Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: Would I be able to connect this to RCA out and then wire it to a speaker-level wiring harness in a vehicle?  Wiring harness connects to OEM amp. 2013 Fiat 500.
Document: These adapters simply adapt speaker wire to RCA jacks, they do not step down the signal from line/speaker level to a low level input needed for an amp. If you're looking for an actual line level converter these will not work, your sound will be very distorted. These would only be useful if used to plug into a line level converter that accepts only RCA jacks, you can't use these to go straight from speakers into an amp that needs low level inputs.
Great value, nicely built, I used this for a jeep project installing it on a stereo deck with no built in amp, so I needed to covert the RCA cables to normal speaker wire.
In the description as of right now I am reading on my screen "Rockford Fosgate RFI2SW Adapts High Level Speaker to Low Level RCA Adapter". It may physically after adapting connect speaker wires  into a female RCA socket but electrically it does nothing to adapt from high level to low level. If you want this to give proper signal to an amplifier you have to add a resister to the positive side. Properly used without any modifications this is for a speaker that has a RCA plug as its input.
I used this to replace a bulkier unit which had level adjust and remote output. There was no difference in output quality and if there was it was an improvement. Did the job and saved me space. Just connect directly to the speaker outputs and you're done.
Just got a new receiver and it just had the speaker wire connectors. I tried cutting down some old RCA cable at first but the wire is too thin. Bite the bullet and buy these. They work better, look better, and you won't cut yourself. Ha.
What can I say, I ordered them for my car audio hookup. I was just adding subs to a stock system and these made it a breeze. Simply tapped into the correct wires and connected the RCA's into my amp. Boom. Done. Very simple, very easy. If you are trying to convert your RCA's into speaker wire. Stop. Pick up these and do the setup right.
Converts speaker wires to RCA connections.For use with amplifiers with only RCA inputs and line/high-level input switch (like the Kicker DX400).RCA connectors are not super tight, but they stay in place.
used them to connect a subwoofer to an older reciever and the adapters worked fine. I would use them again.
These adapters are awesome. Saved extra time on an install in a Ford Taurus, because I didn't have to run 3 sets of RCA's, Just utilized the 20 foot long aftermarket wiring harness for a Taurus, since the stock radio is in the trunk.
I purchased these converters so I could wire in an Infinity Basslink in my 07 Honda Civic SI. I tapped off of the rear speaker leads (not the factory sub woofer) and they work great. No whining noise and clean sound. They were a little confusing at first to wire up, I had to go to Rockford's website to get the instructions a little more clear, but in the end I figured it out. Two of the leads need to be connected and grounded to the vehicle.
Answer: No it works as a highs to lows adapter for a after market amp.. A crossover with high to lows would be better