[Timmay!]

aalong,
1. Get rid of the aftermarket tach unless you know all it's specs and hookups and you're sure it's totally compatible.
2. The radio install could have messed up things. Check that area out carefully.
3. Check your grounds under the dash. There's a "crown" of grounds on the left side.
4. Brown is usually ground, but the gauge light bulbs are usually powered by a gray/blue wire, which is daisy-chained. The ground is also daisy-chained.
5. The early 944 wiring diagrams (actually current flow diagrams, SUCK). Here's the trick! Go to the later models section of the diagrams and find the 924S model. It's the same early chassis as the early 944's but in the easier to use format of a real wiring diagram.

The headlights thing is scary. Next, you'll see a smoke cloud from under the dash! Your headlight switch might already have damaged wiring. Check your headlight motor for easy, smooth operation. Headlight motor relay not corroded? Check and clean the major chassis grounding points on both of the longitudinals right behind the headlights. Remember, you're in New York -corrosion.