Brian, I have not hooked up the trailer since before this problem began. In regards to the trailer, I mentioned it because the van has many hours and miles on it with the trailer hooked up and I was describing how the charging system used to perform before this current (no pun intended) problem began. Something has changed.
Without the trailer connected, I have tried adding loads one at at time, headlights on - no change. Headlights off, front blower on max - no change. Front blower off, rear blower on max - no change. I can run two of these three accessories with only a slight fluctuation in voltage. when I add the third accessory, with the engine at idle the voltage will drop to 11.7, sometimes lower.
With the a/c on, both blowers at max, headlights on and the engine running at 1500rpm and above, the voltage fluctuates from mid 12's to mid 13's. This is lower than it used to be.
I know that the cable ends are bright and connections are tight. I don't see any corrosion on the wire near the connections. Could one or more of the cables or ground straps be bad? I've checked them with an OHM meter, but I understand that this test can't verify current carrying capacity.
Any suggestions for other tests or possible work around solutions?

 

Your testing and inspecting so far leads me to suspect one or more conductors in the interconnecting wiring harnesses have been affected or acted upon by something, ie: crushed wire. At this stage you seem to have strong and steady output from the alternator as measured at its B+ post which is perfect.

Inspecting the various connector ends was a great step, all too often those can be/are overlooked when a device or component develops issues.

I'd begin checking any and all wiring in the vicinity of the A/C repair---its possible the mechanics unknowingly crushed a wire. Sadly this closer inspection might involve disassembling one or two wire harnesses but with a few commonly available items they can be restored to near factory-new with little trouble.

If you have a procedure or order of adding electrical loads while monitoring alternator output that might be helpful when looking for which wiring harness to more closely inspect.

A bit unrelated perhaps but my SRS system has been affected by my own hand, crushed a few wires feeding the seat belt pre-tensioning devices. The damage is almost unnoticeable but closer inspection (magnifying glass) its easy to see continuity has been affected at the very minimum.

I hope we're being somewhat helpful here---this sorts of issues can absolutely wear a guy's brain out. Worse yet the fix is often so simple we're stunned it escaped us that long.

 

Yes JWA, I do appreciate all of the suggestions offered here. I hope that when this problem is fixed the info here will help someone else!
In regard to the damage that you mention, crushed wires, what did you see with the magnifying glass?
I one of my earlier posts I mentioned the voltage drop test on the cable from the alt. B+ to the fuse box. I would like to know what the maximum voltage drop is for this cable when the system is running under a load. My testing has been done with the headlights on, the a/c on, front and rear blowers on max, and interior lights on.
Also, when I was looking for ground connections to clean, I searched for a ground strap from the engine or transmission to the chassis. I could not find one on my van so I searched online. It looks to me like adding a ground strap from the trans. tail housing to the chassis would be good. There is a ground strap from the chassis to the body.
Any comments or suggestions for other areas that would be good to add a ground?
Thanks for the help!

 

There should be almost no voltage drop at all at your test points, assuming engine running and headlights etc on or running. If its more than 1/10th of a volt there could be an issue.

When making a visual inspection a crushed wire somewhere along the length should be fairly apparent---the wire would be flattened in one or more areas, perhaps the bare wire itself being exposed.

Typically a larger bundle of wiring encased in plastic split loom (which is typically also wrapped in a vinyl no-adhesive tape) won't be affected like this, its those smaller bundles with just a few conductors or several of a smaller gauge. Basically anything that would have deformed any single conductor would be a suspected point.

Adding ground wires from various points as you mention is a good idea----there can't be too many ground points. If you do run additional grounds make sure the component or attachment point does show a ground potential by testing with a continuity tester between the component and the grounding point, ie the frame. If you have positive continuity those connections can be made.

As we've discussed I'd check in the areas most likely accessed by the A/C shop. Its possible there is a small fault with the B+ wire leading to the fuse box---check that termination at the actual box itself, should facing the passenger side, very close to the left side of the radiator. There are two 3/8" locking nuts holding a bus bar in place---its possible that might have developed coincidental problems.

BTW your testing procedure with all high amp draw items engaged is good. If you have time and the patience check one of the tail lamps when the running lights are on---see what voltage you're getting that far away from the alternator and measured through the chassis wiring.

This has to be something simple since you're not having any starting issues etc, drained battery etc.