Audio Systems: 93 Toyota OEM, power radios, factory speakers

Question
Hi Tom> As a former expert under an obscure category I offer congrats at your exemplary stats. I shall outline as clearly as space allows my present endeavour. Upon searching the web regarding car audio upgrades, my thoughts of what really made for better performance at minimal expense seemed substantiated. My plan is to keep the factory fm/cass head, which sounds quite satisfactory thru the door and rear speakers. Using the cassette adapted Walkman for CDs works for me, and remedies theft concerns.
As of today, I have accessed and removed the head unit and obtained both male and female harness connectors. Also ready to go are a 7 band 20-20k EQ with hi and lo inputs and 4 output circuits. The 1/2 DIN sixe fits well in the dash and powers up on initial test. A 10" JBL sub with box and 2 channel bridgeable amp with lo input only awaits connection. This brings up my questions for you: Is my scheme to use the four existing speaks thru the EQ and sub thru the new brided amp reasonable? If I have a cable raw at one end and matching the 13 pin 1/2" round DIN connector at the other, can this be utilized for a lo RCA output to feed the sub/amp? Is using the line level output to the EQ a problem? I have compiled all appropriate wire color and pin function data, and wire work shall happen only between the harness extending connectors and Din cable, I hope. I need some confidence to press on, and am open for real critical thoughts. Thanks awfully for your time. >Will  

Answer
Hello Will,
I have a couple of things to address, first you need to find the power output rating of the factory stereo. Second, the power rating of the factory speakers. As for connecting your factory stereo to the EQ, it depends on the make of the radio. On most radios that have high power outputs you cannot connect the speaker outputs to anything except directly to speakers, unless you have the proper speaker level to line output adapter. On high power radios if you measure the speaker outputs with the radio on , you will measure 5-6 volts DC on each speaker wire. If you do not use the proper adapter you can burn up the audio amps in the radio if any of the outputs are grounded. Back to your speakers and EQ, the output of the EQ is most likely line level output. If the output is line level then you will need an additional 4 channel amp for the existing factory speakers. Please give me the model of your car and the model number of the factory radio and I can tell you right off if this is a high powered radio and advise you further on steps to take to make your system work. If you need Tech Help in the future please feel free to contact me direct at: tdeser@zoominternet.net

TOM,
T&D ELECTRONICS