Fuel Pump Wiring...
Thread Starter
Senior Member
Joined: May 2003
Posts: 989
From: Dover DE
[b]Ok guys, I was asked how to wire in a twin fuel pump setup
Using 2 Bosch 40amp relays I will try to explain using a few pictures and step by step instructions.
In this picture is the typical wiring for a Bosch relay
So in order to make things simple, we will use the factory wiring that goes to the fuel pump and run seperate relays for each pump. This may sound like a little overkill, but I would rather overkill the setup, than try to run too little power to the pumps and risk running lean.
Terminal 86: will be the stock fuel pump positive (12v +) going to the pump now, trace this wire from the fuel pump access plate back along the harness until you find a convienient spot to mount your relays. Colors may vary over the years so please consult the correct Factory Service manual for your model and year. Cut this wire and attach the wiring harness side (from the car, not the pump) to the terminal
Terminal 85: run a new wire from this terminal to the chassis make sure you use a clean spot, preferably using sandpaper to go to bare metal.
Terminal 87: connect with a 10ga or 12ga wire from relay to the fuel pump positive wire (match the wire your fuel pump is supplied with)
Terminal 30: Connect this wire directly to the battery positive. I would highly reccemend using a fused power wire from a stereo amp wiring kit, this assures enough power over the distance traveled to the relay.
The process above is then repeated for fuel pump #2, the only difference will require you to splice the main harness positive wire to both relays, there will be minimal current draw through this wire in comparison to the draw created by the fuel pump. Then ground the pumps individually to chassis ground. Make sure you have bare metal when grounding, the better the connection, the better the power is transferred.
You may have to get creative with the wiring through the pump access plate. Check with your local electronics supplier for insulated terminals. you will need a positive and negative terminal for each pump, allowing you to transfer the power through the plate to the relays, the stock wiring is too small to handle the large load of direct current from the battery. (example: 10ga from relay to factory 18ga back to a 10ga for the fuel pump) Now you can do variations of the above example, but I am not garunteeing it to work.
With the setup above your fuel pumps will receive direct battery voltage, as some know the factory wiring in our cars is not the greatest and you can get a voltage drop of 1-3 volts through all of the factory wiring to the fuel pumps. By "Hot wiring" the fuel pumps your pumps will be operating at the voltage the alternator is producing. If you look at the manufactuers specifications for the fuel pump you are using it is usually listed at a voltage higher than the factory wiring will produce, so if using the factory wiring to run the pumps, you are not getting the full advantage of upgrading to a larger fuel pump.
For example, if the pump is rated @ 255 liters per hour @ 13.5 volts you may only be getting 12.2 volts to the pump through the factory wiring.
Comments and questions are all welcome. There are easier ways to do this, just not nessecarily better....
Using 2 Bosch 40amp relays I will try to explain using a few pictures and step by step instructions.
In this picture is the typical wiring for a Bosch relay
So in order to make things simple, we will use the factory wiring that goes to the fuel pump and run seperate relays for each pump. This may sound like a little overkill, but I would rather overkill the setup, than try to run too little power to the pumps and risk running lean.
Terminal 86: will be the stock fuel pump positive (12v +) going to the pump now, trace this wire from the fuel pump access plate back along the harness until you find a convienient spot to mount your relays. Colors may vary over the years so please consult the correct Factory Service manual for your model and year. Cut this wire and attach the wiring harness side (from the car, not the pump) to the terminal
Terminal 85: run a new wire from this terminal to the chassis make sure you use a clean spot, preferably using sandpaper to go to bare metal.
Terminal 87: connect with a 10ga or 12ga wire from relay to the fuel pump positive wire (match the wire your fuel pump is supplied with)
Terminal 30: Connect this wire directly to the battery positive. I would highly reccemend using a fused power wire from a stereo amp wiring kit, this assures enough power over the distance traveled to the relay.
The process above is then repeated for fuel pump #2, the only difference will require you to splice the main harness positive wire to both relays, there will be minimal current draw through this wire in comparison to the draw created by the fuel pump. Then ground the pumps individually to chassis ground. Make sure you have bare metal when grounding, the better the connection, the better the power is transferred.
You may have to get creative with the wiring through the pump access plate. Check with your local electronics supplier for insulated terminals. you will need a positive and negative terminal for each pump, allowing you to transfer the power through the plate to the relays, the stock wiring is too small to handle the large load of direct current from the battery. (example: 10ga from relay to factory 18ga back to a 10ga for the fuel pump) Now you can do variations of the above example, but I am not garunteeing it to work.
With the setup above your fuel pumps will receive direct battery voltage, as some know the factory wiring in our cars is not the greatest and you can get a voltage drop of 1-3 volts through all of the factory wiring to the fuel pumps. By "Hot wiring" the fuel pumps your pumps will be operating at the voltage the alternator is producing. If you look at the manufactuers specifications for the fuel pump you are using it is usually listed at a voltage higher than the factory wiring will produce, so if using the factory wiring to run the pumps, you are not getting the full advantage of upgrading to a larger fuel pump.
For example, if the pump is rated @ 255 liters per hour @ 13.5 volts you may only be getting 12.2 volts to the pump through the factory wiring.
Comments and questions are all welcome. There are easier ways to do this, just not nessecarily better....
Senior Member
Joined: Dec 2002
Posts: 4,107
From: fredneck MD
I just wrapped up the install of the twin pumps.
It works awesome so far. I have only primed the fuel pumps, but they put out 40psi easily.
Seans instructions were easy to follow. This will def. help me in the future! Ill get a pic tonight.
It works awesome so far. I have only primed the fuel pumps, but they put out 40psi easily.
Seans instructions were easy to follow. This will def. help me in the future! Ill get a pic tonight.
Thread Starter
Senior Member
Joined: May 2003
Posts: 989
From: Dover DE
Glab I could help, one thing I forgot to mention, for those of you that are planning to do this, you need to make sure you check the fuel pressure again after starting the car, with the way this sytem is wired if your fuel pressure regulator was set using the factory wiring and you have increased the voltage by "Hot wiring" the fuel pump(s) like this the pressure may increase...
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