I have a pioneer car stereo model DEH-P3900MP and i need to know how to change the time on the clock...

SOURCE: pioneer

turn the HU off...hold down the source button for a couple of seconds and the screen will pop up with the time on it...easy to change from there with the "left, right, up, down" buttons surrounding the source button.

SOURCE: i don't know how to change the time on the clock

With the power OFF, press and hold the FUNC button until date and time are displayed, use the UP/DN/RT/LT toggle to change values and positions, once time and date are set, turn unit ON.

I’m happy to assist further over the phone at https://www.6ya.com/expert/robert_aad3edb7dfa380b9

Instant Repair Help over the Phone

6ya.com

Save Time & Money by instantly connecting to...

SOURCE: how can i change the hour on the clock of my

Try this:
How do I set the clock on my single CD player? For most Pioneer single CD players, you can set the clock using the following steps:

1. Press and hold the SOURCE button until the unit shuts off.
2. Press and hold SOURCE again until the clock appears. With some models you will press and hold the FUNCTION or AUDIO button instead of the SOURCE button.
3. Press the left or right arrow to select the segment of time you wish to adjust.
4. Press the up or down arrows to increase or decrease the numbers in the blinking segment.
5. Once the clock is set correctly, press the SOURCE button to exit.

SOURCE: wiring diagram for pioneer deh-p3900mp?

Page 2 of 6 covers wiring diagram for DEH-P3900MP.
http://www.pioneerelectronics.com/pio/pe/images/portal/cit_11221/370942420DEHP3900MPInstallationManual1027.pdf

SOURCE: need wiring diagram for pioneer deh p3900mp

here is the link to your manuals:
http://www.pioneerelectronics.com/PUSA/Support/CarAudioVideo/In-Dash/CD-Players/ci.DEH-P3900MP.Support
see pg 2 of other manual for wiring diagram

Cheers!