2000 Ford Superduty
Diesel Engine Disabler Circuit

SuperDutys are too easy to "disappear" without the owner's knowledge, so I built this device to slow down the bad guys.  It won't keep the determined ne'r-do-well from getting my rig (nothing will), but it will keep the joyriders from having a good time with mine.

The concept is to interrupt the power to the IDM (Injector Drive Module) relay in the under-hood fuse/relay box.  This is the relay that supplies power to the box that makes the voltage that fires the injectors.  Without voltage to the IDM, the engine won't start or run.  I used the IDM circuit instead of the PCM (Powertrain Control Module) relay, as I wanted my instrument panel to appear normal while the truck is being "violated", so as not to start the bad guys looking deeper into this.  Everything will appear as it should, it will even crank the starter motor.  The truck will just not start and run.

I use a dual-coil latching relay that interrupts the coil voltage to the IDM relay.  It's a Magnecraft 785XBXCD-12D.


UPDATE OCT, 2017: This Magnecraft relay is no longer available. Before using these instructions, BE SURE to locate one of these in the aftermarket or surplus, as all the instructions are based on using this relay, and will be completely incorrect if using a different part. All bets are OFF!

If you wish to re-design this system using a different magnetic latching relay, be my guest! A suitable substitute might be an OMRON MK2KP-UA-DC12 and this will require a different socket, as well.


This system was designed to take advantage of a feature to the vehicle's Remote Keyless Entry (RKE) system, but a provision can be made to still use this in a vehicle without RKE.

A feature of the RKE system is what happens when you push the remote's Lock button a second time.  The park lamps all flash and the horn very quickly "beeps".  The Park Lamp Relay is what's used to flash the lamps, and I use the voltage from this relay to power the disable (or "set") coil.  This allows me to not disable the truck each time I remotely lock it, but just when I confirm the lock with a second push of the remote button.

The other coil to enable (or "reset"), goes to a glass-encapsulated magnetic "reed" switch that is hidden behind a plastic piece of the truck's interior. 

I get into the truck, pass the magnet over "the spot", and the truck will then start like always.

The relay has two sets of contacts.  One is to interrupt the IDM relay coil, the other is used to power a self-flashing LED in the instrument panel as a reminder that the truck is disabled.  I know I have successfully found "the spot", and enabled it to start, when the LED stops flashing.

It's convenient, too, because I don't HAVE to disable it every time I shut the engine off, or even when I remotely lock it, and therefore don't have to subsequently re-enable it each time, either.  Just when I want to.

If you're interested in doing this kind of thing, and don't have RKE, you can put a small, momentary-contact switch somewhere convenient that will take the place of the signal from the Park Lamp Relay.  Hitting the button will disable the truck, and you'll have to know that there is a spot that needs to be "touched".  You could glue a magnet to something attached to your key ring.  You could get pretty creative with that.

Remember that this all applies only to a 2000 diesel-equipped Superduty, and you may have to modify things for use with a gasoline engine or another model year.

If you'd like to duplicate it, I gotta' tell you this isn't a one-afternoon project, but can easily be broken down into a few projects that get tied together at the end.

If you want to add this to your truck, here's how.

Click on them to enlarge most photos.

Parts Needed

The dual-coil latching relay can be ordered from Allied Electronics and is their stock number (now discontinued, see note above).  The socket for it, which isn't absolutely necessary but makes it a lot easier to mount and wire up, is Allied stock number 70185513 ($3.91).

Most other parts can be ordered from All Electronics. Other parts needed are:

Two small neodymium magnets, All Electronics #MAG-74 (2/$1.00)
    Two magnets are required for EACH remote "clicker"
    you will use, so you may need more than just two.
    (See note below about not using these)

Two one-amp power diodes, All Electronics #1N4005 (8/$1.00)

One six-amp power diode, All Electronics #D620 (2/$0.90)

Self-flashing red LED, All Electronics #LED4 (2/$0.90)

A magnetic reed switch is also needed, and can be found on eBay by searching for
"reed switch N/O"

A small fist-full of appropriate crimp splices, some shrink-sleeving, solder, etc.

