The only problem here is that you will still need to wire that unit up for use as a fully functioning 7-Pin connector, or else why bother at all if you're only using the "flat four" connector part, which you already have? If you want all 7 pins hooked up, which BTW will also give you 12 VDC for your interior loads, (also including battery
charging and trailer interior lighting,) then you are in for a little bit of wiring under the tow vehicle to make it fully usable. The four flat connector merely taps into the Stop/Turn/Running lights. The 7-Pin gives you more circuits, such as ones you would need to power things like electric brakes
, a battery
charging circuit, (fed from the tow vehicle,) reverse lights, etc. It's all dependent on your trailers needs. If it's just a utility trailer to go to the dump with, then a 4-Pin is all you need. If you have a travel trailer, then you'll need the larger connector to accommodate all the other trailer electrical
loads. Also, depending on your tow vehicle, especially with many European and Asian models, you may also need to add a lighting wire converter to make your lights work properly.
And FWIW, I wouldn't buy one of those K-Mart cheapo units because they aren't made very well, and the wiring they use is generally smaller as well. You get what you pay for. Buy a brand name.