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Need help 3g alternator problem.

6K views 76 replies 13 participants last post by  tmoss 
#1 ·
Ok, so here is the dilemma. It is an 88 mustang rebuild built 302, custom dash with Marshall gauges with custom wiring, 3g alternator conversion with wire tuck, mud 6aln for ignition, fitech fule injection. All wiring for 3g alternator is correct except there is no dummy light or resistor inline with exciter wire going from gauge panel to voltage regulator built into the 3g alternator. No matter what I do the alternator is jumping all over the place when running with a normal load on it. When I turn off the 150amp DC breaker going from the alternator to the battery source the jumping and shaking stops because it is not sensing a load. I tried a new alternator and had this one tested at an alternator shop and the alternator is good. I posted a video of what it is doing on YouTube for anyone's viewing. Do I need that resistor on the exciter wire to stop this from happening? Please help it is driving me nuts.
 
#5 ·
Like Indy said the belt is ready to be chucked but read below that I do have all wiring correct except the missing 500ohm resistor.

BlackLX as you asked.

I have tested the voltage output from the stud on the alternator and I am within spec of 14.65 volts and tested at battery and multiple other points which are also at 14.65 volts. I have done the 3g conversion about 20 other times and all worked. This is the first one I've done without original dash cluster. So the wiring I have is white wire from pigtail going to the stator plug, the yellow wire from pigtail is going to starter relay b+ (sense wire), green wire from pigtail is going to 12v dummy light feed from original harness which use to go to the dash so the dummy light is gone and it also eliminated the 500ohm resistor which still allows the alternator to charge if dummy light burns out. So all the wiring is correct. Almost forgot, I have 4guage wire going from alternator post (output) to the b+ on starter relay and of course battery is connected to b+ as usual. I also eliminated the old black and orange charge wire from old alternator in which the 4 gauge replaces.
 
#6 ·
that 'dummy' light has to GO TO SWITCHED BATTERY POWER FROM THE IGNITION SWITCH


THE original light and resistor are in parallel, YOU NEED BOTH

the original black orange wire has the feed for that

when people do the conversion, and get rid of the black and orange they NO CHARGE
 
#8 ·
With the black and orange gone the 4 gauge takes care of the charging portion to the battery. I can't be the first to remove all of original cluster, which has the resistor and light built into the circuitry of the cluster panel. Yes the light and resistor are in parallel due to if the light bulb burns out, which they do, the resistor will still allow current to flow on the exciter wire. Could the jumping be due 12v going to the regulator be to much and the 500ohm resistor reduces the voltage which will keep the Alt from jumping all over the place?
 
#9 ·
there is NO CURRENT FLOWING through the bulb and resistor when NOT grounded by the alt

there is therefore NO voltage drop


you know better, guess what is spliced into the blk/orange wires...............that you cannot see!!

If you look at a factory wiring diagram, it will be real evident

do you think the bulb in the cluster is 500ohms?

I guess i dont need to tell you how wrong you are, I said parallel for a reason

go check ohms law
 
#13 ·
According to diagram I use a lot it only has the sense wire going to the black and orange which I know about. This is to sense the load drop to kick up the voltage to charge the battery and keep the correct amount of juice within the system. So anyone and Indy tell me what I am missing here. I know the cluster uses juice but how much does it use?
 
#24 ·
Some dude on stang net was being horrible. The funny things is that I am far from green with auto electrical especially when he was telling me I needed the full load from the original cluster to make it run right. I guess to each his own but all suggestions are very much appreciated.
 
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