Over the years, your old Direct Drive OEM Starter has probably been very reliable. These starters utilize a large field coil to create a magnetic field which moves the drive gear into contact with the flywheel. But eventually you probably have found several performance issues that may have caused undo aggravation.
First off, these are bulky starters that weigh approximately 20 pounds in OEM form. Their large size can create clearance problems around headers and are prone to radiant heat soak that can cause intermittent operation. Additionally the Direct Drive Starters demand a large amount of current which can drain your battery after only a few crank attempts. You may also have found that they do not work as well with high compression performance engines due to the lack of torque output from the drive gear.
In the 1990s, Ford started to use the PMGR (Permanent Magnet Gear Reduction) Mini-Starter. This new design uses a starter mounted heavy duty solenoid and a planetary gear train which allows the armature to rotate at greater speed with increased torque. The PMGR has no field coil and instead uses high performance ceramic-ferrite magnets.
These were found to have many advantages, such as 40% more torque through 4.5:1 gear reduction, much smaller in size providing more clearance and weigh only half as much as the old Direct Drive Starter. By eliminating the field coil and providing an efficent gear reduction, the PMGR requires much less current and substantially reduces drain on your battery.
Selecting the correct Ford PMGR part number is important as the automatic and manual starters are not interchangeable. On the automatic PMGR Starter, the drive gear has a longer nose and the drive gear extends 3/8" further in order to mate with the recessed flywheel ring gear. If the shorter throw manual PMGR Starter is installed in an automatic, it will not engage with the flywheel and simply spin.
Wiring your PMGR Starter is fairly simple and slightly different from your old Direct Drive Starter.
***Move the Main Starter Motor Wire from the "M" switched side of the Starter Relay to the "B" Battery Side of the Starter Relay, so the Starter Motor has constant 12v battery power. The other end of the 4 gauge wire connects to the open large post on the Starter Solenoid.
There may be a second large external post on the PMGR Solenoid with a thick wire that connects power directly to the Starter Motor. When starting, the two large Solenoid posts will interconnect internally allowing full power to the Starter Motor.
***If you run out of room on the Starter Relay "B" Post, install a Power Distribution Stud for all of your accessory wires.
Easy and inexpensive, you probably should have one of these anyway. Simply install the Stud, run your Battery+ to the post and then jumper to the Battery side of the Starter Relay. The Starter Relay "B" post should only have the Battery, Starter Motor and Alternator cables attached.
***Then run a separate smaller 12 gauge wire from the "M" switched side of the Starter Relay to the small "S" Start Post on the PMGR Mounted Solenoid.
You may have to enlarge the 12 gauge wire terminal to make it fit over the larger "M" post unless you fabricate the wire with the correct terminals. Your Ignition Key will then activate the Starter Relay which in turn will send 12v to the Starter Solenoid. When you release the Ignition Key the Starter Relay will open immediately halting power to the Starter Solenoid and will disengage the Starter Motor from the Flywheel. When properly wired, there will be no electrical connection between the Solenoid Start post and the always hot Solenoid Motor post.
Your new PMGR Starter may come with a Bus Bar to facilitate using the original Direct Drive Starter wiring by connecting the relay switched Starter Motor power to the new Starter Mounted Solenoid. DO NOT USE THE BUS BAR or jumper the large Starter Solenoid Main Post to the small Solenoid Start Post in an attempt to eliminate the need for a separate 12v Start Wire.
Doing so can damage your PMGR Starter by causing Starter Run-On for approximately 2 seconds after you release the start key. This is due to the remaining spinning starter motor energy generating mechanical voltage until it has completely stopped.
A motor uses electrical energy to produce mechanical energy, and a generator uses mechanical energy to produce electrical energy. They are very similar. If a motor is spun it will produce electricity.
When the Starter Relay opens, there is no BATTERY power going to the starter, but the voltage generated by the spinning starter motor can keep the new PMGR Starter Mounted Solenoid from de-energizing quickly and retract the gear from the flywheel.
Ford specifically warns:
"! ! ! WARNING: DO NOT INSTALL A JUMPER WIRE BETWEEN THE BATTERY TERMINAL AND THE SOLENOID BLADE TERMINAL AT THE STARTER TO AVOID THE USE OF THE # 12 WIRE. IF DONE, VOLTAGE IS GENERATED TO THE SOLENOID BY THE STARTER SPINNING AFTER THE RELEASE OF THE START KEY OR BUTTON, CAUSING THE STARTER TO REMAIN ENGAGED, RESULTING IN SEVERE DAMAGE AND EVENTUAL FAILURE OF THE STARTER ! ! !"
Remove the Bus Bar or jumper and rewire correctly by using a 12v Solenoid Start Wire... :twak