When I was starting my truck after work today I noticed my headlights dimmed and ammeter below 14 volts where it normally sits when running. It was cold enough for the preheaters to come on and I did not wait until they cycled off before I started the truck when this occured.
It seemed like a a heavy electrical load that came on for about 10 seconds and when it came off, the ammeter went to normal. The same thing happened after the ride home when the engine was fully warmed up.
During the issue, the alternator dipped, but there was no problem light that illuminated on the dash. The second time it happened, I paid more attention and you could hear what again seemed like a heavy electrical load being pulled down, but the preheat light was not on and the truck was running.
It sounds like the grid heater cycling. It should go on and off for several minutes after you start up when called for. I don't know all the parameters that cause them to work, but mine has been doing it also.
Yeah that deffiantly sounds like the grid heater. Its like a blow drying that puts hot air into the intake. It helps the engine run properly during cold starts as well as a faster warm up time. Its perfectly normal for the lights to dim for a minute or two.
Good advice, let the truck warm up a bit before you carry on down the road. I can understand if you don't want to wait 5 minutes, but at least wait for the heater to stop cycling.