This article is written for 99+ Super Duties.  The procedure would be the same for the 94-97 trucks, only the mounting location would be different.

Time Required

Items needed:

• Marinco onboard charger outlet - about $16 from your local boating supply store (or BoatersWorld.com for you landlubbers)
• Silicon seal
• Zip ties

Tools needed:

• Drill with 1 7/8" hole saw (or smaller bit and sanding drum, saber saw, etc)
• Knife
• Pencil
• Channel locks
• Multi-meter (optional)

Installation:

1. Locate the stock plug behind the drivers-side tow hook.
2. The plug's cord runs through a plastic sheath that is taped to two plastic hangers on the back of the bumper and zip-tied to itself.  Remove the tape and the zip tie.  This part isn't easy but persistence pays off.
3. Locate a spot to mount the outlet on the plastic trim below the bumper near the driver's side wheel.  (see photo below)  Be sure there is no metal or other interferences behind.  While there are other places to mount the outlet (there's about 2' of extra cord), I picked this one to avoid cutting through metal or chrome and so it's easy to see if the cord is still plugged in when getting in the truck.  Some other ideas for mounting the plug (which will require more tools and material):
   • Behind a custom front license plate
   • Outboard of the tow hooks
   • In the rear bumper
4. Drill the hole.
5. Hold the plug with the ground terminal up and cut off the stock plug.  Note which wire is on which side to ensure the correct polarity on the new outlet.
6. Remove the threaded locking ring and rear boot from the outlet.
7. Pass the cord through these items.
8. Run the cord through the new hole in the bumper.
9. Separate and strip the wire according to the outlet's directions.
10. Install the wires into the outlet and tighten the terminals.
11. Insert the outlet in the hole.  Be sure to orient the ground terminal up.
12. Tighten the locking ring with the channel locks and slide on the rear boot.
13. Seal around both sides of the waterproof boot with the silicon seal.
14. Fasten the extra cord with the zip ties.
15. Grab a cold one and admire your work.

Finished Block Heater Plug Mod

It blends well with the stock bumper color

A note about extension cords:

Let's look at a 100' 14 gauge cord:
Current = 1000 W / 120 V = 8.4 Amps
Voltage drop = 8.4 amps * 0.258 = 2.2 volts
% voltage drop = 2.2 V / 120 V = 1.8% voltage drop = OK

Gauge	Resistance/100' @ 77°F
#12 wire	0.162
#14 wire	0.258
#16 wire	0.409

Other ideas: