1984 Toyota Pickup Charge light and Brake warning light

The Charge warning light and the Brake warning light on the instrument panel flash together at a steady rate similar to the emergency flashers. I can hear what sounds like a relay being activated somewhere under the dash when the lights start flashing off and on. When I start the truck they don't start flashing until the truck has been running for about two minutes. When they start flashing I can turn on any electrical device and they will go out and stay out until I turn off the device. This is the most strange thing I have ever seen this truck do so far. Have you ever heard of anything like this?

Tony