No power to fuel pump, Tracing Black/Yellow fuel pump wire Options

[Creamsicle New Zealand]

Hi all, hoping someone may be able to help me with no power to fuel pump issue.
1974 914 I have traced the Black/Yellow wire from back of car to relay on the fuse panel at front of car. I have changed relay with two others I know work but still no power to the Black/Yellow wire. Large Red wire to relay has power all the time. Red/White wire to relay has power when ignition is on.
I'm now at a loss as too were to go to from here. I have looked for colored wiring diagram but not able to find one.
Does anyone have any ideas please?
Thanks Steve

[davep]

I do not recall a yellow wire going to the fuel pump connector. The wire connectors in the plug often fail, and I built new harnesses with larger wires than stock. Also, the computer, if used, also controls the the relay and it depends on the pulses from the distributor trigger points to know when the engine is spinning and thus requiring fuel.

[Superhawk996]

What you’re describing is likely a prior owner cobble job.

The stock fuel pump wire is black with red tracer.

It is fed from a relay in the engine compartment from the relay board.

All the wiring diagrams in the Haynes and Factory manual document the wire color codes.

You’re just going to have to physically trace and test with a multi-meter.

[Creamsicle New Zealand]

Thanks for the input. Previous owner changed location of fuel pump to under the fuel tank, they also placed the fuel filter between fuel pump and engine, should have put the filter between tank and pump (IMG:style_emoticons/default/headbang.gif) . As a result, fuel pump stopped working due to shit in the tank. The pump should start for couple of seconds as it builds up pressure when ignition is turned on, this is not happening, there is no power to the pump positive wire along its path I have so far found.
Does anyone have a colored wiring diagram they could flick thru please? I'm going to need to spend hours doing a full trace as per Superhawk996 sugestion.

[Superhawk996]

If you’re still running FI and pump used to cycle for a couple seconds, the relays that control it are in the engine compartment.

Here is a color coded copy of the relay board that was colorized by Clay.

There are two relays involved

First the power supply relay that activates at key ON. This relay supplies power to the fuel pump relay solenoid.

Then then fuel pump relay
The fuel pump relay is controlled by the ECU via the 4 pin connector terminal III that applies a ground coming from the ECU to activate the pump relay.

Check the 25a fuse to make sure it isn’t corroded and is transferring power to the fuel pump relay.



Although the graphic references 73’ the 74’ relay board works the same way.

[SirAndy]

Not exactly what you're looking for but the relay board pic at the end might be helpful to see if you have power in the right places on the relay board.
http://www.914world.com/specs/SirAndyCarbFuelPumpRelay.php

You should also be able to bypass the FI brain there to test the wiring to the pump and make sure the issue is not with the board or brain or the engine harness to the brain.
(IMG:style_emoticons/default/idea.gif)

[Creamsicle New Zealand]

Awesome, thanks guys. I'm into it now, will let you know the outcome.

[wonkipop]

go here.
pdfs of the full factory manuals.
colored elec diagrams are in the electrical volume.

http://p914-6info.net/Manuals.htm

you can download each of the volumes separately.

[Creamsicle New Zealand]

Thank you everyone...SUCCESS... I have no idea what exactly the problem was. I removed the relay board, relays etc., sprayed contact cleaner and wiggled all the connectors I could find, reassembled everything then turned the key and heard that familiar sound of the fuel pump pressure up. (IMG:style_emoticons/default/biggrin.gif)