Help Fixing wiring on an SPX with Weber Swap

[CoSut]

Took this SPX in as a project because I wanted to save it, but its my first 2.6 MM. This is how the original owner has it wired, but the wire to the fuel pump it burning, about a yard of wiring that I had to cut out. From what I've traced I see NO relay in this set up, which seems odd to me. what I find interesting is that the burning is isolated to only the wire heading back to the pump (thankfully). I see no damage up into the harness (so maybe not a relay issue?). They had no protection on the wiring it was just hanging in the open with one or two zip ties, that were a bit too snug, so maybe it just broke open and was arcing on the metal. Maybe the 16 Ga isnt heavy enough.

So im looking for some input from those who have done this swap. Im sure that empty plug was a relay. the choke and pump are running into the same pin which according to the diagram is the Auto Choke. I see a heavier gauge black/white stripe that is listed as Slow cut, can this be utilized?

I wanna get a relay and fuse worked into this so its a safe reliable setup. Any help would be great thank you!!!

Also I would love to get enough info to put together a comprehensive diagram/schematic/part number PDF to upload to the site for anybody else since this seems to be a popular swap.

[CoSut]

I also wanna mention that I have no Idea what fuel pump they used, but when I get a warmer day I intend to pullthe bed off the truck so ill check then.

[SubGothius]

That loose connector block would have gone to the stock Mikuni carb's feedback computer/controller box, which the PO apparently removed along with the Weber conversion as it's not used/needed in that case. It's fine to leave that connector as-is.

There was no original relay, as the stock carb used a mechanical fuel pump driven by the cam in the head. Those mech pumps output fuel pressure too high for a Weber, and adding a pressure regulator to the mech pump tends to stress the pump until it fails, so most folks add a low-pressure aftermarket electric pump for a Weber conversion.

Looks like the PO wired the electric pump and choke to be powered directly from a wire in the Mikuni's connector block, rather than having that just trigger a relay. 16 gauge wire was prolly fine to power the pump; I used 14 ga. just because I already had a whole spool of it handy. Most likely that power wire simply had its insulation melted/abraded away somewhere it could touch a ground, causing a hard short that burned the wire. I'm not sure I'd trust the wiring to that Mikuni connector anymore, so I'd just have the relay triggered by the key-on power terminal on the ignition coil's resistor block (this would be the terminal that already has black wires with a white stripe connected to it).

Relays typically have terminals numbered according to a DIN standard, so here's how you'd hook those up:

• 85: To ground;
• 86: To a key-on power terminal;
• 87: To the pump;
• 87b: To the choke;
• 30: 10A fused wire from battery (+) terminal.

85 and 86 are the trigger circuit and can be swapped around, whichever is easier/tidier wire routing for you. 87b is just a duplicate of 87, so if you don't have 87b, just wire 87 to both the pump and choke. If you have an 87a, that will be left unconnected. There should be a threaded hole (maybe with a bolt still in it) in the inner fender near the battery where the old feedback computer/controller box used to be mounted; that's a good place to mount the relay, and you can use that point as your relay ground as well.

[CoSut]

That diagram matches the relay I picked up so, I DO want a line off the battery with a fuse to 30 and run the BW wire (Slow-Cut Solenoid) to 86 on the relay. Just wanna verify im looking at this correct, because I was confused that its current setup isnt running any power from the battery, but rather the ignition. on this setup I draw a line to the relay off the battery.

[SubGothius]

Yes, the PO's setup wasn't relaying power direct from the battery to the pump, just powering the pump via an ignition-switched circuit on that Mikuni connector. I'd say just skip using that connector at all, and instead trigger the relay from the key-on terminal at the coil's resistor block. That's the white ceramic thing attached to the coil; one end of that is wired to the coil, and the other end is wired to key-on power, so the latter is what you'd wire to terminal 86.

[CoSut]

I was finally able to get the wiring done today. Shes cranking healthy, got 12v everywhere I need it, and I can feel the relay working, but its not firing.

The pump sounds a bit loud to me and the fuel pressure is reading a bit high between 4-5 I think it was. My best guess is ice in the line, I dumped some Heet in, gonna try getting back to it tomorrow. if anybody has a suggestion on something to check let me know. hopefully its just the cold weather.