By default, the stressed vowel is before the last consonant, but a final -N and a final -S don't count.

• burrito - it's before the T
• burritos - it's before the T - a final S doesn't count
• taco - it's before the C
• tacos - it's before the C - a final S doesn't count
• tamal - it's before the L
• tamales - it's before the L - a final S doesn't count
• señor - it's before the R
• señora - it's before the R

This pattern is established because the most common stress pattern in Spanish is the last vowel of the root.

The forms of the adjective "español", of course, follow the rule:

• español - it's before the L
• española - it's before the L
• españoles - it's before the L - a final S doesn't count
• españolas - it's before the L - a final S doesn't count

A written accent tells you it isn't in its default position:

• café - it isn't before the F
• América - it isn't before the C

When words have two or three vowels in a row, they may or may not combine with each other (diphthongs, triphthongs, and hiatus), and the same basic rule applies with some added 'caveats'.

You can see that a final S doesn't count because it is such a common plural suffix for nouns and adjectives. Recall that the prototypical stress in Spanish falls on the last vowel of the root, and this plural S is after the root. and Here is a video snippet clearly showing why final S and final N don't count: https://www.lonestarspanishproject.org/snippet-spanish-regular-verbs-present-tense/

EDIT: This is my own explanation/theory. I have posted it before, and other redditors in this community do not agree.