Why did they make it this way?
The Field Fix harness bypasses the "dead bulb dead battery" scenario.
So is the field fix harness a replacement for the resistor bulb?
Well let's see: The alternator field requires a certain amount of exciter voltage that is supposed to be provided through the bulb. Any electrical solenoid(such as the stock wastegate controller) requires voltage to operate. The kit in question is supposed to supply the field with the proper voltage, should the bulb fail, and requires voltage to do that. The Wastegate solenoid connector was probably the easiest/most convenient source of ignition key controlled(via the ECM/SOL fuse) voltage.It's supposed to keep the alternator's field windings energized in the event that the bulb burns out, thereby keeping you from being stranded by a bad light bulb. How it accomplishes this by being plugged into the wastegate solenoid plug is beyond me though...waiting for an answer on that myself.
I believe it's supposed to be a resistor type bulb where current can still pass even if it burns out. Someone may have installed the wrong type of bulb, and then it will be an issue.
No such bulb exists. When the filament burns out, the bulb is an open circuit.
Not true. How do you think those Christmas lights work that if the bulb burns out only one light goes out but if you pull the socket about 20 lights go out? I don't think that's the type of bulb the circuit is designed to use and I'm not entirely sure they're called resistor bulbs, but they do exist.
Edit: FWIW I think the part in that type of bulb is called a shunt. I remember seeing it on an episode of how stuff works or history of the Christmas light or something like that.
OK, I'll simplify it. The bulb is a standard dash illumination bulb, but *some* cars use a special bulb socket with a resistor built into it. The reason is, if the bulb burns out, the resistor takes over. Well, that's theory.
Now, some reality.
The fault only sometimes lies in the bulb itself. Most of the time, though, it's the socket and/or the flex PC board that makes the attachment to the wiring harness, and ultimately, to the alternator. If the flex board fails (and I've seen many failures with them) then even if the bulb is working, the circuit is interrupted in-between the alternator and the power source - so you call the flatbed.
The FieldFix harness bypasses the bulb using another circuit within the alternator's regulator. It simply picks up power from the positive feed on the WG SOL circuit, so even if you don't use a wastegate solenoid, you can still use its connector for a power source, then route it to the proper input of the regulator. This positively assures that the alternator will put out a charge when the engine is running.
Unless, of course, the SOL fuse is burned out. Then all bets are off.
The FieldFix is a good thing to have, and cheap insurance. Especially if you already have called the flatbed to get your car, or been through the usual "maybe it's the alternator, I'll just replace it" and "maybe it's the battery..."