Diesel Tailgate

Est 2003
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  § The Freight Train § F-Tempo § block heater mod § $10/$15 AIC

Marinco block heater plug mod

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This is my first article posted on TheDieselstop.com
This quick and cheap modification makes easier to plug and unplug your diesel for those cold mornings. This modification allows for 1 handed connection/disconnect in a better location. It's really waterproof, so it won't get corroded.

This article is written for 99+ Superduties. The procedure would be the same for the 94-97 trucks. Only the mounting location would be different. block heater

Time required

About 30-60 minutes

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)


  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 2 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's 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 that 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 lisense 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. Seperate 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

finished product
It blends well with the stock bumper color

A note about extension cords:

The block heater draws 1000 Watts. It should measure about 15 Ohms when tested with a multi-meter. The cord should see less than a 2% voltage drop to be safe:

Let's look at 100' 14 guage 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

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

Other ideas:

It's more pricey, but add an Auto-ejector plug instead.

Comments, suggestions, or questions about this site? Email Rob at email me.

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