diff -u b/core/modules/file/migration_templates/d7_file_private.yml b/core/modules/file/migration_templates/d7_file_private.yml
--- b/core/modules/file/migration_templates/d7_file_private.yml
+++ b/core/modules/file/migration_templates/d7_file_private.yml
@@ -6,27 +6,27 @@
   plugin: d7_file
   scheme: private
   constants:
-    # source_file_private_path must be set by the tool configuring this migration.
+    # source_full_path must be set by the tool configuring this migration.
     # It represents the fully qualified path relative to which uris in the files
     # table are specified, and must end with a /. See source_full_path
     # configuration in this migration's process pipeline as an example.
-    source_file_private_path: ''
+    source_full_path: ''
 process:
   # If you are using this file to build a custom migration consider removing
   # the fid field to allow incremental migrations.
   fid: fid
   filename: filename
-  source_file_private_full_path:
+  source_full_path:
     -
       plugin: concat
       delimiter: /
       source:
-        - constants/source_file_private_path
+        - constants/source_full_path
         - filepath
   uri:
     plugin: file_copy
     source:
-      - '@source_file_private_full_path'
+      - '@source_full_path'
       - uri
   filemime: filemime
   # filesize is dynamically computed when file entities are saved, so there is
reverted:
--- b/core/modules/file/src/Plugin/migrate/source/d7/File.php
+++ a/core/modules/file/src/Plugin/migrate/source/d7/File.php
@@ -83,12 +83,8 @@
     $path = str_replace(['public:/', 'private:/', 'temporary:/'], [$this->publicPath, $this->privatePath, $this->temporaryPath], $row->getSourceProperty('uri'));
     // At this point, $path could be an absolute path or a relative path,
     // depending on how the scheme's variable was set. So we need to shear out
+    // the source_base_path in order to make them all relative.
+    $path = str_replace($this->configuration['constants']['source_base_path'], NULL, $path);
-    if (isset($this->configuration['constants']['source_file_private_path'])) {
-      $path = str_replace($this->configuration['constants']['source_file_private_path'], NULL, realpath($path));
-    }
-    else {
-      $path = str_replace($this->configuration['constants']['source_base_path'], NULL, $path);
-    }
     $row->setSourceProperty('filepath', $path);
     return parent::prepareRow($row);
   }
diff -u b/core/modules/file/tests/src/Kernel/Migrate/d7/MigratePrivateFileTest.php b/core/modules/file/tests/src/Kernel/Migrate/d7/MigratePrivateFileTest.php
--- b/core/modules/file/tests/src/Kernel/Migrate/d7/MigratePrivateFileTest.php
+++ b/core/modules/file/tests/src/Kernel/Migrate/d7/MigratePrivateFileTest.php
@@ -35,7 +35,7 @@
     // Set the source plugin's source_file_private_path configuration value,
     // which would normally be set by the user running the migration.
     $source = $migration->getSourceConfiguration();
-    $source['constants']['source_file_private_path'] = $fs->realpath('private://');
+    $source['constants']['source_base_path'] = $fs->realpath('private://');
     $migration->set('source', $source);
     $this->executeMigration($migration);
   }
diff -u b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
--- b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
+++ b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
@@ -104,8 +104,10 @@
     // @todo Find a way to avoid this in https://www.drupal.org/node/2804611.
     if ($definition['destination']['plugin'] === 'entity:file') {
       // Make sure we have a single trailing slash.
+      if ($definition['source']['plugin'] === 'd7_file_private') {
+        $configuration['source']['constants']['source_base_path'] = rtrim($config['source_private_file_path'], '/') . '/';
+      }
       $configuration['source']['constants']['source_base_path'] = rtrim($config['source_base_path'], '/') . '/';
-      $configuration['source']['constants']['source_private_file_path'] = rtrim($config['source_private_file_path'], '/') . '/';
     }
 
     /** @var \Drupal\migrate\Plugin\Migration $migration */
diff -u b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
--- b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
@@ -1049,8 +1049,6 @@
 
