So, There I was cleaning the battery cables…..

[Kirk]

How do I figure out which is which and get it hooked up correctly?

The use of a multimeter will help a great deal but you may also need to trace the wires to see what they connect to.

The only things that have power are the microwave and USB charging receptacles.

The reason that those have power is that they use 120V-ac power from your shore power cable or an onboard generator. There should also be power to the outlets and to the 120V/12V converter.

The house battery shows 4V, which is a dead battery.

Since you seem to have reversed the polarity, at least to some things, you will be fortunate if it was that low before your mishap. Had the battery been fully charged and connected reversed, it likely would have been far worse.

I’m guessing in my outstanding cleaning methods I had the cables crossed and drained the battery?

That wouldn't have helped the battery and if it was charged to a usable level (10V+) when you hooked things up, then very likely the battery is now bad and probably some other things were damaged. I would have expected that you would have seen sparks when you put the cables back if the battery was not nearly empty. In In my electrical service career, I have seen the result of reversed polarity several times and they were never good. It may be that the main negative cable and the main positive cable were in the proper locations and that seems likely. If so, the damage done could be minimal, but there isn't enough information to be sure. There should be two much larger cables to each post and usually the negative one is black and the positive one red. Do you know that those two were proper? The negative cable when lifted from the battery should measure very nearly 0 ohms to chassis ground. The positive one typically goes to the 12V fuse panel.

 

[Kirk]

Ok so now I have the house battery disconnected, but shore power is hooked up and the master power switch won’t activate.
Does the rig need a house battery to activate the master power switch, even with shore power on?

It would be unusual if your converter requires a battery to be in place for it to supply 12V power to the lights and appliances. Pretty much all RVs in the past 20 years or so are designed to be able to remove the battery and still get 12V power via the converter. If you reversed a lead that goes to the converter, there is probably a reverse polarity fuse on it that you caused to open and that would prevent any 12V power to anything. That is what I would check first. What is the make and model of your converter? Also, is your converter one that is an integral part of the electrical distribution panel with both 12V fuses and 120V circuit breakers? With the make/model of the distribution panel we can probably tell you more and may be able to find service information. A picture of that panel could be helpful.

 

[bigbAZ]

In the electrical trade when taking connections apart in a confusing box we break out the rolls of colored tape and mark everything. If there are a lot of connections we break out the number labels.

 

[John From Detroit]

How to figure out

You will need a good sise 12 volt lamp thew make 100 watt edison based (Standard lamp bulb) in 12 volt along with a socket and some leads. They make 12 volt Incandescent trouble lamp/drop cords . . or they did,

finding a ground ..Hopefully you can trace one wire to the frame but if you can not. Use a jumper cable (standard jump start will work) between battery NEGITINE (-) terminal and frame.

Test. Hook one lead from lamp to POSITIVE Touch other to frame Bright light good.

Now touch that second lead to each wire. Ground Negative) will give you bright light Have inside lights turned on If they light that is a positive lead. You may not ID all this way (You had 2 negatives) If this is a trailer one may be from the tow plug Use a multi meter on OHMS to find it.

Note instead of a 100 watt lamp you can use a smaller one.

Once you ID the negative leads. the rest are easy

The light prevents a direct short

 

[krazeehorse]

Red nail polish is another good marker when you get it figured out. Paint those wires.

 

[Rene T]

Red nail polish is another good marker when you get it figured out. Paint those wires.

Or buy a roll of red electrical tape

 

[gwinger]

It would be unusual if your converter requires a battery to be in place for it to supply 12V power to the lights and appliances. Pretty much all RVs in the past 20 years or so are designed to be able to remove the battery and still get 12V power via the converter. If you reversed a lead that goes to the converter, there is probably a reverse polarity fuse on it that you caused to open and that would prevent any 12V power to anything. That is what I would check first. What is the make and model of your converter? Also, is your converter one that is an integral part of the electrical distribution panel with both 12V fuses and 120V circuit breakers? With the make/model of the distribution panel we can probably tell you more and may be able to find service information. A picture of that panel could be helpful.

