Audio Systems: Car audio signal, radio sahck, amp settings

Question
Is there a way to check and see if I have a signal being output from the RCA jacks (subwoofer output).  What equipment do I need?  I installed an amp & sub, checked all connections and settings.  The power light comes on the amp, but no sound.  I also checked to make sure the headunit subwoofer setting is on.  Thanks for any help. Kevin.

Answer
Right, first question, a cheap multi-meter from Walmart or radio Sahck is needed for most tests on a car so good idea to buy one, less than $10 is O.K.

Now! You installed an amp and a sub. RCA from sub out to amp. 12v from battery plus via a fuse to the plus on amp, heavy earth to body and the blue signal wire to switch on the amp from the radio. Two speakers wires from + & - output to sub + & - . Amp power on lamp comes on but nothing on sub. Right?
Things I would check first,
Have you 12vdc at the main battery cable on the amp?
Settings on the amp, have you set the input dial to about 75%?
If you have bridged the 4 speaker output to two for a sub have you set the amp to "bridged"?
Using a multi-meter set for 20DCV check for a small voltage on the RCA inner to outer and see if it increases if you turn up the volume, Yes, readio is ok, No? radio is duff or setup are wrong, re-read the manual and double check everything, sometime if all else fails reading the intructions solves it.