I've got a 1998 Grand Cherokee with the 5.9 V8. It has the factory Infinty Gold speakers and amplifier. How do I hook a subwoofer up to that amp? Any suggestions or a link to a guide would be great because I've already sunk $75 into a sub.

 

What sub did you purchase? Is it a sub with a built-in amp? What I did was get an older Bazooka Tube with a built in amplifier which taps into the outputs from the headunit. Simple installation, and nice sound. I remember also seeing Kenwood releasing a newer flat panel amp+sub unit that you can attach to the back of the rear seats. But iirc that'll cost you several hundred bucks.

Just adding a sub speaker to the Infinity amp is not going to work well. You'll need a crossover/filter that passes 80-120Hz frequencies, and below. Also the Infinity amp doesn't have enough power to drive a sub.

 

The amp itself will have + and - places to connect the + and - to your speakers. The amp simply needs to have power to it and the turn on wire that runs from the stereo. Some higher end amps may use the red and white audio connectors built into the wires themselves.

 

You can't hook a sub to that amp unless it has an extra channel or 2 to do so, and I doubt it does.

You need a separate amp, I suggest a monoblock instead of bridging a 2 channel. (more efficient)

Have you bought your sub yet? I suggest buying a 4 ohm instead of 2 ohm, (less work for the sub)

Make sure your sub RMS matches your amp RMS for best set up. (150 RMS sub and amp for example)

Make sure you buy the proper sized enclosure for the sub, the instructions in the sub box will tell you the proper box size.

Have you decided on an sealed box or ported?

Sealed to save space, and for tight punchy bass, ported for SPL (LOUDNESS!)