UPDATE SEP, 2019: I am reminded that I no longer use my fobs to trigger my reed switch, and use a four inch long neodymimum bar magnet. Thus, the magnets inside the fobs are not really necessary. You can skip the next four sections if mot putting magnets into clickers.

Position the Magnets

The two magnets should be stuck together as shown, end-to-end.  They will only go together in this orientation in one way, and you can't get it wrong if you stick their ends together.

click to enlarge

Modify the Clicker, Type -AA

The following applies to Ford clicker part number F8DB-15K601-AA only.  Type -AB's are covered separately, below.  Remove the split-ring from the clicker.  Insert a small screwdriver between the two "tabs" and gently pry apart the two halves of the clicker to reveal what you see in the photo to the left.  The magnets mount in the cover, below the battery.  Make sure they clear the small metal "box" in the other half when re-assembled.  Glue them in place with a good grade epoxy.  Let the epoxy fully cure before re-assembling the clicker.

click to enlarge

Modify the Clicker, Type -AB

The following applies to Ford clicker part number F8DB-15K601-AB only.  Type -AB's have a larger battery that is mounted in a socket as part of the circuit board. Remove the split-ring from the clicker.  Insert a small screwdriver between the two "tabs" and gently pry apart the two halves of the clicker to reveal what you see in the photo to the left. The magnets mount in the plastic cover in the upper, right-hand corner as shown.  Glue them in place with a good grade epoxy.  Let the epoxy fully cure before re-assembling the clicker.  Note that this orients the magnetic "gauss" 90 degrees from that in the -AA's above.  Take this into consideration when passing your fobs over the reed if you have both types of fobs.  I prefer the -AA's myself, but I have one -AB that I use, too.







click to enlarge









Aligning the Magnetic Reed Switch
to the Fob's Magnets

You need to align the reed switch so that it will be the most affected by the magnets in the clicker.  If the reed is 90 degrees out of alignment, passing the magnets by it may not even affect it, so we need to understand what we're going to do next.

For this step, you will need a non-stick surface.  I have a collection of teflon sheets, so I used one 1/8" thick.  You could use something like teflon tape, or even a 2" x 2" flat piece cut from old plastic milk jug material.  Just first make sure that epoxy can't permanently stick to it.

Put the clicker underneath the plastic non-stick, back-side up, and roll the reed switch over the top of the sheeting until the reed "gets caught" by the magnetism.  Push the reed around and you'll see that it returns to the same orientation in respect to the clicker.  This is the relationship between the reed and the magnets in the clicker that is most effective, and you need to "index" the reed to preserve it.  You'll be creating a "flat spot" on one side of the reed by using epoxy.  Look at the photos.

Mix up some epoxy glue.  I used JB-Weld.  Lay a bead along each side of the reed, without disturbing it's magnetic orientation, and allow it to cure.  You should allow your clicker to remain in place for at least an hour, but the reed should cure for about a day.

After the epoxy is fully cured, use a razor blade to remove it from the non-stick sheeting.  Now you know why I used real Teflon.

When you have created your index flat, and the epoxy is cured, again place the flat surface you've created against the back side of your clicker and let the magnetism position the reed accordingly.  Determine where you will mount the reed, and how you will be passing the clicker over it.  You now know exactly the orientation the reed should be mounted behind something.  At this point, mark which end is toward the driver's side of the truck (or forward if that is the orientation). 


Mounting the Magnetic Reed Switch

Solder wires to the reed's leads that are long enough to make it back to the relay with some spare.  Cover all exposed leads with shrink-sleeving.   We don't want a short! One wire goes to ground, the other to pin 5 of the relay.

