Mine will do it about 4 or 5 cycles when its cold out. I notice it more when dark and the lights are on...

 

Its not an instant ON/OFF, but when the grids cycle, you'll clearly see the volt gauge needle drop to the edge of the normal range, where it will sit for a few seconds or so until the grids turn off and then the needle will slowly climb back up. Then depending on the ambient temp outside, it will repeat in approximately 5-10 seconds. When its dark out and you have the headlights on, its enough of a draw to notice an obvious difference in headlight brightness. When the truck speed reaches 17-20 mph, the grids will stop cycling.

 

I'm pretty sure that after the engine is running only one grid heater will come on.

 

That is a good point, I have about a half mile trip down a 20MPH street before I hit the main road and try not to pass 1200 RPM or so when on a cold start and then the cycling stops, or I quit noticing it...

 

Actually when you maintain around 1100-1200 RPM, the grids will remain on until the RPM's increase or drop back down to idle. Not sure why but its handy when you want to warm the engine with the stick against the fuel pedal high idle.

 

I used to do that stick trick, I would move the seat fwd till it hit about 1200. It seemed as it warmed up the rpm's dropped off a little.

 

A problem I had was the grids were coming on intermittently any time you hit a bump or just out of the blue. I tried wiggling the relays and found if I bumped them just right they would click on. I figured out the low voltage connections were loose on the relays and the plugs were slightly corroded. Cleaned up the boot plugs, slight crimp and pushed back onto the relays. Not a problem since.

 

Thanks for the tip lil dog,I'll definitely give that a try.

 

Exact problem I had. And probably the most relief I've ever had fixing something.