A bad earth can cause the strangest of light displays on the dash and the rear lights exposed as they are behind the bumper are prone to corrosion , just removing the bulbs might give you a clue . When the tow socket corrodes inside it does the same because it hooks into the main wiring loom .
Tore my swb 90 apart trying to find the cause of an abs light and eventually worked out it was the clockspring in the steering wheel had failed .