As I suspected-you have a Mechanical gauge and not an electric one. Do yourself a huge favor and return it and exchange it for the electric model. Trust me-been there with the CRX and know for sure you do not want the grief involved-there is no way you will properly install a mechanical gauge on a Honda as far as I can tell from my experience.

The location is under the distributor. You will find 2 senders there. One has a 1 wire on it and the other has 2. You want to work with the 1-wire one only.
Not to seem hard-but you should invest in a Helm manual for the car. They are ~$60 from www.helminc.com. If you are uncomfortable with the ordering process online-call them. MY copy has a ton of Post-It marker tabs and we make copies of pages to use in the shop. Better to dirty copies .