Starting issues tach and gas gauge go crazy

Could be several, or even multiple things. I've had similar things happen to mine and so have lots of other people, so here's where I would start. Make sure battery connections are tight and clean. Make sure grounds are tight and clean. Load test the battery. It needs to be in top condition. Mine started and ran the car just fine, but when I put a new battery in all the gauge craziness went away. Scan for trouble codes and pressure test the fuel system. Don't replace parts until you find the problem. On these older cars the scan often points to a certain component but it is actually failing because of poor electrical connections somewhere along the line and it may not be the actual sensor itself. Check through the threads here as well. The subject has been addressed lots of times with an assortment of fuses and wires that have been at fault. Hope there's something useful in all this.