I have a 1974 Dodge Challenger with a 1973 340 engine. The car originally had a 318 engine. The alternator only has a place for 3 wires to attach to it. However the wiring harness has 4 four wires that go to the alternator. 3 wires are hooked up and one isn't attached to anything. This is how I got the car. The car has a new alternator on it. I think that maybe a 1974 Challenger is supposed to have a different alternator or maybe the 4th wire should be hooked up with one of the other wires.

There is a think black wire attached with a 1/2 nut
There is a blue wire closest to the black wire and the green wire farthest from the black wire all the way to the left. The brown wire is not attched to anything. Is this hooked up right?

see if this helps.
http://www.mymopar.com/downloads/1974/74ChallengerA.JPG

sort of 4 wires, but not all plugged into the alt.

If that brown wire is long, then it might be your carb solenoid or electric choke wire.

I think that you are right. The brown wire is enough to reach the carb. Do you think that the green and blue are in the correct places? Should I have a power at the think black wire where it bolts to the alternator? If so, how many volts should my meter read?

with the key in run, the field wires should both show some voltage.
1 will read close to 12 volts.
the other will read 2 volts ish.

the big wire on the stud will read battery voltage key on or off.

The think black wire reads 0 when the car is turned off. Then reads betteen 13 and 14 when the engine is running.

one of the leads says -0.02 and the other reads .04 when the engine is running

if it reads 13 to 14 while running that would imply charging.

BUT the field readings are bad.

the one that should read 12 volts also feeds the ballast resistor and the sensing line to the voltage reg.
you must have 12 volts or close to it for the balast resistor, so my bet is you have a break in the line somewhere.

check at the vr sensing line and the balast resistor for voltage.

the second field wire is from the vr to the alt. it will be some diminished voltage. but since you aren't getting anything to the other, it is a little suspect.

The blue and the green would go on the (2) alt 1/4" male field terminals. The large black wire goes on the large "batt" alt stud. The black wire must show near batt voltage at all times if it's continuity is kosher & if not there's a prob. The brown wire does not go to the alt but to a nearby sending unit or similar component.

Try pulling the green wire off the alt while running with the blue and large black still attached. The black and blue wire should have battery voltage. Run a jumper wire to ground and momentarily touch it to the field terminal that you removed the green wire from. The alternator should go full charge, around 16V, if it is ok. Dont do this for long as your battery and accesories wont like the access voltage. The problem will then lie in the voltage regulator circuit. You either have a broken green wire, bad ground at the voltage regulator, no power the blue wire to the voltage regulator or a faulty regulator itself. Hope this helps.

Make sure the firewall connectors - heavy red and black from alternator thru gauge and back to battery- aren't corroded - very common problem.

One other thing that you may want to check, take a look at your Bulkhead/Fuse box. press the clips and pull the fuse portion away from the bulkhead. Check to see if the large red primary wire has had a melt down. This is a very common problem and has been an issue on both of my Challengers 70 & 73.

I know that the OE wire coming off the harness by the firewall that runs to the Thermoquad manifold choke is green on a '73.