It is the normal trailer wiring convention to have the black wire positive and the white wire negative for the battery connections with the negative circuit tied to ground.
This can be confusing because in modern automotive wiring red is to the battery positive terminal, black is to the negative terminal with the negative circuit tied to ground.
To confuse things further, AC electrical wiring has black the “hot” wire and the white wire is “neutral,” which is tired to ground at the source wiring panel.
Lastly, in electronics, the black wire is for the common circuit, usually ground.
If there is a convenient place near the battery to use a sharpie, write down “White to Batt. Pos. (+)” and “Black to Batt. Neg. (-).”
2015 Wildcat 282 RKX
2011 F350 Lariat, 6.7 L. Diesel, 8 ft., SRW, Reese R20