90 240SX ACC PROBLEM

[drivinsidewayzkouki]

Hi my cousins 240 took a **** its a 90 5spd with the ka24de swap and a viper remote start so heres whats wrong the car starts and runs and while its running if you try to put the headlights on the rpms drop to 500 and then dies unless you turn the lights off only happens with the headlights but the parklights come on fine ive check all the fuses and they all seem ok when you start it the egi relays clips fast for 30 seconds and stops and the radio comes on and off so i switched the egi relay with another relay next to it and it doesnt click the only other things that ave been done where he changed the alternator and relay if any would can help would be great