My crossovers recently started shitting the bed and stopped working properly. the woofers would work, but the tweeters went silent. so, i kept all the wiring as it was, and wired the tweeters to the input with an inline capacitor of the same rating as the crossover's tweeter circuit. after doing it to both sides it sounded awesome, until i cranked it up and my head unit stopped playing and went into protect mode. any ideas whats causing it?

 

Were your original x-overs only 6db/oct? Maybe they were not only 12 or 18db/oct but also included a Zobel, making it an easier more stable load to drive for the HU (and now there is none)? Did you apply the capacitors in the correct fashion? They can be directional.
thought- maybe the tweeters were the issue, not the x-overs? Can you try another tweet/driver off the output the the old x-over to see if that works?
Maybe the tweets have a dead short, causing the HU to protect itself.

 

When you disconnect the tweeter from a 2way (or higher) passive network you leave only an inductor as the load across the speaker leads. This is generally bad.