Car Stereos: amplifiers, jeep grand cherokee, using a digital multimeter

Question
I read your answer about speakers and amplifiers in a 1995 Jeep Grand Cherokee witch is what i have. I installed a new radio after being told it was bad (never knew there was an amplifier)and still have no sound but i do have power. How could I check the ampilfier to see if it's working or just bypass it as you mentioned in your other reply. Thanks

Answer
Hi Sid,

If you're using an adapter harness to connect the new radio to the stock plugs, be sure the blue wire in the adapter harness is connected to the blue/white wire from your head unit.

You can find the amplifier under the rear seat.  You can test it using a digital multimeter.  The power wire at the amplifier is purple; the remote wire is gray with an orange stripe (or possibly dark green with a red stripe).  Both these wires should test at 12 volts when the radio is turned on.  If the violet wire doesn't have power, there may be a blown fuse in the vehicle's fuse box; if the gray/orange has no power, then the remote wire at the head unit may not be connected correctly.

You can use the AC voltage function on a multimeter to test for an audio signal.  If the amplifier has power, and there's AC voltage on the speaker wires coming from the head unit (while music is playing), but no voltage on the speaker output wires at the amp, then you can be pretty sure it's a bad amp.

Bypassing the amp involves connecting the speaker input wires from the head unit directly to the output wires running to the speakers.  If you can't get the system working, send me a follow-up and I'll try to get you the wire colors for the various speaker wires.

Hope this helps!

Brian