Factory Radio Wiring

Here is a better look at the inside of the speaker ground plug. And a schematic for the radio.
View attachment 1715288232 View attachment 1715288233

Sorry to hijack this thread. My 71 has the same connections and I just picked up a radio that's supposed to "light up and made noise when tested". Anyway, my test light shows power on the J4 Dual light connector but I can't get anything out of the J3 A lead.

Should I get test light power on both those leads?