It sounds like you're encountering a situation where accessing the second domain redirects you to the first domain, which is unexpected behavior after setting up WordPress installations on both domains. Here are some steps you can take to troubleshoot and resolve this issue:
### 1. Check WordPress Settings
1. **Verify Site URL and Home URL**:
- Log in to the WordPress admin dashboard of the second domain.
- Go to **Settings > General**.
- Ensure that the "WordPress Address (URL)" and "Site Address (URL)" are correctly set to the second domain's URL (e.g., `http://seconddomain_com`).