Determine where you will mount your reed switch.  It must not be on a metal surface, but that's OK, as most of our interior panels are thin plastic.  Find a place that's natural to pass your clicker over while getting into the truck.  This location should be known only to you, and I won't show where mine is located for this reason.  This could be as far away as in your headliner, behind the instrument panel, in the overhead console, in the door's side panel, wherever.  Use your imagination, but remember you need to run wires from it back to your instrument panel somewhere, and it can't be behind a metal surface.

Find the IDM Relay

On a 2000 Powerstroke, the relay box is under the hood, just outboard of the brake system master cylinder.  Pop off the lid and find the relay pictured here.  This is the IDM relay. We need to locate a WH/BK (white with a black stripe) wire on the under-side of this relay.










Find the Wire to Interrupt

Now comes the fun part.  We need to find a wire underneath this relay, so we will have to take the fuse box loose to turn it over.  The safest way to do this is to first disconnect the negative battery terminals at both batteries.  At this point you may want to get some additional space for this job by removing the air bax assembly. The easiest way to access the bottom of the fuse box is to start in the front.  Pry up the plastic cover that protects the main (heavy guage) power input wire, and set it aside.  Remove the nut (it will be very tight) that holds this wire's terminal to the fuse box.  Pry the two little clips on each side of the box that hold it to the support bracket, and lift up.  Three more clips hold the bottom cover onto the box.  Remove the bottom and gently turn the box at least 90 degrees so the underside faces you and you see what is in the photo at the left. A white with a black tracer supplies the ground from the PCM to the IDM relay.  In the photo, there is a tape "arrow" to point out the correct wire. In the wire bundle leading out the back of this fuse box you will find the "customer access" wires.  I used the red and black ones, but you can use any two available.  Cut the black-white wire and splice one end of the cut to the red customer access wire, the other end of the cut to the black customer access wire.  Tape over the wire bundle and put everything back together.  Try to start the engine.  It SHOULD NOT start, as the IDM power relay should not "make".  Pull down the access cover to the under-dash area below the steering wheel, and find the other ends of the customer access wires.  Refer to the photo at the left.  Now would be a good time to strip back the insulation to the red and black wires, twist them together, and try to start the engine.  This time it should fire right up.  If so, the under-hood wiring is OK.  Un-twist them and extend each of them to the area of the relay, using sufficient additional wire.

Finding the "Set" Input

If you do NOT have Remote Keyless Entry (RKE), any normally-off push-button switch can provide the momentary voltage to "set" the magnetic relay. Wire one contact of the switch to an "always hot" +12 volt source, and the other will be the "set" positive voltage input to the magnetic relay on pin B.

If you DO have RKE, locate the Park Lamp Flash relay, shown in the photo to the left.  It's in a covered relay box that's directly behind the radio, on the firewall, and will best be reached by removing the upper and lower instrument panels. There are two nuts that allow the box to pull down. The flash relay is the small one at one end (the other three are large, and are the Lock/Unlock relays). Pull the #26 fuse in the under-hood fuse/relay box.  Take off the two nuts that retain the assembly to the firewall, and pull down the assembly as far as practical.  Find the dark brown wire that goes to the back of that relay socket.  Do not confuse it with the "tan" wire, as it also looks brown but is much lighter. Cut the dark brown wire and insert the heavy-current diode in-line, with the band of the diode farthest away from the relay socket.  Splice a new brown wire onto the wire that goes to the socket, attaching it before the diode.  The other end of the new brown wire goes to the magnetic relay, and is our "set" positive voltage input. When you push your RKE clicker Lock button twice, a pulse of +12 volts will come down that brown wire. Replace the #26 fuse. Carefully route that wire to the area in which you'll mount the relay, being careful to avoid anything that moves under the instrument panel (brake pedal, steering shaft, etc).

