Vintage booster/ equalizer

I found a bit of Sparkomatic nostalgia for myself and I've noticed that the input from the stereo has only positive lugs, no negatives. Would I connect all left negative wires to the desired left negative output posts and all right negatives to the desired right negative posts?

The old booster I had had the same layout, but had one negative post under the two positive left and right input posts.

Can anyone help or am I barking up the wrong forum?

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Author: Deano