Car runs with ignition switch wire not connected - mystery?

[stuartrubin]

I just installed an aftermarket ignition switch. I followed the various instructions, combined the wires to get two bundles into the #15 connection, etc. Everything seems to be a right except there is one bundle of a Gray + Green/black stripe which does not seem to want to go anywhere.

I have a '75 which did have the rare #16 connector on the switch and I believe from my old notes that this bundle was in fact connected to #16. But the new switch has no #16 and this bundle is just dangling.

But, I cranked up the engine and things seem to work fine without it! In truth, I have not done an exhaustive test, nor have I actually driven the car, but the engine starts, runs (at least when I pump gas pedal, but that's another issues), headlights work, radio, etc. I hear the fuel pump running (at least I think it's the fuel pump making a whining noise from the trunk).

Exterior/parking lights?

Fuel pump really that i don't have?

So what gives? Should I just drive it and not worry about it?

Thanks

Stuart

[SteinOnkel]

Beep it out and trace it.

[spider2081]

I have a '75 which did have the rare #16 connector on the switch

I'm thinking the cars that need ignition switches that have a terminal 16 have an electric fuel pump. The fuel pump has a safety feature that operates off the oil pressure switch. if no oil pressure the fuel pump gets no voltage to operate. In order for the engine to start the fuel pump gets voltage from terminal 16 in the "start" position of the ignition switch.
If your car has a mechanical fuel pump you ignition switch doesn't need a terminal 16.
If you have an electric fuel pump maybe a previous owner bypassed the safety circuit.

[stuartrubin]

maybe a previous owner bypassed the safety circuit

This is actually my suspicion. The PO (or maybe some P^nO) did a few weird things electrically. I'll try to trace it visually and buzz it out with a meter and see what rabbit hole it takes be down.

In the short term, I just want to make sure this isn't some critically crazy circuit, like the "you're car will explode if disabled" wire...

Thanks!

[18Fiatsandcounting]

I believe spider2081 has it right. Terminal 16 is connected to power (terminal 30, the brown wire) only in the start key position. This was used to provide power to the electric fuel pump when starting the car, and also for operating the relay that controls the dual point ignition if the car has that. After starting, the "normal" electrical system took over to operate the fuel pump and ignition system.

The '75 electrical diagram that I have shows a green-black wire from the ignition switch to the fuel pump.

The gray wire is somewhat of a mystery to me, but maybe that was for the dual point relay? I don't see that on the diagram that I have, though...

-Bryan

[18Fiatsandcounting]

The gray wire is somewhat of a mystery to me, but maybe that was for the dual point relay?

I stared at some more wiring diagrams that I have for mid-70s spiders, and I think I have the gray wire figured out. The green black wire from the ignition switch terminal 16 goes to a connector C23 where it goes 2 places: continues as a green/black wire to the fuel pump, but also connects to a gray wire that goes to the fuel pump relay and ultimately to +12V. So, either the P^nO moved the gray wire from C23 to connect directly to terminal 16 (same result electrically), or Fiat did it this way originally.

My guess is that Fiat wired it this way originally, and my wiring diagram is correct electrically but has a slight error in where the green/black and gray wires come together for the fuel pump.

-Bryan