Manual for Pioneer DEH-P3500MP says - "Sound from this unit is muted automatically when a call is made or recived using a connected cellular telephone". How to connect cellular telephone to this unit ????????????

i shouldn't think so.

parts.pioneer.com this is a link to the dealer / part you are looking for the price is about 112.50 USD you may find a cheaper one with a little more research.

This is directly from the installation manual from pioneer website for model DEH-P6600

(Yellow/black
If you use a cellular telephone, connect it via the
Audio Mute lead on the cellular telephone. If not,
keep the Audio Mute lead free of any connections.)

Basically, you don't hook it up unles you have a cellular telephone in your vehicle, not a personal cell phone.

on some pioneers you have to turn the deck off and push the function switch for a few seconds. then you should be able to scroll through the menu to find clock adjust.

HERE is your manual in PDF format.

This unit doesnt have a volume mute function.

What are the problems you are experiencing.

If it says Mute or ATT on the display - it is the cellular mute function turning off the volume for an incoming call.

Page 34 details turning on and off the cellular mute function.

You also may try a hard reset by removing the face, and pressing the reset button.

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I am having the exact same problem with my vauxhall corsa and my pioneer deh-6000ub its so annoying it works with the manufacture stereo soon as i connect my pioneer in it doesn't come alive (the HCB-400)

see pg 26 of the manual:
http://www.pioneerelectronics.com/pio/pe/vgn/images/portal/cit_11221/50145operation_manual_DEH-P3500_20021241432238500.pdf

Yellow/black
If you use a cellular telephone, connect it via the
Audio Mute lead on the cellular telephone. If not,
keep the Audio Mute lead free of any connections.

Orange/white
To lighting switch terminal.

Blue/white
To system control terminal of the power amp or
Auto-antenna relay control terminal (max. 300
mA 12 V DC).

The yellow/black wire at the back of the head unit may be grounded. Make sure it's not pinched or shorting on anything.