add_action( 'show_user_profile', 'dealer_auction_extra_user_profile_fields' );
add_action( 'edit_user_profile', 'dealer_auction_extra_user_profile_fields' );
add_action( 'personal_options_update', 'dealer_auction_save_extra_user_profile_fields' );
add_action( 'edit_user_profile_update', 'dealer_auction_save_extra_user_profile_fields' );

function dealer_auction_save_extra_user_profile_fields( $user_id )
 {
 if ( !current_user_can( 'edit_user', $user_id ) ) { return false; }
 update_user_meta( $user_id, 'dealer_registration_number', $_POST['dealer_registration_number'] );
 }

function dealer_auction_extra_user_profile_fields( $user )
 { ?>
 <h3>Extra Custom Meta Fields</h3>

 <table class="form-table">
 <tr>
 <th><label for="dealer_registration_number">Dealer Number</label></th>
 <td>
 <input type="text" id="dealer_registration_number" name="dealer_registration_number" size="20" value="<?php echo esc_attr( get_the_author_meta( 'dealer_registration_number', $user->ID )); ?>">
 </td>
 </tr>
 </table>

<?php }?>