Connected a Dual XPA2100 300 watt amp to the battery and connected ground to chassis of vehicle. Vehicle is 2004 Saturn Ion with battery located in trunk area. Amp does not power on, all connections are tight; unsure if ground connection is considered viable connection. Also was provided a remote ground connection; also unsure if that was supposed to be connected from head unit. Vehicle/head unit power on, both fuses from battery cable to fuse located on amp are still good; but no lights or power going to amp

After you disconnect the battery, you have to reset the security system. The immobilizer is stopping the car from starting.

https://www.google.com/search?q=2004+saturn+ion+security+reset

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Here are some simple things that you can check and look for.

Check the voltage at the amplifier power input terminals. You should have 12 to 14 volts there with the vehicle running and the radio turned on. Check the voltage between the positive terminal and the chassis ground. It should be 12 to 14 volts as well. Check for a fuse at the POSITIVE batery terminal on the line feeding your amp. There should be a large amperage fuse there. Make sure that it is not blown. Check that the vehicle ground wire (from the chassis to the battery NEGATIVE terminal) is corrosion free at both ends and is connected tightly.

Also check that there is no corrosion or loose connections on these high power cables. At 2500 watts output from your amplifier, you should probably have #4 or #000 wire runing to the amplifier. These cables (one for the positive line and one for the negative) should run directly from the battery to the amplifier.

Good luck.

Most are located behind the starter

Check your ground wire. It should be solidly connected to the vehicle chassis in a a paint-free location. Also make sure the speaker leads aren't touching each other at the input on the amp. Then make sure your live power wire has a good connection to the battery and the amp. Finally, check the speaker leads along their entire length, and make sure they are not touching the vehicle chassis.

Check the ground wire. If you have a bad ground, you will not have any speaker output. The ground should be solidly connected to the vehicle chassis in a paint-free location. Check the live power wire as well, it should be connected directly to the battery. Then check the speaker leads to the amp. They should not be in contact with the vehicle chassis, or (at the input slots on the amp) with each other.

Check the power wire and the ground wire to the amp. The ground wire should be solidly connected to the vehicle chassis in a paint-free location. The live power wire should be directly connected to the battery. Also check the fuses, both on the amp itself and in-line with the live power wire (this fuse should be within 24 inches of the car battery). Those are the most likely culprits.

Make sure the fuses aren't blown. There should be fuses on the amp itself and an in-line fuse in the live power wire near the car battery. If the fuses aren't blown, make sure the remote wire is connected from the head unit. Then re-check your power and ground connections. The ground should be solidly connected to the vehicle chassis in a paint-free location.

Make sure you have a proper ground wire connection. The ground wire should be connected solidly to the vehicle chassis in a paint-free location. If it is loose or there is paint t the connection site, you will have problems with the amp output. Also check the speaker wires to see if they are touching the vehicle chassis. This will cause a short circuit and you will not have output from the amp. Finally, check the leads from the head unit. They should be RCA cables, and should have a good connection to the amp.

they are located under the hood. It looks like the battery, but it isn't. I leard the hard way when in needed a jump. the batter is in the trunk next to the tire. There is also one in the vehicle drivers side under the radiio behind the cover

Try to locate the cause of the discharge current as below:-

While vehicle electrical system shutdown as for overnight storage, connect an ammeter (with suitable current capacity and sensitivity) across the main ground connection between the battery -ve terminal and vehicle chassis/frame - (-ve of the ammeter to -ve battery terminal post, +ve to vehicle frame),
Carefully disconnect the main battery ground cable from the chassis,
The ammeter will now measure the battery discharge current - a discharge current in the order of 0.5 amp or more is of concern.
If all is well, the current draw should not exceed 50- 100 mA.
Note- Do not switch on any load while ammeter is connected, as ammeter damage or overload will occur.
If an excessive discharge current is observed, remove all fuses etc to eliminate / locate cause.