Good job with the battery... if the speaker "blips" then you have the correct + and - for that speaker. The speaker shouldn't make any noise if you dont have the right ground.

You might not have traced the wires far enough back if you don't have "8" wires. Basically you should have four "colored" wires and four black wires... you need to cut the grounds apart that are connected together. Follow the wires towards the radio opening. IIRC There are a set of the connectors like the ones that plugged into the back of the radio where the rear speakers connect to the wires that plug into the fader switch. you can get rid of the connectors and now you will probably see what I'm talking about.

If you still aren't quite sure take a picture and post it of the wires you're talking about. You shouldn't need any extra wire for the speakers. Just one wire for constant power. You can splice into the emergency flasher wire that has constant power and just run a short wire (maybe 2') up to the radio and then you will be golden. I found this idea on the forum so I wont take credit but it's a good place to splice because you don't have to run a long wire up into the dash.

-David

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'98 E300 Turbo "Juliette"
'85 Federal 300TD