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Another 3G question

T

Triton

Member
I am a little confused about how to wire the yellow wire on the 3g alternator. After a lot of searching there seems to be two different thoughts or methods about where to connect the yellow voltage sensing wire.
A lot of sites say connect the yellow wire back to the battery connection on the alternator.

Others say connect it back to the starter solenoid.

I have relocated my battery to the trunk and I rewired the car with a Quick Wire 14 circuit harness, my 3g alternator is wired with 2 gauge wire to a distribution point by the fuse block then a 4 gauge wire back to the trunk to a 150 amp fuse.

Method 1:The method that connects the yellow wire back to the alternator’s positive post senses just the voltage output of the alternator, and adjusts output to run power and charge the battery. Some concerns are that with this full alternator output may overcharge the battery making the battery or regulator pre-maturely fail. I have seen anywhere from 125 to 200 amp fuses protecting the charge wire and some diagrams show a 20 amp fuse on the yellow wire.

Method 2: According to Mad Electric, the yellow wire needs to be connected at the distribution point so the regulator can sense a lower voltage from system demand and adjust as needed, then a smaller 10 gauge tuff wire is used to charge the battery. The smaller wire works fine because the battery can only take so much power when recharging and the resistance in the smaller wire keeps the battery from boiling over. Also I don't see a fuse in this system.

So what is the best way to hook this alternator up?
 
Electrically speaking, the connection point is identical whether the yellow wire is connected at the alternator post or the solenoid. The only "difference" if you really want to split hairs is the voltage drop due to resistance from the charging cable between alternator and the solenoid. It would be so minimal though it would not affect anything (I'm talking millivolts here!).


p.s. Regarding the MAD Electrical recommendations, I went to (what I believe to be) the website so see what you're referring to. From what I could find, the information they post is in regards to a GM one wire alternator, not a 3G (unless I missed something!). I believe their recommendation for the smaller gauge main charging wire is due to lower amperage output alternators. I would NOT recommend using 10ga for your main charging wire, you need something bigger.
 
I read the Mad electric article several times and from what I gathered he does not like the 1 wire setup. He uses a delco alternator with the same connections as the 3 g but that alternator does put out less amps (75 amps). I will stick with a 4 gage wire!
What fuse do you think I should use? I read another post that said blowing a high amperage fuse (175) is not going to be instantaneous especially since the alternator is rarely at full output. That post suggested a 125 amp fuse.
I guess it won't hurt to fuse this yellow wire so would a 20 amp fuse be ok?
Thanks
 
Keep in mind when it comes to figuring out what fuse to use in a system (whether your main charging wire or the sensing wire), they have to be based on the system design. By design I mean what the normal operating amperage of the system is designed at (to include all components and wiring). If an engineer did their job properly, each item is designed to a higher level of operating than the rating. This allows a buffer to allow for spikes and surges. A fuse is figured along the same design protocol. IIRC it is based on the normal operating amperage plus 25% (Randy please correct me if I'm off on this...I wasn't an engineer!).

The reason I elaborate so much is to address both of your fuse questions. In other words, I couldn't, and wouldn't answer yes or no to a 20a in the sensing line. Would a fuse inline there help? Maybe. I personally have no plans to fuse the sensing wire on my 3G. My justification for this is; if something is going to cause a problem on this circuit it'll most likely be from within the alternator. If so, the alternator will need replacement fuse or not (on that wire).

Regarding the fuse in the power supply line, I can see one thing from both posts you referenced...neither poster knew crap about electricity! Unless a fuse is specifically designed as slow acting fuse (e.g. a slo-blo or thermal), they blow when their amperage rating is reached (for most the amp rating +/- 5%)...period! At 175 amps it'll not only blow, it'll create a pretty good mini lightning bolt...instantly!!! The other reply, 125a fuse in a 130a rated system...why?!! Will it hurt? No. But it won't allow for any slight surges above rated amperage of the system either. In other words, plan on replacing fuses occasionally and wondering if something IS really wrong! A 175a fuse in a 130a output system is a little high, but they make fuses in specific ratings and you have to work within what's available. If my recollection is correct about the 25% addition, then the "correct" fuse would be a 160a. I don't think you'll easily find one at that rating. I'm sure you could find one (somewhere), but generally the 175a is easier to locate.
 
Ponyman is right. I know how ford designed fuses (slo-blow), approximately 100% of nominal current usage, but I do not know what the surge currents are in any of the Mustang systems.
 
thanks for your info, I'm getting a better hold on how this should work, I just didn't want to do something that others have copied and reposted on the Internet without further investigation!
 
"Triton" said:
thanks for your info, I'm getting a better hold on how this should work, I just didn't want to do something that others have copied and reposted on the Internet without further investigation!
Click to expand...

You're quit welcome. You're also a wise man! Not for listening, but for questioning! There's a lot of knowledgeable people that post really good and helpful info out there. Hell there's many of them right here on Stangfix! I just try to do my part helpin' out when I can! :yah

Good luck with your install.....and remember, PICTURES!!!
 
Instead of making a new 3g thread, thought I would post my question in here since this thread answered my question about the yellow wire.

I have read elsewhere that you should not use the stock ammeter when running an upgraded 3g as the gauge and gauge wiring can't handle it and the high amperage would potentially be dangerous. Question is: how do you disconnect the gauge? I see two ring terminal connections on the battery side of the starter solenoid that are coming from stock wiring. Is one of these the power to the ammeter?

Also, what do I do with the wiring associated with the stock voltage regulator. I simply unplugged the regulator and removed it. Can the wiring that went to the VR be left in place and simply taped over?
 
Well I wired the charge wire in 2 ga. from the 3g to a junction stud in the engine compartment then outside the fenders to another junction stud inside the car on the passenger side, then in 4 ga. back to the battery in the trunk. My next question is I am going to put the MSD ignition under the dash on the passenger side as well, MSD insist that the battery hot and ground has to be connected at the battery. Is this just a generic answer or with my setup can I just connect it to the junction stud? I don't see what the difference would be!
 
"jonward786" said:
Which is great for people who want to retain the stock wiring and appearance of a VR. I don't.
Click to expand...

On mine I just cut the wires going to the amp gauge at the regulator and alt feed and taped them to the harness.
 
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