I replaced my alternator and belt recently and since then I've noticed a weird voltage issue when I start up the truck first thing in the morning. When I first turn on the key voltage comes up to 12V. As the engine cranks it drops momentarily to 8.5-10V, then when the engine is running voltage returns to about 11.5V. It stays there for 10-15 seconds until then the alternator pulls it up to 14V. Then the voltage (and the engine to a lesser extent) starts surging between 12.5 and 14V. This continues for a couple minutes and then things even out where they should be (about 14.5V).I'm confused!

Completely normal. Heres why http://articles.mopar1973man.com/general-cummins/32-air-system/102-grid-heater

Okay, I figured it had something to do with the grid heaters. I wonder why I never noticed it happening before?

Okay, I figured it had something to do with the grid heaters. I wonder why I never noticed it happening before?

It's normal to be hypersensitive after changing something out.

Totally normal. Grid heaters pull 195 Amps with both elements going and only 95 Amps on a single element. It might be the start temperature is cold er than normal and your seeing even colder temps in the manifold so it using both elements during post heat.

It's normal to be hypersensitive after changing something out.

Yeah, I saw my voltage drop off when the alternator bought the farm, so I was watching it like a hawk after I replaced the brushes. Never really paid that close of attention so must not have noticed it before. I'm sure it had done it before because it wasn't as cold as it had been. I especially liked reading the article from ISX's link-- I ended up reading most of the other articles, too! I'm learning all sorts of neat stuff about my truck!