Lift Pump Wiring questions

[JAG1]

If you go digging around by where your lift pump is (on the block) you will see a two pronged cord, run the positive to a relay the ground to the other side using a real relay set up, then power directly off the PDC. I'll make note on adding this to my FASS guide when i get to finishing it this week.

What he's saying is using the wires that were normally hooked to the lift pump as the ones to activate the relay. When the ecm tries running the pump it will click on the relay instead and then the pump will be connected directly to the batteries inside the PDC box. This way the ECM is isolated from possible harm from high amperage draw if the pump goes binding up.. Mike the mopar man has taught this to all and me too so just repeating what he said. My trouble is I don't trust electrical stuff and want to do this without a relay, more simple =more reliable

[pepsi71ocean]

What he's saying is using the wires that were normally hooked to the lift pump as the ones to activate the relay. When the ecm tries running the pump it will click on the relay instead and then the pump will be connected directly to the batteries inside the PDC box. This way the ECM is isolated from possible harm from high amperage draw if the pump goes binding up.. Mike the mopar man has taught this to all and me too so just repeating what he said. My trouble is I don't trust electrical stuff and want to do this without a relay, more simple =more reliable

what you are describing is the typical wiring setup for a FASS/airdog system. You put the relay on the positive side, and then the Positive voltage from the ECM powers the relay, thus opening the relay up and allowing electricity to flow to the fuel pump. I find that its really hard to kill a relay, and the voltage shouldn't go backwards as they will not be inter connected, so if the fuel pump goes nuts, it won't effect the ECM, just batter or PDC (which ever you hook it up to, The ECM positive runs at i believe 8 volt, or 8 am, (idr), you need to run on 12v@ 20 amp as the FASS 95 runs on 20-25 amp as it has a 30 Am inline fuse in it. Running a full sized fass/ airdog pump will burden the power from the ecm.

[jjr3211]

ok that makes sense to me now i was not sure what to do with the other wire i am guessing that you just do not use it, and would you just ground the punt to the frame?

[JAG1]

ok that makes sense to me now i was not sure what to do with the other wire i am guessing that you just do not use it, and would you just ground the punt to the frame?

I'm still getting this idea together myself, more so now that I hear relays are more reliable. I think there is a ground prong on the relay for the negative wire from the ecm which normally would go to the negative side of the pump.

[ISX]

A relay needs positive and negative to activate the coil, much like anything else. You can't run something with just positive or just negative. The schematic on top of the relay will show a coil symbol and have a connection on either end of the symbol. Those are the ones that get the positive and negative from the ECM to activate the relay. It doesn't matter which one goes where, as long as you end up with positive on one side and negative on the other, it will turn on.

Now the other part of the relay is what it switches on and off. There will be another symbol that shows a light switch looking thing that is not connected or "normally open". It will look like this.

You can see that 85 and 86 are the coil. 30 and 87 are the normally open contacts, you can see the "switch" looking thing between the connections with a dashed line going to the coil showing that it pulls the switch closed to connect 30 to 87. If you have any doubts just show us the schematic of your relay as some are different looking. Anyhow, you hook the PDC positive to one contact and the pump goes to the other contact. Doesn't matter which, it's either connected or disconnected so it doesn't care what it's connecting or the flow of current. Usually 30 gets the power and 87 is the accessory. When the relay gets power, the coil closes the contact between the PDC and the pump so the pump turns on. This does leave the negative of the pump in question, ground it to the frame.

If your relay looked like that, an example would be hook the ECM positive to 85, ECM negative to 86, PDC to 30, and Pump to 87.

Some relays have an 87a, this is a contact that is normally closed, meaning the contacts are closed any time the relay doesn't have power, so don't use that contact.

[JAG1]

Thank you. That is one cool pic that explains it all. Thanks again and I noticed the 40 amp capacity too

[jjr3211]

Ok thanks that's where I was confused I thought you would just ground the relay to a ground point and just not use the other wire and if I am understanding correctly just ground the pump to the frame? Sorry for so many questions I just don't want to burn any thing up.

[ISX]

Ok thanks that's where I was confused I thought you would just ground the relay to a ground point and just not use the other wire and if I am understanding correctly just ground the pump to the frame? Sorry for so many questions I just don't want to burn any thing up.

Yes ground the pump to the frame. I don't know which wire of the ECM turns on and off since I don't own one and nobody will say on this thread which one does so that's why I said use both that come from the ECM, removing all doubt. If it was indeed the positive then you could just run that to the relay and ground the other side to the frame, but I haven't read which one switches from the ECM.

[pepsi71ocean]

Yes ground the pump to the frame. I don't know which wire of the ECM turns on and off since I don't own one and nobody will say on this thread which one does so that's why I said use both that come from the ECM, removing all doubt. If it was indeed the positive then you could just run that to the relay and ground the other side to the frame, but I haven't read which one switches from the ECM.

you would just use the ECM's fuel pump lead. I am somewhat puzzled as to why you wouldn't just hook the negative up to the battery and not the frame. you would want the best connection possible and that would be to run back to the battery.

[ISX]

you would just use the ECM's fuel pump lead. I am somewhat puzzled as to why you wouldn't just hook the negative up to the battery and not the frame. you would want the best connection possible and that would be to run back to the battery.

That works too. I use my frame to start my truck, batteries are in the back, run the positives to the starter and ran a couple negatives from the engine to the frame, works like a charm.