12V Battery Lead issues

I have a 91 Chevy Lumina that my father installed a crap tapedeck into some years ago. A friend of mine just got a new HU so he gave me his Alpine. I got this wiring diagram for chevy/gm vehicles and hooked the HU up accordingly. The HU won't power on. So I did a little troubleshooting and I have come to find out that the indash wire that is supposed to be the 12v battery lead isn't hot. I tested it with a 12v tester. Everything else is ok, I know becase the 12v ignition lead works, so i hooked BOTH the HU's Battery and Igniton Leads to the same indash igniton lead and the radio powers up. The only problem is that without the battery lead giving constant power to the HU, when I turn the ignition off, the HU loses all settings and radio presets. If the other tapedeck worked without any problems I think I am just missing something. I also wonder if I can just run my own 12v Lead straight from the battery. Is that possible and what guage should I use if possible? Please help, Thanks   iLLz

Have you by any chance checked the fuses?Certified Security Specialist

Always check info with a digital multimeter.

I promise to be good.

Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.

yea shortly after posting this, that is exactly what i did and that was the problem. thankfully it was a simple solution. thanks for the reply, if i hadn't checked them and fixed it, you would have pointed me in the right direction. the12volt.com rocks iLLz