker wire from the (working) front speaker outputs to the speakers (or just one) themselves.

You don't need any special equipment.
posted by Brockles at 8:42 AM on April 4

To be clear, you don't need to cut any wires, just carefully connect stuff together at the plug. Don't touch the two wires for each speaker together, as that will blow amps up and the like, but it should be relatively easy to test this. Alternatively, an old speaker with a couple of wires hanging off it would do this test if you are nervous of poking around in the plug too much. Connect the radio up (out of the dash) and poke the wires into the back of the (connected) plug by hand. There is usually more separation of the terminals (in terms of plastic between them) for insulation in that manner.
posted by Brockles at 8:45 AM on April 4

How would I do this without cutting any wires? Is there a youtube video that details the process for me?

I know nothing about nothing, but I can't think of a way of swapping the wires without cutting them, stripping the coating, and twisting them together in their new configuration.
posted by Nonce at 8:52 AM on April 4

Simple: Remove the plug from the stereo, so the wires have no chance of juice going to them. Remove the rear speaker, and tape the two terminals together. Then use a multimeter to test for continuity at the plug that goes into the stereo (or at the wires that feed into that plug, if the plug is aftermarket wired into the old vehicle wiring harness.

This way you can test for continuity of the wires, which in my experience can be mashed, cut, abraded, whatever.
posted by notsnot at 8:56 AM on April 4

You sound adamant about not cutting any cables until you know what the problem is, but I can tell you from experience it will be ten times easier to diagnose the problem when you can quickly and easily connect/disconnect those lines.
posted by Civil_Disobedient at 9:47 AM on April 4

Doesnt the radio hav a quick connecT? So in order to do a above he would have to cut the wires. Or he can go to the local auto sound stoe and get a harness that will adapt the car end of the quick connect to a series of bare wires. Then he can test without cutting.
posted by Gungho at 9:54 AM on April 4

How would I do this without cutting any wires?

It sounds like you are a little out of your depth with this, but let's crash on, but please double check everything you do before poking anything around in there.

If you REALLY don't want to cut the wires, you can use two small jumper leads (small piece of wire, stripped at both ends. Speaker wire is of course ideal) and poke in the back of the front speaker connection in the plug and jump across to the rear speaker connection and see if it works. You'll probably have to connect both wires (it's unlikely they share a ground). Connecting the two speakers together at the plug, essentially. Be very, very aware of which plugs are which and connect like for like. Do not let two wires from the same speaker touch if they are powered up.

You sound adamant about not cutting any cables until you know what the problem is, but I can tell you from experience it will be ten times easier to diagnose the problem when you can quickly and easily connect/disconnect those lines.

This. Cutting and rejoining a wire is nothing at all to worry about. Really. Just make sure you mark them and/or sketch where they go before you start. Label accordingly if you have a few the same colour.

- Always cut wires a little distance from the plug - too close and you'll not be able to put any joiners in there and you'll be stuck. 2-3 inches away is an absolute minimum.

- Bullet connectors are cheap and reliable and easily switchable around while you are playing. Also easy to use are Chocolate block connectors (second one down).

- Strip about a half inch of wire at the end of each one you cut, and twist it tightly before you do anything with it at all. A twisted wire is much easier to deal with than one that has started fraying.

Then you can swap speakers out at the plug (car side or radio side, depending on where you have enough slack wire to insert the connectors) and see what is giving an output and what isn't. It's pretty simple to do.
posted by Brockles at 10:01 AM on April 4

So far, the simplest solution I have seen is this:

1. remove the wires from a rear speaker and ensure they are physically connected together.

2. obtain a wiring harness and slap it on the plug

3. test the appropriate two wires for continuity

Does that sound about right?
posted by Nonce at 11:06 AM on April 4

Yes, but that only proves if the wires are good - that's by far the least likely failure mode of your issue, though. It doesn't tell you if the speakers or the head unit are ok. My bet is the head unit's rear feed is down, and the best way of testing that is to wire the (working) front speakers to one of them.
posted by Brockles at 11:34 AM on April 4

For what it's worth, I spent several weekends tracing nearly every wire in my car to diagnose why I wasn't getting sound at the rear speakers. After eliminating every other possibility, which involved: removing the dash to trace the wires, removing the seats and floor mat to trace the wires further, it turned out to be the speakers themselves.

nthing recommendation to cut the wires and try a replacement. You can get a working junkyard radio from Pick-n-pull for as little as $10. The wires are a possible point of failure, but less likely than the radio and the speakers (which are moving mechanical devices that, depending on installation, are directly exposed to the sun).
posted by zippy at 11:48 AM on April 4

Oh, one more tip. If your speaker wires are thin enough (measure with a wire gauge), you can use these awesome solderless, no-mess telephone butt splices to put them back together. Ace Hardware sells them by the bag for cheap.
posted by zippy at 11:52 AM on April 4

Thanks for all the advice.
posted by Nonce at 11:48 PM on April 6

I replaced the factory speakers. Do they contain chemicals/elements/materials that shouldn't be thrown away? If so, how do I dispose of them properly?
posted by Nonce at 11:16 AM on April 9