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  • Installing Protective Lift Pump Relay

       (3 reviews)



    The life pump is powered through the ECM via pin #15 and #35.   Every time the lift pump is energized the power drawn through the ECM causes heat.  After a few thousands cycles of start/stops this heating up and cooling down cause’s degradation in the solder joints and failure.  Another possible cause of ECM failure is higher than normal amperage load by either a larger capacity lift pump or a failing pump.   As a lift pump starts to go bad (wear internally) the AMP load is increased to overcome the resistance.  This added power draw can cause the ECM circuit board to overheat and solder joints to open. The lift pump power routed through a relay protects the ECM from power spikes and excessive amperage loads.  The power load on the ECM is now less than 200mA.  The lift pump circuit is also protected by a dedicated fuse.


    1. WIRE: 4 colors if possible, size determined by load and distance, see chart.

    2. Fuse holder with fuse: AMP rating determined by load.

    3. Relay: Bosch type/mini ISO, terminal 87 normally open (NO) with suppressor, AMP rating determined by load. 

    4. 6 (or more) solderless insulated female spade connector, 6.35 mm (.25”) sized for wire gauge.

    5. 2 (or more) solderless insulated male spade connector, 6.35 mm (.25”) sized for wire gauge.

    6. 1 (or more) solderless insulated barrel connector, gauge size for fuse holder.

    7. 2 ring terminals, one sized for ground wire and the other sized for fuse holder connection.

    8. Dielectric grease, for terminal connections.

    9. Self-adhering  Velcro, for attaching relay to PDC.

    10.   ¼” protective wire cover or wrap cut to length.



    1. Wire cutter

    2. Wire stripper

    3. Crimping tool for solderless connectors,  a small pair of Vice-Grips will work.

    4. A 13mm and 10mm  socket or wrench.

    5. Volt, ohm, amp (VOA) meter with 20amp scale.

    6.  Optional, Soldering gun/iron with rosin core solder


    Locate the ground wire for the lift pump and place the VOA meter leads in series anywhere between a grounding point and the negative terminal/wire of the lift pump.  With the negative VOA lead connected to ground and the positive VOA lead on the negative side of the lift pump turn the meter select to the 20 amp DC scale, turn the ignition key to the on position and the lift pump will run for 5 seconds.  Read the amp draw and make note of it.  The fuse, relay and wire size will be based on it.  In this example we will use a hypothetical draw of 8.6 amps.


    Finding the correct fuse size is simply multiplying the load in amps times 135% (1.35).  In this example 8.6 amps multiplied by 1.35 equals 11.61 amps. The next sized fuse larger than 11.61 amps is 15 so for this example a 15 amp fuse will be used.


    Wire size is based on fuse size and length of wire.  The wire has to be able to carry a larger load and not burn up before the fuse does.  If the wire gauge is too small for a given distance then the resistance in the wire will cause a drop in voltage.  This reduced voltage reaching the lift pump will cause it to run slower and produce less pressure.  The voltage not reaching the lift pump is given off as heat. Using the wire gauge chart an 18 AWG is the minimum size used for this example.




    When an electric motor starts there can be a sharp volt/amp load placed momentarily on the relay contacts so the relay should be rated 2-3 time the motors normal amperage.  The motor in this example runs at 8.61 amps times’ 3 equals 25.8 amps so the next size relay that can be used is one rated at 30 amps.

    The relay of choice is the mini ISO otherwise known as the Bosch type in either 4 or 5 terminal, normally open (NO).   Relay terminal 30 is switched power or common in, 87 is switched power out and normally open circuit (NO) when no power is applied to the relay coil.  Terminal 86 is the positive or triggering terminal and 85 is the grounding terminal for the relay coil, check relay wire diagram for specific applications.  Terminal 87a is normally closed (NC) when no power is applied to the relay coil.  If you find a relay marked 20/30 this means terminal 87a is rated for 20 amps and terminal is rated for 30 amps.

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    Using a relay with a built in voltage suppressor is a must.  The relay will have a resistor or diode in parallel with the relay coil.  This suppressor reduces the back flowing voltage spikes to the ECM when the power to the relay is shut off and the magnetic field around the coil collapses.  Most relays denote the use of a suppressor with a symbol of a resistor or diode in the wiring diagram printed or etched into the relay cover.  Pay extra attention to the +,-  of pins #85 and 86 when installing a relay with a suppressing diode, if not installed properly the relay can be damaged.   Napa relay part #ECH AR272 is ratted for 30 amps and has a resistor suppressor.






