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> Fuel pump wiring in a 6 conversion - non relay board, Is a relay needed?
nditiz1
post Sep 8 2021, 01:12 PM
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So I'm not using a relay board in my 6 conversion. I have cut the 14 point harness where it branches to the trunk, so maybe just 2 ft off the end. I left the starter wire the full length. In hindsight I should have left the tach and idiot light wires just as long, but it's OK, enough to butt splice. Anyway, there are 2 red wires(switched 12 volts) I was planning on 1 for the ECU and have the other kick on the fuel pump. Is there any reason I need to run a relay for the fuel pump?
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Steve
post Sep 8 2021, 02:26 PM
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The ignition switch is pretty wimpy and Porsche always ran a relay for the pump. I would add a relay or worse case use fuse 8, which is already on a relay.
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Dustin
post Sep 8 2021, 02:43 PM
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The relay is there to prevent the current that the fuel pump draws from going through the ignition circuit. Porsche/VW is telling you in their design that you don't want that current there. Turning the relay on doesn't use very much current.
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ClayPerrine
post Sep 8 2021, 02:47 PM
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Put the fuel pump up front.

Put a relay in above the fuse box to turn on the fuel pump.

Trigger the relay off the ignition fuse (#8)
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Steve
post Sep 9 2021, 07:07 AM
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QUOTE(ClayPerrine @ Sep 8 2021, 01:47 PM) *

Put the fuel pump up front.

Put a relay in above the fuse box to turn on the fuel pump.

Trigger the relay off the ignition fuse (#8)

(IMG:style_emoticons/default/agree.gif)
I installed two relays up front. One for the cooler fans and one for the pump.
Easily accessible. Mine is a 75, so the pump was already up front.
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IronHillRestorations
post Sep 9 2021, 10:29 AM
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+1 on Clay’s advice. Fuel pumps do better pushing than pulling
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SirAndy
post Sep 9 2021, 11:10 AM
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QUOTE(nditiz1 @ Sep 8 2021, 12:12 PM) *
I have cut the 14 point harness where it branches to the trunk

Why???
(IMG:style_emoticons/default/confused24.gif)
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nditiz1
post Sep 9 2021, 12:50 PM
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QUOTE(SirAndy @ Sep 9 2021, 10:10 AM) *

QUOTE(nditiz1 @ Sep 8 2021, 12:12 PM) *
I have cut the 14 point harness where it branches to the trunk

Why???
(IMG:style_emoticons/default/confused24.gif)


I didn't like it (IMG:style_emoticons/default/biggrin.gif)

Mainly because I'm not using the relay board and the connector was already in pretty bad shape. The connectors from Porsche are around $25. So $50 (both ends) to bridge 2 sets of wires. I think I'm only using 5, tach, oil pressure, backup lights (2), switched power.
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Spoke
post Sep 9 2021, 08:12 PM
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QUOTE(nditiz1 @ Sep 8 2021, 03:12 PM) *

I was planning on 1 for the ECU and have the other kick on the fuel pump. Is there any reason I need to run a relay for the fuel pump?


Will the ECU turn on/off the fuel pump like the OEM ECU does? It's usually not good to have the fuel pump come on with the ignition since if in an accident or a fuel line ruptures the fuel pump will continue to operate.
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mepstein
post Sep 10 2021, 05:22 AM
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QUOTE(Spoke @ Sep 9 2021, 10:12 PM) *

QUOTE(nditiz1 @ Sep 8 2021, 03:12 PM) *

I was planning on 1 for the ECU and have the other kick on the fuel pump. Is there any reason I need to run a relay for the fuel pump?


Will the ECU turn on/off the fuel pump like the OEM ECU does? It's usually not good to have the fuel pump come on with the ignition since if in an accident or a fuel line ruptures the fuel pump will continue to operate.


That happened to a member here on a freshly done six conversion. Engine caught fire, fuel pump continued to run.
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nditiz1
post Sep 10 2021, 05:38 AM
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It does not, I think I can tell microsquirt to do it that way. So I can use one of the red wires in the engine compartment to supply power to the relay and the signal can come from the ECU.

@VaccaRabite - is that how you have your megasquirt setup?

Also, what is supplying the power to the two red wires and 1 black wire in the 14 point harness? Somebody mention to not run it through the ign switch. Just want to make sure these are not tied to it. The relay board schematics do not state where those wires go to.
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ClayPerrine
post Sep 10 2021, 05:40 AM
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If you are running Megasquirt, put the relay board back on the car. Use the factory relay to turn the Megasquirt ECU on, and the factory fuel pump relay. They both come off the 4 pin connector on the left rear of the relay board.

Here is an image of the relay board that may help you.

(IMG:http://www.914world.com/bbs2/uploads/post-1143-1610637417.jpg)
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nditiz1
post Sep 10 2021, 06:28 AM
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Thanks Clay. Very helpful, more than the one from the workshop manual.

I'm too far down this path of removing the relay board/mounts/cutting the harness to go back.

I will need to double check the red wires, I thought they were switched on, but this shows they are battery.
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VaccaRabite
post Sep 10 2021, 08:13 AM
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For my Microsquirt the fuel pump works exactly like DJet - it runs for a second or so when you turn the key, and will shut off if the ignition turns off.

My system has a small fuse panel that gets power from the plug off the relay board at the very bottom left, from port IV in the diagram Clay posted (I think thats the one - its one of those 4.)

Zach
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nditiz1
post Sep 10 2021, 10:07 AM
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Ok wired it up on my test stand through the microsquirt and all is good. Thanks everyone.
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