JBL Grounds???

[rbg15]

I have a '95 eb. with the JBL "premium" audio. My head unit won't power on. When I went to test the wires, I read the there are two grounds (blk + grn/blk). The green and black ground seems to be good, but not getting any continuity out of the plain black one. I'm testing this using the "hot when acc or run" yellow/blk. I have no idea about fixing grounds at all. Here is the wiring diagram I've been looking at. Any ideas would be greatly appreciated!!

 

[dezufo]

I presume you are checking between the wires using a meter set on 12v
If you had 12v between y/bk and bk/lg then you know you have power coming from fuse 11 and that the bk/lg is well grounded
You need to check that you have power from fuse 1 as well
You should be checking with the main connector removed from the radio unit and make sure the ends of the leads are touching the metal bits inside the connector

If you get 0v on the blk wire then you know that there is a break in it, less than 12v the wire has a bad connection where it connects to the bodywork.

Going on your diagram that blk wire has a splice connection S200 and a connector C212 before it is bolted to the bodywork at G204. I can not tell where they are because my manuals are different to yours.

If the blk wire has a break or bad connection then you can cut it as far from the main connector as possible then terminate the wire with a ring crimp connector and bolt/screw it to the bodywork
If it does not have a break or bad connection then the problem is inside the radio unit.