Car Stereos: Constant Power for s-10 1996 stero, harness branch, cigarette lighter

Question
I recently bought a truck for the winter, as 1996 S-10.  The original harness was cut (ground, constant, and ignition switch power) were wired into the new hardness for the aftermarket deck.  The speaker wire (only) two were left intact, however the speakers above the dash were wired in using a high gage speaker wire, bypassing the speakers.  This wiring had the speakers sharing the ground wire which doesn't make sense.

So my questions are:

Do I need to ground the speakers? If so, why/how?

If the constant power doesn't work (I tested the voltage meter) what should I tie into?  I tried to tie into the interior dome light switch which was a mistake as it kept all the lights on.  What other sources are recommend (e.g. cigarette lighter, etc.)?  I wanted to ensure I don't blow a fuse.

Otherwise, if the constant doesn’t work, and I the wire is intact with the other wire (within bundle for original factory harness)  how could I fix?
Thanks.

Answer
Hi John,

Yes, you need to independently ground the speakers.  If this means having to run fresh wire back to the deck, then do that.  Your sound quality will thank you immensely.

As for where to get power, it sounds like there's something else messed up in there, as tying into your dome lights should not have made them come on all the time.

You need to ground out the black wire from the aftermarket harness to a clean chassis point.

Connect the 12V (red) wire to a wire that has power when the car is on, but has zero volts when the car is off.

Connect the 12V (yellow) wire to a wire that has power all the time.

Which wires provide which functionality changes from car to car, but I usually poke around with a multimeter to find what I want.  Any wire circuit will usually do.

If you wanted to go all out, you'd run a fresh wire off of the positive battery terminal (fused, of course), and then run it to the yellow in the back of the harness, branch off of it, and run it into the input on a relay, using the switched circuit you find as a relay switch, preventing you from drawing any extra electricity from any other circuits (well, except the minute amount needed to fire a relay), and preventing confusion.  That, unfortunately, is a lot of work.

Justin