         // Store the retrieved migration IDs in form storage.
         $form_state->set('migrations', $migration_array);
-        $form_state->set('version', $form_state->getValue('version'));
-        $form_state->set('d6_source_base_path', $form_state->getValue('d6_source_base_path'));
         $form_state->set('source_base_path', $form_state->getValue('source_base_path'));
         $form_state->set('source_private_file_path', $form_state->getValue('source_private_file_path'));
 
@@ -1200,13 +1198,7 @@
     $storage = $form_state->getStorage();
 
     $migrations = $storage['migrations'];
-    if ($storage['version'] == '6') {
-      $config['source_base_path'] = $storage['d6_source_base_path'];
-    }
-    else {
-      $config['source_base_path'] = $storage['source_base_path'];
-    }
-    $config['source_private_file_path'] = $storage['source_private_file_path'];
+    $config['source_base_path'] = $storage['source_base_path'];
     $batch = [
       'title' => $this->t('Running upgrade'),
       'progress_message' => '',
diff -u b/core/modules/migrate_drupal_ui/src/Tests/MigrateUpgradeTestBase.php b/core/modules/migrate_drupal_ui/src/Tests/MigrateUpgradeTestBase.php
--- b/core/modules/migrate_drupal_ui/src/Tests/MigrateUpgradeTestBase.php
+++ b/core/modules/migrate_drupal_ui/src/Tests/MigrateUpgradeTestBase.php
@@ -127,16 +127,11 @@
     $drivers = drupal_get_database_types();
     $form = $drivers[$driver]->getFormOptions($connection_options);
     $connection_options = array_intersect_key($connection_options, $form + $form['advanced_options']);
-    $version = $this->getSourceDrupalVersion();
     $edit = [
       $driver => $connection_options,
       'source_base_path' => $this->getSourceBasePath(),
-      'source_private_file_path' => $this->getSourcePrivateFilePath(),
-      'version' => $version,
+      'source_private_file_path' => $this->getSourceBasePath(),
     ];
-    if ($version == 6) {
-      $edit['d6_source_base_path'] = $this->getSourceBasePath();
-    }
     if (count($drivers) !== 1) {
       $edit['driver'] = $driver;
     }
@@ -203,22 +198,6 @@
   abstract protected function getSourceBasePath();
 
   /**
-   * Gets the source base path for the concrete test.
-   *
-   * @return string
-   *   The source base path.
-   */
-  abstract protected function getSourcePrivateFilePath();
-
-  /**
-   * Gets the source base path for the concrete test.
-   *
-   * @return string
-   *   The source base path.
-   */
-  abstract protected function getSourceDrupalVersion();
-
-  /**
    * Gets the expected number of entities per entity type after migration.
    *
    * @return int[]
reverted:
--- b/core/modules/migrate_drupal_ui/src/Tests/d6/MigrateUpgrade6Test.php
+++ a/core/modules/migrate_drupal_ui/src/Tests/d6/MigrateUpgrade6Test.php
@@ -32,20 +32,6 @@
   /**
    * {@inheritdoc}
    */
-  protected function getSourcePrivateFilePath() {
-    return '';
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function getSourceDrupalVersion() {
-    return 6;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   protected function getEntityCounts() {
     return [
       'aggregator_item' => 1,
diff -u b/core/modules/migrate_drupal_ui/src/Tests/d7/MigrateUpgrade7Test.php b/core/modules/migrate_drupal_ui/src/Tests/d7/MigrateUpgrade7Test.php
--- b/core/modules/migrate_drupal_ui/src/Tests/d7/MigrateUpgrade7Test.php
+++ b/core/modules/migrate_drupal_ui/src/Tests/d7/MigrateUpgrade7Test.php
@@ -33,19 +33,6 @@
   protected function getSourceBasePath() {
     return __DIR__ . '/files';
   }
-  /**
-   * {@inheritdoc}
-   */
-  protected function getSourcePrivateFilePath() {
-    return '';
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function getSourceDrupalVersion() {
-    return 7;
-  }
 
   /**
    * {@inheritdoc}
@@ -65,7 +52,7 @@
       'editor' => 2,
       'field_config' => 53,
       'field_storage_config' => 40,
-      'file' => 3,
+      'file' => 2,
       'filter_format' => 7,
       'image_style' => 6,
       'language_content_settings' => 2,