Three-Fifty...Everything built after the 6 volt era usually has a resistor wire built into the harness...I call any wire that is turned off by the ignition switch a "Switched Wire "...All will have 12V except for the wire to the coil.It is cut down to about 8V..So if you already have a 12V system and want to add a resistor you can't use the existing wire to the coil..You need a 12V switched wire...A voltmeter is without a doubt a handy tool..On some Chevy trucks etc..there is sometimes a non fused IGN. terminal in the fuse block that is switched... The ignition switch should have an accessory terminal too that would work..One wire to one side of the add on resistor..One wire from the other side of the resistor to the + side of the coil..And of course one wire from - of the coil to the distributer..One wire from the "I" treminal of the solenoid to the + side of the coil..There is a disc in the solenoid that while activated sends a full 12V to the coil while cranking..I had an inline Chevy six once that wouldn't shut off one day.The battery cable at the solenoid had come loose touching the "I" treminal feeding the coil a full twelve volts..That sent me reeling for a few..Concerning your trucks alternator you need to post what kind it is...Built in regulator or remote ??..One wire Delcos work the best..I just put one on a Ford Falcon six cylinder..Made a new car out of it..Keeps the voltage up there better...Thanks for listening...Al...