dash gauges and turn signals acting up

Metal gage housing by nature of it being metal, grounds thru the metal screws that hold it in place to the metal dashboard frame which attaches to the metal car body which itself is a ground.

Everything thats metal on the car except for the wiring IS your negative ground. Most if not all vehicles are built this way. Your battery negative may go to the engine block, but theres a ground strap from the engine to the firewall to make the body part of the negative side of the equation. This is because the rubber engine mounts are insulators.

Hope this helps.