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Old 05-10-2021, 08:26 AM   #1
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8.3 ISC lift pump wiring harness

I am in the process of installing a FASS pump, should have that portion done today.

I will then turn my attention to bypassing the OEM lift pump, have the fittings on order and will receive shortly.

I need to add the relay to "fool" the ECM and would rather not cut the wires but instead buy a wiring harness to plug the lift pump wires into and mount the relay in a dry location. Does anyone know the part number for the mating wiring harness???


Thanks in advance
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Old 05-10-2021, 10:09 AM   #2
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The ISC ( CAPS ) lift pump had a short duty cycle after key on , as opposed to the ISB that ran continually after engine start up .

If you plan on running the FASS continually with the engine running , then controlling the relay from the Cummins ECM won't work.
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Old 05-10-2021, 11:28 AM   #3
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It worked for me it fools the ecm into believing the lift pump on running for the 2 minutes until the ecm turns it off. The fass runs all the time. I made my own plug so I don't have a part number
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Old 05-11-2021, 07:07 AM   #4
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Originally Posted by jacwjames View Post
I am in the process of installing a FASS pump, should have that portion done today.

I will then turn my attention to bypassing the OEM lift pump, have the fittings on order and will receive shortly.

I need to add the relay to "fool" the ECM and would rather not cut the wires but instead buy a wiring harness to plug the lift pump wires into and mount the relay in a dry location. Does anyone know the part number for the mating wiring harness???


Thanks in advance
If I am not mistaken James the plug that plugs into the OEM lift pump is just a single connector with two male spades. I just ran two wires from that OEM connector to my battery storage and then hooked it up to a regular 12V 30A relay. That's all you really need to do. You are WAY over thinking this. You do not need a special connector or harness. I can't remember exactly what mine was but I know for a FACT I did not have to order or go out and buy anything or make up something special. Hardest part I remember was getting the wiring to the battery storage but that was not even difficult. Before you go out and buy anything just unplug the OEM lift pump and look at what kind of connector it is.
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Old 05-11-2021, 07:13 AM   #5
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If I am not mistaken James the plug that plugs into the OEM lift pump is just a single connector with two male spades. I just ran two wires from that OEM connector to my battery storage and then hooked it up to a regular 12V 30A relay. That's all you really need to do. You are WAY over thinking this. You do not need a special connector or harness. I can't remember exactly what mine was but I know for a FACT I did not have to order or go out and buy anything or make up something special. Hardest part I remember was getting the wiring to the battery storage but that was not even difficult. Before you go out and buy anything just unplug the OEM lift pump and look at what kind of connector it is.

You are probably right but I was just seeing if there was a female adapter to make it a cleaner connection. I will be crawling under the rig today/tomorrow to check it out. I have some spare relays that I carry, just have to make sure I have spad connectors that fit.
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Old 05-12-2021, 07:49 AM   #6
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You are probably right but I was just seeing if there was a female adapter to make it a cleaner connection. I will be crawling under the rig today/tomorrow to check it out. I have some spare relays that I carry, just have to make sure I have spad connectors that fit.
I'm pretty sure two regular spade fittings will work. No one will ever see the connection anyways. Once you plug it in just wrap with some black electrical tape so it will not come apart and you are set.
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Old 05-12-2021, 07:58 AM   #7
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I am actually going to extend the wires into my rear run bay and mount the relay there. I crawled up the rig again yesterday and Cummins must have been trying to save money as the pigtail to the lift pump is very short, no good place to get the relay out of the elements so I'll just add wire and put in the bay next to the rest of the ECM fuse holders. I'm going to take the original wiring male portion of the harness, cap the wires and plug it back into the fuel pump to protect the female portion.
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Old 05-13-2021, 06:03 AM   #8
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I am actually going to extend the wires into my rear run bay and mount the relay there. I crawled up the rig again yesterday and Cummins must have been trying to save money as the pigtail to the lift pump is very short, no good place to get the relay out of the elements so I'll just add wire and put in the bay next to the rest of the ECM fuse holders. I'm going to take the original wiring male portion of the harness, cap the wires and plug it back into the fuel pump to protect the female portion.
I did everything you did except cap the wire ends on the lift pump. I completely bypassed my new FASS pump around the OEM lift pump with new fuel line so I will never use the stock OEM pump again.
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