adding 2 gauges

ok - so triple gauges went in ok and all is working though I do have an electrical glitch - I have the radio hot and ground feeding the temp gauge and voltmeter. For the illumination lamps for the 3 gauges, I tapped into what had been used previously to power the illumination lamp for the existing oil pressure lamp. This is on headight switch circuit that dims/shuts off the dash lamps. When I turn on headlights the gauges are all still good as long as I have the headlight switch rotated all the way the the right to shut off the dash lights- if I turn them full on by rotating the switch to the left, the temperature gauge gets pegged to the extreme right position and the voltmeter drops to the 0 volts position. I'm guessing the power required by all that is on this dash lamp circuit when put in the full on position does not leave enough for the temp and volt gauges to function properly......... I suppose I need to find another hot source that will have sufficient amperage in it? anyone's thoughts here appreciated - So daytime it's no issue, but though it's usable as is, I would like to have dash illuminated at night and still have gauges operating accurately....