Latin mottoes tend to be terse and open to several interpretations.
Changing a single letter can drastically alter the reading and the composer of the motto may or may not have been fluent in Latin, so it may well happen that none of the offered translations actually match the original intention.
Mottoes can be hard and in some sense impossible to translate and Google translate struggles with even simple sentences, so don't expect it to give anything sensible for a cryptic input like a motto.
With that out of the way, here are some ways to read it:
- Auxilium is "help", nullum is "no" or "none" or similar, and secundum has several meanings but the most common one is "second". There can also be implied words that are not written out, such as est, "is". Whatever the translation is, it is composed of these elements, and these alone give some sense of what it tries to say even though the words as a mere list do not constitute a translation.
- Reading secundum as sequens (it has meanings close to a participle of sequi as it comes from sequundus), my interpretation would be "no help is following" or more fluently "no help will follow", meaning "we have to manage alone".
- If we read secundum to come from sequi with a passive sense (this is common for even for deponent verbs, but secundus has to some but not full extent detached from sequi), then this means "no help is to be followed" or "we must not follow any help". Perhaps the eventual meaning comes close to the previous one.
- Auxilium can also be interpreted, especially in a military context, as "auxiliary unit". With this I would read the motto as "no auxiliary unit follows" or "no auxiliary unit should be followed" (active or passive version, cf. points 2 and 3).
- As Adam points out in a comment, the official translation seems to be "support second to none". This is indeed a possible reading, more (too) literally "support that follows nothing". This interpretation is fathomable, but I would have expected a dative nulli to go with secundum instead. I think the accusative requires reading secundum more verbally than adjectivally.
- Yet another alternative is to read secundum not as the adjective or numeral but as an adverb or a preposition.
The adverbial reading gives something like "no help is behind" or "no help comes after us".
- If we want to take secundum as a preposition, it should be positioned like one.
If we take quite some liberty and read it as a postposition, it means "after" (in rank, time, or something else) or "according to".
This gives the reading option "help according to nobody" or "nobody things we're helpful".
- If we take the "after in rank" reading of the postposition, we get something like "help second to nothing".
Different interpretations 1–4&6 lead to quite different literal translations, but the message seems to be roughly the same: "We need to manage without help."
The official one, the fifth one, is quite different, and out of the rest only number 8 matches it.
Reading 7 turns it around to be quite negative.
This is what Latin mottoes are like!
Many of these readings are quite charitable and do not constitute good Latin in my opinion.
The most natural readings don't correspond to the official one and no reading strikes me as particularly natural, so I would consider the motto to be ill-composed.