Non-Buick - Which is pos and neg?

[84GNTTYPE]

I'm putting new speakers in the rear of my 91 Grand Am. On the left side there are yellow and a brown w/white stripe wires and on the right side there is a light blue and a dark blue wire both w/white stripe.

Any help identifying which is positive and which is negative would be appreciated.

Thanks

 

[zam70]

In ALL GMs, in the rear, the darker wire is positive (in front, dark is negative)