Rewired fuel pump now fuel gauge doesnt work

[r32GTSTI6]

So i rewired my fuel pump with a relay and it works only when the ground off the tophat is disconnected (the one in the pic) but then my fuel gauge doesnt work. When that ground is grounded the fuel gauge works but it just blows the fuse that goes between the battery and relay. I have wired the relay according to the diagram in pic 2. What is wrong?

ive checked all the pins about 5 times and theyre exactly how every diagram ive looked at says to do it. Maybe the fuel pump is shorting to the pump cradle or maybe ring terminals on the inside of the tophat are shorting against the cradle?

[KiwiRS4T]

The diagram you are using is no good for an RB

86 and 87 need to be power from ignition switch and earth through ecu (not to ground) respectively.

If you go to the tutorials section you may find a guide to the colours of the wires coming from the front of the car.

[r32GTSTI6]

6 hours ago, KiwiRS4T said:

The diagram you are using is no good for an RB

86 and 87 need to be power from ignition switch and earth through ecu (not to ground) respectively.

If you go to the tutorials section you may find a guide to the colours of the wires coming from the front of the car.

I did pin 86 to the ecu switch to turn the relay on and it works now. I think the bulkhead was shorting to the fuel cradle because i didnt drill the hole enough. Are you sure pin 87 is wrong though? Even the guide I found on sau had 87 as the power wire for the pump

 

[GTSBoy]

There have been a couple of threads lately where this has been discussed.  This link is to a post of mine showing the R34 fuel pump circuit (which, if not the same as R32, is going to be same enough with respect to where the power comes from and how the OEM fuel pump relay is triggered by the ECU). https://www.sau.com.au/forums/topic/476054-r34-gt-na-fuel-pump-wiring/?do=findComment&comment=7898530

The short version is that the ECU provides the earth for the relay to switch the pump on.  Not the power.  The earth.  Look to the left of the red box on my post.  The fuel pump is the first thing to the left, then the relay is the next thing to the left.  If you look at the coil on the relay, pins 1 & 2, you will see that pin 1 is connected to the ECU pin 13 (remember, this is R34, I haven't checked if the ECU pin # is the same on R32, not that it matters for this discussion).  Pin2, the other side of the coil, comes from the 15A fused power supply for the whole pump.  That makes the ECU side of the relay's coil the earth side.  ECUs almost always provide a switched earth, rather than a switched power supply.

So, for your own new relay installation, you need to power the coil from a fused supply and the switched wire from the ECU is actually the earth.  This is what you have now done by connecting pin 86 to the ECU's pump control terminal.

That circuit in the black backgrounded image above would have an earth on both sides of the relay's coil** and shouldn't do anything.  The only way that circuit can work is if you use the original pump power wire (switched by the original relay) to power the coil to switch your new relay on.

** and this is why you were blowing fuses - because you were connecting the power supply direct to earth.

Edited March 6, 2019 by GTSBoy

[r32GTSTI6]

38 minutes ago, GTSBoy said:

There have been a couple of threads lately where this has been discussed.  This link is to a post of mine showing the R34 fuel pump circuit (which, if not the same as R32, is going to be same enough with respect to where the power comes from and how the OEM fuel pump relay is triggered by the ECU). https://www.sau.com.au/forums/topic/476054-r34-gt-na-fuel-pump-wiring/?do=findComment&comment=7898530

The short version is that the ECU provides the earth for the relay to switch the pump on.  Not the power.  The earth.  Look to the left of the red box on my post.  The fuel pump is the first thing to the left, then the relay is the next thing to the left.  If you look at the coil on the relay, pins 1 & 2, you will see that pin 1 is connected to the ECU pin 13 (remember, this is R34, I haven't checked if the ECU pin # is the same on R32, not that it matters for this discussion).  Pin2, the other side of the coil, comes from the 15A fused power supply for the whole pump.  That makes the ECU side of the relay's coil the earth side.  ECUs almost always provide a switched earth, rather than a switched power supply.

So, for your own new relay installation, you need to power the coil from a fused supply and the switched wire from the ECU is actually the earth.  This is what you have now done by connecting pin 86 to the ECU's pump control terminal.

That circuit in the black backgrounded image above would have an earth on both sides of the relay's coil** and shouldn't do anything.  The only way that circuit can work is if you use the original pump power wire (switched by the original relay) to power the coil to switch your new relay on.

** and this is why you were blowing fuses - because you were connecting the power supply direct to earth.

Ok I just went out and rechecked my relay and this photo is EXACTLY how I have wired mine in:

Everything is working with it wired exactly in this diagram but how!? Pin 86 isnt a +12v like it says in the diagram so how is the relay getting a signal to turn on? Basically im asking if its safe to keep driving or am I going to go up in flames

[r32GTSTI6]

My pin 86 is the yellow and black wire (r32 gtst)

[GTSBoy]

If your wiring is as you say, pin 86 is connected to the old pump wire from the original relay....ie, the wire that used to originally actually power the pump, then, when the ECU activates that original relay, that will then power your relay.  It's arse backwards (a bit) and double the chance of a failed relay stopping you by the side of the road, but it will work.

2 hours ago, GTSBoy said:

The only way that circuit can work is if you use the original pump power wire (switched by the original relay) to power the coil to switch your new relay on.

As to your wiring between pin 30 and 87, you have that backwards.  But it will still work.  These are just the 2 terminals that are either side of the switched contact.  It's just that we conventionally put 12v INTO pin 30 and have it come out 87.  It's just a convention when wiring relays. 

Edited March 6, 2019 by GTSBoy

[r32GTSTI6]

4 hours ago, GTSBoy said:

If your wiring is as you say, pin 86 is connected to the old pump wire from the original relay....ie, the wire that used to originally actually power the pump, then, when the ECU activates that original relay, that will then power your relay.  It's arse backwards (a bit) and double the chance of a failed relay stopping you by the side of the road, but it will work.

But it cant be because the original fuel positive is the white and purple wire which went to the tophat and connected direct to the fuel pump positive.

4 hours ago, GTSBoy said:

  It's arse backwards (a bit) and double the chance of a failed relay stopping you by the side of the road, but it will work.

Are you saying that the original power wire is now acting as a switch to turn on the relay or is it acting as the power source for the pump ? Because if it is acting as the power source for the pump wont it be too small to hold the amps that a walbro 460 (what I have just installed) would draw?

[GTSBoy]

7 hours ago, r32GTSTI6 said:

the original power wire is now acting as a switch to turn on the relay

This

[r32GTSTI6]

2 hours ago, GTSBoy said:

This

Oh ok well if im correct (long shot) that means there should be no problem leaving it how it is? Other than obviously two relays which can fail.

[GTSBoy]

Yup.