How to Wire an Amp to a Sub and Head Unit

A sub woofer or two in a vehicle can make the world of difference in listening to music. It is very important to match the RMS of your subs to your amp. You want an amp more powerful than your sub, because you don't want your sub to clip. Clipping is the number one reason of bass.


  1. Image titled Wire an Amp to a Sub and Head Unit Step 1
    Gather your equipment (Amp, Subs, Stereo, and wiring). You can find wiring kits at most stores, ~$40 for 4 gauge wiring and In-line fuse, you won't need anything larger than 4 gauge.
    • If you're using an after market head unit, go to an electronics store's stereo department and ask for a wiring harness from your car to the after market head unit. Example : If you have a Chevy and a Sony stereo go to them and tell them you need a Chevy to Sony wiring harness, they will ask you the year of the vehicle and then go pick it off the shelf, these are usually by the install department behind the counter. once you have it go unscrew your stock stereo, unplug it, plug in your new wiring harness, and plug in the other end to your Stereo. When you buy the new wiring harness make sure its the same shape/size as your stereo.
  2. Image titled Wire an Amp to a Sub and Head Unit Step 2
    Run your amp wires (battery, ground). Figure out where you're going to place the amp, put the beginning of your power (red) wire there and give it about a foot of wire extra, then begin to hide and run the power wire to under the hood. Some vehicles may have existing holes filled with a plastic/rubber insert. Run the power wire through the firewall. If you need to drill a hole in the fire wall, be careful not to hit anything on the other side and be sure the drilled hole will not cut through your power line. Electrical tape at the entry point will give the wire added protection. Make sure this wire is safe from any moving objects.
  3. Image titled Wire an Amp to a Sub and Head Unit Step 3
    Detach the power cable from the battery and attach your amp's power wire to the power cable for your vehicle; leave it unattached. If you bought a kit it comes with an inline fuse, if you didn't, you need to get an inline fuse. Just cut the power wire, insert the inline fuse and reattach. The fuse amperage should match the gauge size.
  4. Image titled Wire an Amp to a Sub and Head Unit Step 4
    Place the amp where you want it, then attach the ground (black or brown) wire to the amp. Ground it to a piece of bare metal (not painted); most people unscrew a bolt from a seat attach the wire and screw it on. Lightly sand the contact area to expose clean metal before attaching ground.
  5. Image titled Wire an Amp to a Sub and Head Unit Step 5
    Now for the RCA jacks, If your using a after market stereo on the back there is 2 RCA jacks, just run the RCA from there to the "IN" on your amp and try to avoid running RCA jacks alongside power lines to minimize noise.
  6. Image titled Wire an Amp to a Sub and Head Unit Step 6
    If you're going to use your stock stereo and run the amp from there you want to buy a Line Out Converter ~$20. With the converter you get a small box with 2 RCA's coming out and 4 speaker wires out the other. You want to take out a door speaker and run 2 of the 4 speaker wires to it, pay attention to the positive (+) and negative (-) terminals. You don't need the other 2 speaker wires, from here secure the Line Out Connector out of sight and run the RCA's to the amp, plug them into the "IN" RCA jacks.
  7. Image titled Wire an Amp to a Sub and Head Unit Step 7
    Now for the Remote (blue wire). If you're using After market Stereo there will be a blue wire coming from the wire harness in the back, mostly these are attached so you have to splice, just snip them and tape off the old end and run your remote wire to your amp. If you're using your stock head unit you have to purchase a toggle switch that fits your fancy, find a cool place to mount or hide it, from here you want to attach the remote wire to your amp, run it to your toggle, cut it, attach it to one terminal, then attach the end you just cut to another one. Then run the remote wire back to the amp and cut it there leaving a foot or so of extra cable. This will come into play later.
  8. Image titled Wire an Amp to a Sub and Head Unit Step 8
    Use a capacitor to prevent voltage drops caused by deep bass hits, i.e., lights dimming with the beat. Get your capacitor as close to the amp as possible, and use the same ground as you did for the amp. Have your power wire taunt and find out where your cap. is going to be, cut the wire, and attach the battery cable to the battery. You cannot just plug it in; you must charge it first with a resistor, use a 1k ohm resistor because they do not get as hot, it only takes a few seconds to charge, do not do this bare handed. You want to ground your cap. and grab a voltmeter and place them on the cap. take the resistor and place it in the power side of the cap. and attach the power wire to the other end of the resistor, your voltmeter should jump up to around 12.0 Volts, then your cap. is charged.
  9. Image titled Wire an Amp to a Sub and Head Unit Step 9
    Run the power wire to your amp. If you have a stock stereo and you have the remote wire there you want to in twine the remote wire with the power wire before inserting in the power slot for amp. The remote wire tells the amp to turn on. so if you don't have the remote wire from the after market head unit to turn on the amp when ever you turn on the stereo you have to turn your amp on manually. Make sure you always turn off your amp when you leave your car, it will overheat and drain your battery.
  10. Image titled Wire an Amp to a Sub and Head Unit Step 10
    Run your sub wires to the amp and screw them in.
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    Turn the gain all the way down, start playing music and turn it up to where you usually listen, where the mids sound good. Tune them gain until the subs sound good.
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    RMS is very important when matching subs and amps, yes not enough power will make subs clip, but also to much power will burn your voice coils by over heating them with too much power . Subs and amps should be matched as closely as possible for best performance and longevity.


  • Don't forget to test your rem wire before you assume it works. Last thing you need is a dead battery.
  • If your amp doesn't turn on, check the amp fuses.
  • When connecting a line out connector to a factory head unit, it is advisable to use both sets of speaker wires to maintain the left and right stereo effect from modern music.
  • Soldering 12v power and ground connectors to the wires will reduce circuit resistance and make your power cleaner, giving you better sound.
  • Always remember to shut off the amp if you do so manually
  • Make sure that you use cables with the correct resistance (or impedance) for your setup. A bridged amp runs at a different impedance than the same amp in unabridged mode. Getting this wrong may well overheat cables or even blow the amp itself so make sure your cables and setup are matched. Common values are 2, 4, or 8 ohms, so do your homework beforehand.


  • Always Disconnect the Negative terminal from your battery before doing anything with electricity on your car.
  • Always be careful with electricity.

Things You'll Need

  • Stereo
  • Amp
  • Subs
  • Wiring kit
  • Screwdriver and/or hex set
  • Socket set

Article Info

Categories: Cabling and Wiring Connection