Rule #1:
With the ARSC unplugged from the wire harness, check all rails for isolation. Neither reverse section rail, nor any portal rail should be connected to any other rail around them. Don't take this for granted - things happen. Check it properly with an ohm meter, test light, or other device that can sense a short circuit between these rails.

Rule #2:
With a standard two-portal reverse section, only one portal will have power at a time. The other portal is in the detection mode. So, don't ever think you will measure voltage at both portals at the same time - without flipping the reverse section's polarity.

Rule #3:
You can't check polarity of a DCC powered track with a simple AC meter reading across the rails. You can, however 1) check polarity with some tricky AC measurements, or by 2) selecting address zero ("00") on your DCC system and giving it full throttle.

1) Checking polarity of a portal or reverse section with an AC meter can't be done by simply measuring across the rails. But you can check polarity by checking one rail at a time, against a known polarity elsewhere.

If you get a track voltage reading between points A and C, and not between A and F, polarity of the reverse section is set for the other end. In this case, this portal should be in the detection mode - you should NOT get a track voltage reading between A and E, B and D, or even B and E - even though polarity is correct.

The portal at the other end should be a mirror image of this one - with its polarity matching the track going into it.

2) If you select loco address zero ("00") and give it full throttle, one rail will gain more positive power than the other. This allows you to read DC voltage across the tracks.

Checking polarity in this situation is exactly like checking polarity with a conventionally powered DC analog layout.

If you get a positive reading when you place the red probe on A and the black probe on D, and you get a positive reading when you place the red probe on C and the black probe on F, the reverse section is set for this end. This means that you should also get a positive reading when placing the red probe at B and the black at E.

If you get a negative reading when placing the red probe on C and the black probe on F, the reverse section is set for the other end. In this case you should get no (or very little) reading between B and E.

Conclusions:
The key to troubleshooting is knowing how the complete reverse section works. This goes back to Rule #1 at the top. When a portal is powered, the reverse section's polarity should match the portal and the track coming into it.

First determine which portal is powered. If you don't get a reading in either portal, check your wiring. One portal, and only one, should be powered at all times.

Next, be sure that the polarity of the powered portal matches the polarity of the track leading into it.

*If the polarity of the portal doesn't match the track coming into it, reverse the wires going to it. Then, see if the reverse section also matches that polarity

*If the reverse section's polarity doesn't match the powered portal, reverse the wires going to it

**If the polarity of the reverse section matches the portal, but neither matches the track coming into it, you probably have the track power going into the ARSC reversed. Chances are if you reverse these two wires it will fix everything.

There are four correct ways and several wrong ways to wire ARSC. The key is to make sure the portals are the same polarity as the tracks going into them, and that the reverse section polarity matches the portal that is currently powered.

There's more. Here's yet another way figure it out:
Watch to see where the first set of power pickup wheels are when you encounter the short circuit. The following information is so simple, and basic, I'm not even going to tell you what's going on to start with. I want you to stop and think about what's happening, and what conclusion you come to before you read the answers. This way, you stand to learn something about electricity and how to troubleshoot other things.

First Scenario: The loco is entering the reverse section. But as soon as the loco's front wheels touch the portal, it shorts out. Question; what just happened, and why?

Because portal power should ALWAYS match the track going into it, there should NEVER be a short circuit at this point - even when the reverse section is set for the other end. The ONLY answer HAS to be that that the portal is wired backwards.

Does that help you with the second scenario? I gotta warn you here - think outside the box before you come to your conclusion. OK. Here it is.

There can be more than one reason for the short circuit in the second scenario - I told you to "think outside the box!"

The first possibility is probably the one you came up with. Since the portal is wired correctly, there was no short circuit there. But if the reverse section is wired backwards, it will cause a short circuit at that point.

Now, before you continue on, see if you can think of a different reason for the short circuit in scenario #2.

OK, here's another one.

If one of the portal's wires is broken, or has a cold solder joint, it can't detect the fact that a loco is crossing over it. If it can't detect the loco, it doesn't know to switch the reverse section's polarity. And since the polarity in the PORTAL always matches the polarity of the track going into it, even when it's in the detection mode, it won't short out. The short happens when the loco spans the portal and connects the reverse section to the entering track.

Getting the idea of how to think outside the box? See if you can think of yet another reason for the short circuit in scenario #2.

Ready? OK, here's another one.

If you connected the south portal wires to the north portal, and the north portal wires to the south portal, but wired them to match the entering track's polarity, the south portal is telling the reverse section to match the north end, and vice versa.

In reality, this is almost the same as the first answer - in that all you have to do is reverse the wires to the reverse section. This leads us into the finale.

Remember, it was previously stated that there are four correct ways to wire it, and many ways to wire it wrong? Here's the poop.

It doesn't matter which you call north and south as long as you get all the wires connected relative to the one you're calling south.

Call the left portal south, or call the right portal south - it doesn't matter. So, there are two different ways to wire it right there.

Also, left rail / right rail doesn't matter - as long as all connections are made relative to the first wire connected. The instructions say to wire them left, right, right, left, left, right, right, left. It will work just as well if it's wired right, left, left, right, right, left, left, right. Since this can be done with either portal being called south or north, that makes four correct ways.

Lastly, left and right for all connections is in proximity to the first wire connected - it doesn't change at the other end where the polarity changes. When the ARSC connector was designed, this was all taken into account.

Wiring it any other way, besides these four, won't work. Whether you reverse the wires to the reverse section or either portal, or switch the north to south without also switching the reverse section and power input, it's wrong.

Well, that's it. I hope you got your ARSC working correctly. I also hope you've learned something in the process.