Low voltage 3G... Possible improper wiring...

[congerz83]

Doesn't the old harness (below) need to be spliced into the new one?!




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[Broncojunkie]

If you're referring to the 2 thicker black wire coming from the flat spade connector, then those may or may not be used with a 3g swap. Most people run a new heavier gauge cable from the charging lug on the back of the alternator, which looks like was done to yours. So those two can be removed. They may have left them to keep from cutting up the original harness. The cheap way is to cut off the plug, twist the two black wires together and attach them to the lug with a ring connector.

[Broncojunkie]

By the way...that heavy cable attached to your alternator should have a nice big fuse or breaker somewhere inline. Can't tell if yours has one in the pic, but you definitely need one.

[congerz83]

By the way...that heavy cable attached to your alternator should have a nice big fuse or breaker somewhere inline. Can't tell if yours has one in the pic, but you definitely need one.

I have that fuse. I'll take better pictures of my setup. I'm just trying to gather ideas.


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[congerz83]

I re-grounded the pigtail ground. Added two 4g ground wires to the back of the cylinder head. One bolted to sway bar mount the other to the pigtail mounted on the inner fender.

With the vehicle idling @ 1100 RPM... My electric water pump, my auxiliary fans on, hi beams & blower motor on high...


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[1fst86]

There's a couple wires that need spliced in from the original harness. I would check to see if the alternator is actually being 'signaled' to start charging.

[congerz83]

There's a couple wires that need spliced in from the original harness. I would check to see if the alternator is actually being 'signaled' to start charging.

I was told if a new thick lead was installed (with fuse) that I didn't need to splice the old stuff in. If you think otherwise, I'll splice them in right now.

How do I check if it's being signaled?


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[grabbergreen84]

One of the terminals on the alt receives battery voltage, which kicks it on.

[1fst86]

The power wiring to the battery isn't sufficifant enough to carry the voltage. I ran 8 gauge cable for the alt to a circuit breaker, then to the battery. But I did reuse the factory wiring, I just installed a new D-plug, and wired it accordingly.

[congerz83]

I have a 4ga power wire with a fuse


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[Broncojunkie]

If I remember correctly, there should be a wire (white maybe?) ran to a single spade connector on the voltage regulator...back of alternator. If 1fst86 is correct, you may just be running off battery power.

If your alternator is working properly, but not giving you enough charging amps to run all of your accessories, then you should be able to feel excessive heat coming from your alternator. I had my 130a 3g wired correctly, but my fan controller was adjusted incorrectly. The fan was kicking on and running too much. This drew too many amps. As a result, the alternator got so hot I couldn't keep my hand on it.

Run the car again, at idle, with all accessories turned on. If voltage is low, it should be producing power. Let it run 5 or 10 minutes. If it gets hot, that's a good sign you are asking too much of it. If it's cool and still showing low voltage, then it's most likely not charging.

[Broncojunkie]

By the way...do you know how many amps your alternator is rated for? They're not all 130a. I think some are low as 100 (which is still a significant amount better than stock).

[congerz83]

By the way...do you know how many amps your alternator is rated for? They're not all 130a. I think some are low as 100 (which is still a significant amount better than stock).

Mine is a 130 amp. I had a 95 amp in there. When the voltage issues popped up, I replaced it with a 130 amp. Problems continue.


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[congerz83]

If I remember correctly, there should be a wire (white maybe?) ran to a single spade connector on the voltage regulator...back of alternator. If 1fst86 is correct, you may just be running off battery power.

If your alternator is working properly, but not giving you enough charging amps to run all of your accessories, then you should be able to feel excessive heat coming from your alternator. I had my 130a 3g wired correctly, but my fan controller was adjusted incorrectly. The fan was kicking on and running too much. This drew too many amps. As a result, the alternator got so hot I couldn't keep my hand on it.

Run the car again, at idle, with all accessories turned on. If voltage is low, it should be producing power. Let it run 5 or 10 minutes. If it gets hot, that's a good sign you are asking too much of it. If it's cool and still showing low voltage, then it's most likely not charging.

After 10 mins with everything on. Alternator was very hot to the touch.


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[congerz83]

This is negative to the voltage regulator in alternator while the car is running


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[Broncojunkie]

I'd take it off and have it bench tested at the parts store.

[Broncojunkie]

Where did the alternator come from? Was it new or used?

[OldsRocket442]

This is a write up I did a few years ago when I did this in my '79 Bronco. Prior to this one I did one in a '84 Bronco, '76 F100, and my '86 Mustang. The wire colors involved were the same for every one of these installs. I hope this helps.

http://www.fullsizebronco.com/forum/...into-79-a.html

[congerz83]

Where did the alternator come from? Was it new or used?

It was used, but my 95amp alternator was having the exact same issue. That's why I installed the 130amp in the first place


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[grabbergreen84]

If the 130 comes up bad, just rebuild it.

[dynodon64]

Your seeing negative voltage because you have the meter leads hooked up backwards. I see a red lead on the ground wire.

[gmatt]

Your seeing negative voltage because you have the meter leads hooked up backwards. I see a red lead on the ground wire.

Also, set the dial on the multimeter to VDC 20

[congerz83]

I wired the two orange/black wires onto the back with the same result. This thik yellow wire puzzles me. Anybody know what it does?


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[congerz83]

The 95AMP I have has the same problem... I'm clueless at this point

[mustangxtreme]

Your alternator needs to be hooked up like this. I have had mine set up like this for over 60,000 miles.