The batteries are not needed, but they do stabilize the voltage coming out of the converter.

 

[zulutron]

Or buy a roll of red electrical tape

Or label the bejeezus out of it . . .

 

[Kirk]

Any news on the problem or update on information?

 

[LampsAW]

This has been great advice and greatly appreciated, thank you everyone. I’m going to take it to local RV repair place next week and see what they can do.

Hopefully it can get fixed without too much pain in the A. And after that…I’m going to paint the positive cables neon BRIGHT RED, gonna need sun glasses.
Thanks!

 

[Kirk]

Much better than paint:

Red Zip Ties​

 

[SpencerPJ]

I bet if you took a picture and posted it we might be able to help. Also, a mobile RV mechanic might be a whole lot less $. Goggle that and your zipcode, read reviews. Good luck.

 

[RayIN]

I have a multi meter so I’ll try that.
Ok so now I have the house battery disconnected, but shore power is hooked up and the master power switch won’t activate.
Does the rig need a house battery to activate the master power switch, even with shore power on?

Ignore below, I just noticed you're taking to an RV repair shop.
The "master power switch" is 12VDC only, alternating current is never connected. The shore power main breaker panel handles all incoming shore power.
Disconnect shore power, this prevents the inverter/charger from functioning and allowing false readings.
Make sure no battery cable at the battery bank is touching the RV metal before testing each cable for continuity, again to prevent false readings.
Positive battery cables should not have continuity to the RV frame. ID positive cables with a red zip-tie as Kirk said, then you know which is which, unmarked is negative cables.

This is like eating a big steak, you only take one small bite at a time, eventually the job is finished. Dwelling on the big steak can be overwhelming.

 

[John From Detroit]

As Is said upthread a test light (Say a 50 or 100 watt 12 volt drop lamp) and a jumper cable.
Jumper battery negative to chassis ground then light between positive and frame.. BRIGHT. GOod. now test each cable. > Bright and stays bright. that's a ground. (The chassis ground) Starts bright but dims and goes out (The converter positive) Lights inside come on (Turn on just one low power lamp) Positive. The converter positive may also be the house positive.

No light now those will take some additional testing. But For example if it's a trailer one may be the lead to the tow vehicle, (or two) or it may be the "Always one" Stuff like the gas dector or steps .(The detector will beep when you hit that line_)

 

[Lou Schneider]

As Is said upthread a test light (Say a 50 or 100 watt 12 volt drop lamp) and a jumper cable.
Jumper battery negative to chassis ground then light between positive and frame.. BRIGHT. GOod. now test each cable. > Bright and stays bright. that's a ground. (The chassis ground) Starts bright but dims and goes out (The converter positive) Lights inside come on (Turn on just one low power lamp) Positive. The converter positive may also be the house positive.

No light now those will take some additional testing. But For example if it's a trailer one may be the lead to the tow vehicle, (or two) or it may be the "Always one" Stuff like the gas dector or steps .(The detector will beep when you hit that line_)

Just to clarify - to test each cable the light stays connected to the battery (+) and the other lead is moved to each cable.

 

[John From Detroit]

Just to clarify - to test each cable the light stays connected to the battery (+) and the other lead is moved to each cable.

The light serves two functions. Indicator and current limiter to prevent a short. Incandescent lamps make real good "self resetting fuse/indicators" in that it takes a bit of current to light em up. How much depends on the lamp a 50-100 watt 12 volt lamp will let an inside lamp come on full but prevent a short.

 

[LampsAW]

I got the issue fixed, not by my genius ability though.

It was 3 blown converter fuses. I took it to a local family run RV repair business. Not only did they fix the problem, but they correctly labeled the positive wires so I don’t do another bone head move like I did.

Thanks everyone for helping out!

 

[ferfer]

Thanks for the letting us know the "fix". The fuses did their job and you got off relatively light. Good outcome and just increased 12V system knowledge.