Originally Posted by Pleiades

Er-1 is an error indicating the output signal from the ECU is not being received by the dash/meter; this is why there is no speedo display and the temperature light is on. By far and away the main cause of this is either a broken, abraded or damaged wire in the loom between dash and ECU, or a furred up connector making poor contact. Check the loom visually first, and if nothing is obvious check continuity with a multimeter.

The brake light issue maybe unconnected, but as both switches don't operate the light it must be either a fuse, broken supply wire, poor connector contact or, the thing to try first - the bulb has gone!

It is however quite plausible that whatever wiring fault/connector issue is causing the Er-1 is in the loom at the same point as the issue with the brake light wiring. For example, if particular part of the loom has worn through one or more circuits maybe affected.