if its a common ground?

how do i install the cd player then because when i install it with just the 4 pos. wires to each speaker it is soft but when you touch the front left ground to the chassis it comes in normal, but there is interference when the van is running. please help

you have to attach all the ground wires to chassis at the same point

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2 Memphis HPO 12s
1 Memphis 1000D
2 Memphis 8s
1 Memphis MC200
4 Memphis 3way 6 1/2s
1 Memphis MC3004
4 Memphis Tweeters
1 Memphis 3-way electronic crossover
2 Memphis 5 1/4
2 Memphis 4s

This isn't true,  most new HU will not play with a common ground setup.  They will go into protect mode.  You will have run (+) and (-) wires from the HU to each speaker. 

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Do it right the first time

I understand that, but i assumed he had a unit that had common grounds ......

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2 Memphis HPO 12s
1 Memphis 1000D
2 Memphis 8s
1 Memphis MC200
4 Memphis 3way 6 1/2s
1 Memphis MC3004
4 Memphis Tweeters
1 Memphis 3-way electronic crossover
2 Memphis 5 1/4
2 Memphis 4s

True! 

Sonix29, what type of HU is it and what type of van are you putting it in?

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Do it right the first time

its a kenwood kdc mpv 5025 and its a 1993 ford econoline conversion van. can i just hook it up normal and it will work?

Your van is wired with the common ground set up,  You will have to run wire to each speaker.

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Do it right the first time

some european vehicles you dont have to run new wires... bmw 7 series ...older... you would just run all pos. and then use 1 neg .. works like a charm... but GOOD OLD FORD .. your runnin' wire .. now ..you do olny have to run to 1 side of the van.. cause once 1 side .. ie . speaker is aftermarket ground you can use the fact. wire for the other side.. . it doesnt matter how you do it as long as every speaker has their own pos. and neg.

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dont be a pet monkey ..use your dmm

on some fords its not just a common ground, it is a chassis ground, so then you would have to run new wires to all of the speakers and and replace the speakers.  the chassis of the speaker grounds to the chassis of the car and only one wire goes to it. 

when i hook up all the pos. i get a little sound the i hook the front left neg to the ground, chassis, or neg wire and its works fine. but when you start the van there is interference when the rpms go up. i just recently hooked it up the normal way and it works fine except when you fade to the left you can still hear outta the right, and when you fade right you cannot hear outta left. is this going to cause any problems?

yes rewire all the speakers

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dont be a pet monkey ..use your dmm

it will destroy your radio, it sounds like you are not taking anyones advice here, just rewire them and be done with it..