Stereo Harness help

[big66440]

Hey guys I tried installing a new head unit on my Comanche last night and could not get it to work, I checked the voltage at the harness( the one that plugs into the head unit itself) and at the radio fuse and it's at 11.89 volts on both  with the engine off/ ignition switch on ACC. I also did a voltage drop from the positive battery terminal to the same locations and came up with .31 voltage drop which seems a bit too much , I was wondering if there was an easy quick way to clean up a connection or some of the connections to get more juice to my head unit so it can work ( i tested the head unit directly to the battery and it works) or if you guys had suggestions on properly bypassing the factory harness and adding a circuit so I can finally listen to some music while driving, thanks in advance :D

[relyt120]

I would upgrade the dash ground as a first step see Cruiser54's renix tips

[Co-MAAAN-cheee]

I have a 88. I recently replaced the bulb sockets for the turn signals. After I noticed that when my flashers are on the back light on  the stereo led dims in unison. then a couple of days ago I was using the tape deck while charging my phone from the lighter and the radio fuse (it was 15amp) burned out. I did all of cruzers electrical stuff last year except for the connector block under the air box. C101 elimination, new ground under dash, everything.  When I replaced the bulb sockets I cleaned the connector under the air box. Honestly I'm not certain the dimming wasn't happening before I worked on the lights. I'd sure appreciate some advice on what to check. I'm no pro, but, I have a multi meter and know how to solder. I'm tempted to run a ground just for the radio and put the lighter on its own fuse. Ideas?