Mine was all off yours being an 8-track, including the link. Pop the cover and check the could solder joints. From what I've read on this many over time separated.
2nd...many of these have a schematic stamped into the stop cover.
Take a look at this one on ebay. I couldn't pull the image out but one pic shows the stamp in the front center on the top cover.
http://www.ebay.com/itm/78-84-Delco-...6e5584&vxp=mtr
Finally, this may help.
http://www.the12volt.com/installbay/...etail/564.html