240 having electrical issue need some help please
 

1993 240 sx with sr 20det swap just finished a cam upgrade and head resurfaced and noticed the battery had drained and the warning lights dash stays on. Installed new battery and it started right up and ran great for a day and then started to die when brake was pressed and dash lights would dim. It had an old viper alarm system in it and i thought that might have been causing problem and removed it. The car started right up and has 13.4 volts when running and 12.84when ignition is off. Runs but when u let off emergency brake or depress brake dash acc all dim and temp gauge will max out let off brake and put on e brake and gauge goes back to normal. Switched out tcu with buddies and relays could it be ign switch or something simple checked grounds theres got to be another 240 thats run into this problem please help