'1994 E350 alternator charging?

The faint YELLOW line is the B+ battery voltage power and sense lead wire. This is the "A" wire connected to BATTERY. Not switched, always hot.

The "S" wire connects to that little terminal APART from the regulator on the rear case of the 3G. Look around the rear edge of the alternator and you will see it. One wire run between the two points.

The "I" connection at the ASI connector at the regulator runs to a light bulb, warning dash light. Into the bulb, out the other terminal and to IGNITION.

If your Voltage regulator IS or WAS colored WHITE stop the music. This is a digital dash version. This needs a different hookup.

Likewise STOP if your rig has a VOLTMETER instead of a warning light. This means NO LIGHT AT ALL not merely if it has a voltmeter along with a warning light. This too, needs a different hookup.

The diagram above is for a GRAY color voltage regulator, and idiot light setup.

Hope this helps

I have a 1994 Hornet E350 RV. The chassis seems to be a 92 And changing the alternator has been no easy task. First the old ASI plug was apparently a 'D333'. It had only the y/w 'test' wire and the g/r 'indicator' wire next to each other. (No stator wire) So I had to use my own crimped connectors. I tried ignoring the second (output) plug. I wired the output to the battery directly with battery cable (including fuses), since the new one is a high output alternator. After I ran the motor there was an apparent cascade reaction that burned the 'indicator' wire after an old three wire connector even after the motor was stopped. I replaced that in similar fashion. The new alternator has not produced a charge since. I have re-partialy-drained the radiator to move the hose that blocks removal and removed the new alternator. I have made a new ASI harness. The individual wires may have just come loose. But after opening the sheathing on the second plug I noticed that the original b/o wires were spliced to much heavier yellow wires that seem to go indirectly to each battery. As well as a yellow/green wire that I have no idea where it goes yet. I wish they didn't bundle all the (maybe 100) wires together. Anyone familiar with this type of RV wiring?

Thanks for the update!
Glad you found your problem.

The 70 and 90 ampere models of alternator for this chassis use an EXTERNAL voltage regulator. The very next year Ford started using the large frame 3G alternator with the voltage regulator integrated with the alternator.

The second generation large frame alternator has two weaknesses. The first is brushes that are too short. There is no remedy for this. The second weakness is the stator wire terminals are CRIMPED onto tiny ring terminals (#4) which in turn are soldered onto the rectifier plate. Those wires (Delta configured with the 90 amp stator) MUST BE SOLDERED TO THE STATOR WIRES or they will fail. The crimped on terminals get so hot it actually anneals the copper stator wires. TRANSPO ELECTRONICS devised a rather pricey rectifier plate that uses #8X32 studs and nuts, but did nothing to address the real source of the problem.

The subsequent 3G, 4G, and 6G alternator models all use SOLDERED connections between stator wires and rectifier plate.

One of the best mods you can do to a motorhome with an older 70-90 amp alternator is to replace it with a 130 amp 3G. The unit is absolutely bolt on, and only a wire harness mod is necessary to adapt the regulator. The early alt charges perhaps 30 amps at dead idle, the 3G charges 70-90 amps at dead idle. And 40 more amperes ultimate potential. The 6303 and A2000XX rear bearings will carry three times the load of the original's 6203, and MNJ671 torrington bearings. Three times the bearing life.

Later 4G, and 6G models use a different bolt mounting pattern and really do not offer any real gain.

On our '84 Ford E350, the regulator went out. Dashboard gauge didn't show discharge. Actually it wasn't showing charge either. Replaced regulator and installed a voltmeter instead. Mentioned this to a friend, the part about the inop gauge. He said:
"Proving once again that Ignorance is Bliss."
OP: Glad it's fixed. Was it in Internally Regulated alternator? Several of us thought that by the time your year was built, it would be. Would not have a separate regulator.

It was the alternator

You don't mention what vintage nor model of rv you have but I thought I'd share with you what I experienced on my 1989 Ford E350 with a 460 engine. I had what appeared to be alternator issues in that the voltmeter showed only about 12v and not much more at any speed. Checked system and found that there is a fuse link in the system and it's located in the area of the battery. Checked it and it was good. Being on the road, I gave up and brought the rv into a Ford dealer which changed the alternator and things appeared better but not good. Upon checking further, turns out the in dash voltmeter was faulty! Who would have thought? I know you mentioned that you tried several meters.

Put a charger on the battery and get it fully charged, then take it to an auto parts store for a load test of the battery, alternator, and the rest of the charging system. It's free.

A heavy discharged battery will keep the voltage down.
Locate to see what type of isolator you have.
If it is a diode based one, disconnect the output to the coach battery(ies). You could have a shorted cell or two.

You may want to take you problem to a professional has a better understanding of you motorhome.

Ford didn't offer a 7.9 engine in an E350.
The voltage regulator is mounted on the back of the alternator.

Richard