    First disconnect the batteries.  Now  determine where to place the relay.  The relay can be placed on the PDC with Velcro, my Edge EZ has been mounted to the PDC this way for over 12 years.  This will keep the electric components in one area, a shorter wire run for relay terminal 30 and no holes in the metal where rust can start.  Do not put a screw through the PDC housing; there is the risk of wire or component damage.

    The source of the constant 12volt power can be either the positive terminal of the left battery or for a neater installation use the large cable stud in the PDC.   Install one end of the fuse holder using an appropriate sized ring terminal to the 12 volt terminal and with an insulated female spade connector attach the other end to relay terminal 30.


     If the wire for the fuse holder is to short connect extra length with either an insulated barrel connector or solder them together and insulate with heat shrink tubing.

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    Find the wire harness used for the lift pump, pulling back the protective wire wrap there will be a yellow wire with white tracer (yl/wt) and a factory connector.   This is the factory lift pump power supply and will be used as the ‘trigger’ to open and close the relay contacts.   The power source can be verified by attaching a test light or volt meter to it and turning the ignition key to the on position, there will be 12 volts for 5 seconds.  The yl/wt wire can be cut 2½”-3”from the factory connector. NOTE this is another place where an amp lode test could be performed.   Connect the new correct size wire with either male/female insulated spade connectors, insulated barrel connector or solder/heat shrink to the end coming from the ECM.  Attach the other end of the new wire to relay terminal 86 with an insulated female spade connector.   Consult relay diagram if diode protected. 

    Connect another new wire to relay terminal 87 with an insulated female spade connector and the other end of the wire to either the factory connector where the yl/wt wire was cut or to the lift pump itself.    


    The picture above shows new insulated spade connectors, the wire on the left is from the ECM to terminal 86 and the wire on the right is from terminal 87 to the lift pump.


    The relay grounding wire is attached to relay terminal 85 with an insulated female spade connector and the other end using a ring connector to the body.  The bolt that holds the PDC to the inner fender is a good spot.  Reconnect batteries and test.

    When routing wires take care that they are kept away from moving parts, ie: steering column,  have enough length so as not to pull loose and are covered with protective wire cover or wrap.  Use dielectric grease on connections to keep corrosion to a minimum or solder and seal with heat shrink tube.



    The relay and fuse can be installed in the PDC giving it the appearance of an OEM part.  Some of the connectors used in the PDC are not available in the general market but can be found in an auto/truck salvage yard.   I went to a ‘pick your part’ type salvage yard and found a 1999 Ram 1500 with V8.  The PDC is basically the same as my 2000 diesel.  You can either buy the whole PDC or remove the terminals with wires attached that will be needed. Leave as much wire as possible; the excess can be trimmed later.    


    Disconnect connect the battery, remove the PDC cover and locate where a spare fuse and relay can be added.  Remove the two sheet metal screws (10mm socket) and lift the PDC up.  The PDC housing can now be opened by gently lifting the plastic clips on the sides and prying it apart.  Now the bottom of the top half is exposed. Drill a hole large enough for three wires to pass through in the lower half of the case.  This is where the wires for relay terminals 85, 86 and 87 will exit the PDC.    The additional wire length is added by soldering and heat shrink tubing or insulated barrel connector to the used OEM connectors. These connections will be protected in the lower half of the PDC.  Pass the wires through the hole and place the salvaged connectors into their appropriate relay slots.  The other end of the wires can now be trimmed to length and connected as described in the installation instructions option a above.   Place the 2 halves of the PDC together and remount the PDC to the inner fender while grounding the relay terminal 85 wire with one of the screws, reconnect battery and test.


    My truck lift fuel pump amp draw is 6.5 amps so at 135% protection needed is 8.77 amps, next standard size fuse is 10 amps.   Relay size is 3 x 6.5 amps = 19.5 amps so a 20amp rated relay is needed.  I used a micro relay which is half the size of a mini relay because it can handle 20 amps and there were 4 empty positions I could put it in verses 1 position for a mini relay in the PDC.   I put the relay in a spot marked for an O₂ heater.   My truck has a Fuel Boss mechanical fuel pump and I have this electric pump as a backup so I run the engine with the 10amp fuse in the glove box. 

