I use "Southern India" to refer to the southern half of modern India and Sri Lanka. For most of its history, this region has been largely free from large scale invasions and movements of populations. Thus, if you had ancestors there in 1900, you probably could find most of them there in 1. Nevertheless, because it has shared Hindu culture with regions to the north, there has been constant traffic in goods and genes. Your physical features may be the best indicator. People from Southern India and Sri Lanka tend to have darker skin than people from farther north, who have been swamped many times by external invasions. If you are anomolously light-skinned, you may have ancestors from outside of this region.
A couple of major exceptions:
Throughout the study period, there has been maritime trade between Western India, Iran, Arabia, and the Horn of Africa, and East India, Sri Lanka, and Southeast Asia, particularly Malaysia and Indonesia. Indeed, the Jewish community of Southern India dates from the beginning of the study period. Thus, although it's hard to prove, if your ancestors were in a coastal region of South India in 1000 CE, it's not crazy to think that their ancestors could have come from anywhere on the rim of the Indian ocean in 1 CE.
1510 - The Portuguese founded the colony of Goa on the west coast south of Bombay, between Maharashtra and Karnataka. This colony persisted until the 20th century. If your ancestors were in this area in 1800 CE, there's a decent chance that in 1490 you had ancestors in Portugal, especially if your features are anomolously Western European looking. If you are of Indian extraction and have a Portuguese surname, like Indian defense minister George Fernandes, you don't have to wonder.
1504 -1750s - The North Indian/Afghanistan based Mughal Empire gradually engulfed much of South India. During this time, there would have been in influx of northern genes. Thus, if your ancestors in 1800 CE lived in a region that had been ruled by the Mughals, their ancestors in 1490 could have lived anywhere in the Mughal Empire.
1610 - 1948. The British gradually enlarged their influence in India, first through trade agreements with the proxy British East India Company, then directly through the crown after 1858. Throughout this interval, British people (English, Scottish, Irish, Welsh) lived and worked in India. Although there was not widespread intermarriage, there were doubtless plenty of sneaky exchanges of genes. If your ancestors lived anywhere in the British Raj in 1900, then you could have had ancestors in the British Isles in 1800 or 1490. Consider this especially if your features are uncharacteristically Western-European looking.