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• Connect the left and right speakers to the FL and FR (+) and (–) terminals

• Connect the subwoofer to the RL (+) and RR (–) terminals. (The rear-channel Bass Boost control makes the rear 

channels preferable for subwoofer connection. See Bass Boost, on page 10.)

NOTE: You can also run both pairs of left and right channels bridged for a high-power two-channel system.

See Connecting the Inputs, on page 7, for information about connecting the inputs for bridged operation.

The GTO-804EZ and GTO-504EZ amplifiers have multiple input connectors with a routing switch that increases 
flexibility, so you can use these amps in a variety of audio system configurations.

The GTO amplifier routing switch lets you determine which input connectors drive the amplifier’s various speaker 
outputs:

• F: The front and rear speaker outputs are both fed by the Front Input connectors.

• F&R: The front speaker outputs are fed by the Front Input connectors; the rear speaker outputs are fed by the 

Rear Input connectors.

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Use RCA audio cables to connect source units with preamp-level outputs to the amplifier; use the supplied bare wire-
to-RCA adapters to connect to source units that don’t have RCA output connectors.

Use a small Phillips screwdriver to loosen the adapter’s set screws and insert the speaker wires into the holes on the 
back of the adapter. Tighten the set screws to secure the wires. 

Always connect the (+) speaker wire to the (+) terminal on the adapter and the (–) speaker wire to the (–) terminal on 
the speaker.

IMPORTANT: Make sure the (+) and (–) bare wires do not touch each other. Touching wires can cause a short circuit 
that can damage the source unit or the amplifier.

When you’re finished, plug the adapter into the appropriate input connector on the amplifier. 

• For bridged operation: Connect to the left input of each bridged channel pair.

The Aux Out connectors are unfiltered pass-through output connections that let you connect multiple amplifiers to a 
single source unit, such as when you’re using separate amplifiers for front/rear speakers and a subwoofer. Connect 
the GTO-804EZ/GTO-504EZ’s Aux Out connectors to the subwoofer amplifier's input connectors.

The Aux Out connectors are fed by both the GTO-804EZ/GTO-504EZ’s front and rear inputs, so the subwoofer amp 
will receive an input signal regardless of how the source unit's fader control is set.

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When you’re using the amplifier’s rear channels to power a subwoofer, the Bass Boost control can provide up to 12dB 
of bass boost at 45Hz. Set this control according to your personal taste, but be careful not to set the control at a high 
enough level to cause audible distortion or bottoming of your subwoofer. CAUTION: Only use the Bass Boost control 
if you’ve configured the rear channels to power a subwoofer. Using the Bass Boost control with full-range speakers 
can damage the speakers.

The GTO amplifier Power/Protection LED’s color indicates the amplifier’s operational status:

• LED is orange: Normal operation (power is on)

• LED is off: Amplifier is in standby mode

• LED is red: Amplifier is in protect mode

If the amplifier is in the protect mode (the LED is red), see Troubleshooting, on page 11.

IMPORTANT: Disconnect the vehicle’s negative (–) battery terminal before beginning the installation.

If you have not already done so, remove the two end caps that cover the amplifier’s connectors as explained in 
Mounting the Amplifier, above. This will provide easier access to all of the amplifier’s connectors.

No remote turn-on connection is necessary because GTO amplifiers include signal-sensing turn-on, which will turn 
the amplifier on when it receives an audio signal at any of its input connectors. The amplifier will automatically turn off 
approximately five minutes after the input signal ceases. 

If your audio system’s source unit includes a remote turn-on wire and you would prefer to use it, the amplifier 
will sense that you’ve used a remote turn-on wire and that connection will override the signal-sensing turn-on. If 
necessary, you can defeat the signal-sensing turn-on circuit by moving the Auto Turn-On switch to the “Off” position.

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If your amplifier isn’t performing the way you think it should, check to see if the problem is covered in this section 
before calling your dealer or contacting JBL customer service.

No sound (the amplifier’s 
Power/ Protection LED is off):

•  Check that the amplifier’s +12V and GND connections have been properly 

made.

•  Check if the fuse on the +12V wire located near the battery is blown; if so, 

replace it with an identical fuse.

•  Check all amplifier fuses; if any are blown, replace them with identical fuses.

•  If you are using the amplifier’s REM connection for turn-on, check that the 

wire is properly connected to the audio system’s remote turn-on wire or to the 
vehicle’s ACC power terminal.

•  If you are using the amplifier’s Auto Turn-On circuit for turn-on, check that the 

amplifier’s Auto Turn-On switch (on the amplifier’s bottom panel) is set in the 
“On” position.

No sound (the amplifier’s 
Power/ Protection LED is 
orange):

•  Check that all amplifier input and speaker connections have been properly 

made.

•  Check that the amplifier’s Gain controls are not turned all the way down.

•  Check that the vehicle audio system’s source unit’s volume control is not 

turned all the way down.

No sound (the amplifier’s 
Power/ Protection LED is red):

•  Confirm that the vehicle’s electrical system is supplying between 9V and 16V 

DC to the amplifier. If the supply voltage is outside of this range, correct the 
condition before attempting to use the amplifier.

•  If the amplifier has overheated, wait until it has cooled down before attempting 

to use it again.

•  Disconnect all speakers from the amplifier and attempt to turn it on again: 

–  If the amplifier turns on (the Power/Protect LED is orange), there is a short 

circuit in one or more of the speaker wires. Correct all short circuits before 
reconnecting the speakers to the amplifier.

–  If the amplifier does not turn on (the Power/Protect LED is still red), contact 

your authorized JBL dealer for assistance.

Sound only comes from some of 
the speakers connected to the 
amplifier:

•  Check that the settings of the amplifier’s Input Routing switches match the 

input and speaker connections made to the amplifier.

•  Check that the vehicle audio system’s source unit’s balance and fader controls 

are set to their center (midpoint) positions.

Sound is too quiet, even with the 
vehicle audio system’s head unit 
volume turned all the way up:

•  Check the amplifier’s Input Level switch. If it is set to “Hi1,” turn the amplifier’s 

Gain controls all the way down and reset the Input Level switch to “Low.” Then 
perform the Set the Gain procedure, on page 9, again.

Sound in the front/rear speakers 
is distorted:

•  If the amplifier channels’ Input Level switch is set in the “Low” position, change 

the setting to “Hi1” and perform the Set the Gain procedure, on page 9, again 
for those channels.

•  Make sure amplifier’s Crossover Filter selector for the distorted channels is set 

to HP.

•  Set the distorted channels’ Crossover control to a higher setting.

•  Check that the distortion is not originating from the vehicle audio system’s 

source unit.

Sound in the subwoofer is 
distorted:

•  If the amplifier’s Input Level switch is set in the “Low” position, change the 

setting to “Hi1” and perform the Set the Gain procedure, on page 9, again for 
those channels.

•  While listening to bass-heavy music, turn the Bass Boost control all the way 

down, and then gradually increase it until the distortion begins to return. 
Reduce the Bass Boost control setting slightly to eliminate the distortion and 
leave it set there.

•  Check that the distortion is not originating from the vehicle audio system’s 

source unit.

The amplifier’s Gain LEDs 
constantly illuminate red while 
the amplifier is operating:

•  Set the amplifier’s Gain LEDs switch in the “Off” position.

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