The starting currents on diesel heater are fairly high, I think around 7 - 8 A. Any load like this will suppress the batteries voltage a little. If you have this load on a battery that is increased a little at a time as it is when you switch lights on sequentially you will not notice any dimming of lights. Hitting the battery with a sudden load of 7 A will produce a little dimming but there should be no flicker. Multi voltage LED lamps should not show any change in brightness as the regulators associated with them should provide constant current to the LEDs.
Large changes of light output generally comes from a sick battery or the power to the light and the heater sharing a common wire that is a little on the small size. When you have these conditions you can get funny reactions to heavy changes of load on the battery.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
