barrattboy72

My NA / 5.0 build is 99% complete. All I have left to do is get the exhaust done.


Just one problem.....

When I connect the battery the fuel pump comes on with the key off and stays running until I disconnect the battery. The jumper wire that was in Martins manual got hot enough to melt the plastic off the wire. Also, the mustang fuel relay next to the EEC is getting warm to the touch. What did I do wrong? Is there a better way to wire the fuel pump?

PS. All the other electrical (lights, horn, etc.) all work fine.

Thanks in advance,

Chris

V8MiataMike

Martin's jumper works independent to anything the Ford EEC would do. He simply has you jumper the Miata +12V "in" to the Miata relay to the +12V "out" (take Miata relay out and jumper the two wires) which should make the fuel pump run when the key is in run mode and start mode only.

I would recommend using the output of the EEC fuel pump relay and run the +12v out from it which would have gone to the Mustang fuel pump over to the wire in that jumpered connector that goes directly to the Miata fuel pump.

barrattboy72

Mike,

Thanks for the reply.

So I assume the mustang fuel pump relay is the one under the hood next to the maf wires? Should I just cut the output wire on it and run it to the Miata 12v pump wire that used the jumper?

MRM331

NO! That is the AC WOT shut off relay. The fuel pump relay was part of another harness that plugged into your main harness. When I build a customer's harness I add a new Ford relay and base next to the ECC relay (near the computer) to run the fuel pump. Tap the yellow (or black/orange) wires running to the ECC relay for power (they are the 12V hot wires), use ECU pin 22 to trigger it and any of the solid red keyed 12v feeds in the harness to power the relay's coil (pin 22 grounds the relay). Run your fuel pump power lead out of the other end of the relay. Make sure to run the power line not only to the fuel pump but also back to pin ECU pin 19 so the ECU can monitor it's current draw.

Or pull your harness out and send it to me...

-Jason

577nitro

Great correct reply Jason, AND a wiring diagram to boot. I may need this in the near future........asI will be stripping everything then reinstalling

barrattboy72

Yes Jason, thank you! This will help a ton!

tbone heller

Get rid of all of the jumper wire/Mazda crap & wire it up as a Mustang fuel pump system. I even used the inertia switch (which makes a great anti-theft switch).

barrattboy72

Jason,

After looking at your post and your diagram I am confused. lol


Could I just build my own fuel pump relay?

87 - 12 volts
30 - 12v key on
85 - pin 22 of eec
86 - to fuel pump?


PS. I wanted to send you my harness but your lead times were way to far out for me.