Man, I love this car when they first came out. Friend of mine had one with turbo with Lotus suspension/handling. Being 1988 would not surprised me if the AUTOMETER FUEL LEVEL SENDING UNIT is bad, it does not matter if its has only 10k miles because of the year. The car is 21 year old and very seldom any electrical system that sit in the chemicals or petroleum that long will last without developing any corrosion or rust. Keep in mind, being 21 years old car with only 60k miles, is telling me its has been sitting for a long time without being driven. Your Isuzu should have 252k miles if it had been driven 12k per year although it average 2800 miles per year. I have seen a 5 year old gas tank that has been left sitting half empty, it has so much rust and corrosion in the tank you would not believed because of moister. This is a true fact, If better to leave the gas tank completely full or completely empty sitting and will have less chance developing corrosion. First, Check all fuses to make sure you getting power to the gages. The only way to test the unit is to test the unit itself. There is plastic connector on top of the tank you can test by unplugging the connector and using the 12v light tester to see if you getting power from main source. My sense tells me the AUTOMETER FUEL LEVEL SENDING UNIT is bad and need replacing. It will cost you 38 bucks auto parts warehouse.com, very easy to replace. If you have plans to keep that car, I would get your self Hayne's auto repair books for 20buck to keep for the next repair. Great book will teaches you alot about the car and the heart of it. Good luck, hope this help some