Can You Wire in Multiple Amps, or Are Are You Limited to Just One?

How to Wire Multiple Amps in a Car

wiring two or more ams
Most people will get by fine with one, but check out any truly premium or competition car audio system and you'll see they have wired two or more amps. mixmike / E+ / Getty

Wiring in one amplifier can be complicated enough, especially when you're dealing with a factory car stereo, and the situation just gets more complex when you add multiple amplifiers to the equation. You can wire two amplifiers, or even multiple amps, in one car audio system, but it takes some extra planning.

The main factors that you need to consider when you wire in two or more amps are how you will deal with the power cable, grounding each amp, and whether or not the remote turn-on signal from your head unit is strong enough to split between multiple amps.

Can You Have Multiple Amps in One Car Audio System?

The short answer is that you can use any number or combination of power amps in a car audio setup as long as you wire them in properly. The main proviso is that the charging system has to be able to provide enough juice in the first place. If you add in too many amps, and they draw too much power, you may need to upgrade your alternator or install a stiffening cap.

As to whether it’s better to use one multi-channel amp or multiple amps to power your various speakers, that depends on factors like the amount of available space, the results that you’re looking for, the amplifier classes you use, and personal preference.

The most common reason to wire in multiple amps is to have one for your main speakers and a second amplifier for a subwoofer.

If you do decide to go with multiple amps, the process of multi-amp wiring is similar to single amp setups. You have a couple of options, but it’s important to take the increased current draw into account in any case.

Multiple Amp Wiring

Regardless of the number of power amps you use in your car audio system, it’s important that you stick to wiring best practices.

In terms of amp wiring, that means getting your power straight from the battery. With that in mind, you have the option to either run separate power cables for each amp, or a single cable that feeds all of them. Depending on your particular setup, either one of these options may work out for the best.

In most cases, a single power cable is the most elegant solution. If you decide to go with that option, then it’s a good idea to use the thickest gauge power cable that will work in your application.

Due to the fact that your power cable needs to handle the current draw from all of your amps at once, it needs to be significantly larger in gauge than called for by the specs of your individual amps. For instance, if 8 gauge cable is sufficient for your amps, you may want to use 4 gauge cable for your run to the battery.

The best way to wire multiple amps to a single power cable is to use a power distribution block. That allows you to use a single cable for most of the run, including the crucial portion that passes through the firewall, and then to use shorter individual cables to actually connect to each amplifier. A distribution block can also be fused, which is helpful if your amps don’t include built-in fuses.

Amp Ground Wiring

Rather than grounding your amps individually, a distribution block should also be used to provide the ground connection.

In a mirror image of the power distribution block, the individual amps should be connected to the ground distribution block, which in turn should be connected to a good chassis ground. You can use the same ground block for your other audio components, which is also a good way to avoid ground loop issues.

Multiple Amp Remote Turn-On Wiring

In some cases, you may find that a single remote turn-on lead is unable to handle the current draw demanded by multiple amps. One way to work around this issue is to connect the turn-on leads from your amps to a relay, which is triggered by your head unit.

Wiring suggestion for two amps with a relay for the remote turn-on.

Rather than receiving power from the head unit, the relay should be hooked up to another source of battery voltage—either from the fuse box or directly from the battery. That will effectively isolate the turn-on signal from the head unit from the multiple amps, which will hopefully allow you to avoid any issues with current overload.

Amp Wiring: Head Unit and Speakers

The way that you wire your head unit to your amp will depend on the outputs on your head unit. If your head unit has multiple preamp outputs, then you can connect each set of outputs directly to one of your amps.

If your head unit doesn't have multiple preamp outputs, then you’ll have to check your amps. In some cases, internal amp wiring includes preamp pass-through functionality, which allows you to connect multiple amps together. In that case, you can connect the pass-through outputs on your first amp to the preamp inputs on your second amplifier, and so on.

If your head unit doesn’t have multiple preamp outputs, and your amps don’t have pass-through functionality, you’ll need to use Y adapters to split the signal between your amps.

The amp wiring situation can be a little more complicated if your head unit doesn’t have any preamp outputs at all. In that case, you’ll use speaker wire to connect your head unit to your amps, and you’ll either need power amps with speaker-level inputs or a line output converter to provide you with line-level inputs for your amps.