If the wagerental ratio in Japanese auto production is lower than the wagerental ratio in U. S. auto production, then:

If the wage/rental ratio in Japanese auto production is lower than the wagerental ratio in U.S. auto production, then:

the labor wage cost when compared with another factor of production (capital or land) in Japan is lower than it is in the U.S.  This implies that Japan, which has labor in abundance compared to the scarcity  of labor in US, should continue auto production with labor, which is in abundance instead of using capital or another production factor, which is scarce and costly.

Explanation:

The Heckscher-Ohlin model proposed an economic model which encourages "countries to export what they can most efficiently and plentifully produce."  

Thus, the model emphasizes the export of goods requiring factors of production that a country has in abundance.  According to the Heckscher-Ohlin model, the wage/rental ratio, is computed with a comparison of the wage of labor to the rental price of either capital or land.