Two ground wires to Stock Radio?

I am replacing the factory radio in a 95 explorer with a Kenwood Radio/CD player.
The replacement radio supplied harness has one ground wire, which is black.
The factory radio has two harnesses going into it from the vehicle. One which carries the power/illumination wires etc. and includes a ground wire (black). The other harness carries the speaker wires. The connector for the speaker wires has 9 wires in it, 8 for the speakers and a black ground wire.
When wiring an aftermarket wiring harness, which also carries a ground on each connector is it correct to connect both of these grounds together and connect them as a pair to the radio ground wire on the radio supplied harness?
I wasn't expecting to see two grounds going into the factory radio and wondered why Ford used two grounds to the same device. The Chiltons manual I have does not include a diagram for the radio and speaker circuits so I am at loss to explain this.
Car does NOT have JBL sound. The aftermarket harness with the correct connectors claims to be for Premium sound systems, tho' I wasn't aware that the factory radio was anything other than standard, it doesn't claim to be premium on the face plate or ID stickers when you remove it.
Any advice is welcome.
JP
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One of the grounds is the illumination ground. You don't want to use that for a aftermarket radio unless it has incandescent light bulbs inside of it and a separate ground feed for these bulbs (trust me it doesn't).
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