    With a fuel pump relay the fuel system can be primed without the ignition key being turned to the on position by jumping relay terminal 30 to 87.  As long as the two terminals are connected the fuel pump will run. 


    Written by:

    J. Daniel Martin, Martin’s Mobile Maintenance

    AKA: IBMobile



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       7 of 7 members found this review helpful 7 / 7 members

    Hi all.  New to forums and blogs, this is my first post ever.  I was compelled to review this post having completed it over the weekend.  First a great big thank you to IBMOBILE for putting it out there.  It helped me tremendously.  I opted for option "B" and added a micro relay with dedicated fuse inside my PDC.  I went to a self pull it salvage yard and removed the entire PDC from a 1500 series donor with all wires attached.  Cost $18 bucks and about an hour to locate and recover a suitable part.  Located the fuel pump relay inside the donor part and decided to use this one as it was the easiest to get to, and I figured a fuel pump relay was what I needed anyway, and it was the same one used in the how to photo, the one with a diode and ending in a "C" part number.  Side note: I tried like the dickens to figure or find anywhere on the internet and called reputable parts suppliers to determine the amp capacity of this and other relays, all for naught....nothing to be found. Just wanted to be thorough, and did not want a relay hanging on the outside.  Everyone wants to sell one for any given vehicle application, but they do not know anything about the part, or other possible applications.  That's why I used the relay and dedicated fuse spot in my PDC same as the photo.  I used the wires and relay from the donor PDC and used split plastic conduit to run my wires from / to my new FASS DDRP02 lift pump.  If you did not know this was a modification, you could not tell it from a factory input.  As a word of caution to anyone wanting to do this, I highly suggest purchasing the entire donor PDC.  The wires inside do not just slip out of their current position when you back probe to unlock them.  My donor had other locks in place to be removed, and even then I ended up destroying the relay and fuse positions just to salvage the wires intact.  I took my time to note and record the wire color and position prior to removal.  My "good truck", was a little easier to deal with, although I had to remember I was looking at my PDC from the bottom, and things were backwards looking from the top. If that makes sense.  I put it all together as stated in the tutorial, and I could not be happier.  I had done this mod because I had lost lift pump power from my ECM.  Referred from this forum, I had my ECM repaired and re-flashed at AutoComputerSpecialist in Florida because of lost lift pump power supply, and no Wait to start light.  Also, my truck had a race car cam lope at start up and then would die.  Doug at BlueChip Diesel helped me diagnose my problem and rule out the injector pump, as it would run smoothe when hot wired.  Thanks again to this forum for the lead, and thanks to Doug at BlueChip.  He will return your call and help you.  Unheard of these days.  Also a big shout to AutoComputerSpecialist.  They happened to have a sale going on for repair jobs, and already repaired ECM's.  I gave them a call thinking I was going to purchase a new to me ECM.  The super nice and knowledgeable lady talked me into a repair rather than a purchase.  Again, unheard of these days.  I am so glad I listened to her.  She saved me about $300 bucks, and the repair along with the communication via email was astounding.  My truck is now up and running better than ever.  I also did the ground wire mod and the alternator charge wire mod, as AutoComputerSpecialist told me that my problem originated from low voltage cranking, even though my cranking speed was up to par.  Thanks again to this forum for all the help. 

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       1 of 1 member found this review helpful 1 / 1 member

    My truck is an '02 and I am the original owner.  Back around 2005, warranty covered VP44 replacement and a retro-fitted in-tank lift pump.  At this time the dealer relayed the lift pump using the control signal from the ECM, so I do not have to make this modification. 


    Hats off to you for recognizing that the factory should have never wired the lift pump directly from the ECM in the first place.  Great detail in showing how to make the conversion!


    - John

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       1 of 1 member found this review helpful 1 / 1 member

    I just did this mod after I installed my FASS 165. I was noticing hard starts as mentioned in other threads that ultimately got me on to this mod. I went with the basic install on the side of the PDC with some velcro. I re-purposed the relay cover that FASS provided with the pump and slid the new relay inside that, it made for a very clean install. The only hiccup I ran into was reading too far into the diagram that shows the 15/35 pin wires joining into one. I had to do some digging on the internet before I realized that that step had already been done coming out of the ECM and the result is the yellow/white wire that is described in the instructions (exactly as shown in the wiring diagram haha). Anyway, great instructions, thanks for all the good info on this website.

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