Mounting the LED

I found that the best place to mount the flashing LED is in the instrument panel, itself.  There is a unused place for a light that reads "THEFT" in Excursions with the anti-theft system (same instrument panel), so naturally, that's what I used. That affords the best visibility to determine if the engine can start.  It also allows the "bad guys" to see there's SOME kind of "alarm" installed.  It's also probably the most difficult to do "right", as the panel has to come out of the vehicle to accomplish this.

The nice part is that there's already a constant +12 volts on half of this hole's socket, and an LED current-limiting resistor on the circuit board on the low side. Thus, providing a ground to the other side of the resistor will light the LED and produce the word THEFT in red on the panel.  Using a self-flashing LED will give you a flashing annunciation.

For you electronics buffs, I actually used a 555 timer, set to sink the LED's current for a third of a second, every three seconds, enabling me to use a super-bright red LED here. I have a slower rate than the self-flash LED I called for, but it's more difficult for those that have little electronics background to build, so I didn't go into details. For those of you that wish to do it this way, pick up the positive supply for the 555 circuit from the LED's supply, and just float the ground, taking it back to the relay. When the relay contacts allow the ground, you've got a flasher!











Wiring the Latching Relay

Determine where you want to mount the latching relay.  Put it in a location that's difficult to access.  I mounted mine above the GEM module, and simply tie-wrapped the socket to a nearby thick harness.  The GEM is accessable if you remove the instrument bezel panel. 

The inputs to the relay's socket are as follows:

Pin #    Wire from:
  1          User access wire from WH/BK  on IDM relay (under-
              hood fuse box)
  2          n/c (no connection)
  3          n/c
  4          n/c
  5          To one of the reed switch wires.
  6          Ground (and to the other reed switch wire)
  7          The other user access wire back to the WH/BK  wire on
              IDM relay (under-hood fuse box)
  8          Constant +12 volts
  9          Wire to "THEFT" LED in instrument panel.
  A          Ground
  B          Brown wire from diode added above, +12 volts "set".

In addition, "counter-EMF" 1N4005 diodes should be added across each of the relay coils to prevent premature switch contact erosion as follows:
Banded end on pin #8, other on pin #5
Banded end on pin #B, other on pin #A


If you have Remote Keyless Entry, click your remote's Lock button twice.  Does the horn "beep"? Do the park lights flash?

If you do not have RKE, push your "disabler button".

If you're wired correctly, you should have "set" the relay, opening the power to the IDM relay coil, and the red LED should begin to flash.  Click the Unlock button, and try to start the engine.  It should not start, but should crank over. The LED should continue to flash.

Remove your keys from the ignition and pass the clicker (or other magnet) over your "spot" in the pre-determined orientation.  The red LED should stop flashing.  If so, try to again start the engine.  This time it should start normally.


You can build a custom vehicle disabler that isn't like an alarm system.  Most joyriders know how to get around the common alarms, and will take your truck anyway! This one isn't "in the books", and will cause a "no start" condition for very different reasons than alarms do. Maybe it will only slow the professionals down a bit, but they aren't going to take the time to troubleshoot the no-start condition. At least you can do something to delay them, and they may just move on to another truck whose owner doesn't care as much as you do.

Does It Work?

I have had feedback from numerous people all over the country that have told me they have built this project.  One person has built it for all THREE of his SuperDutys!

NOTHING was more rewarding than the email I got in March, 2013 that said:

"Your disabler saved my truck!

"I had written you a while back asking you about how many guys had done your disable mod. Well, let me tell you it worked for me this past weekend here in [redacted].

"Thief (professional) broke cleanly door cylinder, then snapped off ignition and tried starting... it looked like he had some time, he disconnected interior light hoping it had something to do with the no-start. Thankfully he left without taking anything out of the truck.

"If I hadn't done the mod, and instead installed an over the counter alarm he probably would have figured it out and stolen the truck.

"Again thanks. Your idea saved my truck."

SpringerPop's F350 Page


write: SpringerPop

Last updated 03/20/18