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Message: [QUOTE="robrike1, post: 1549486, member: 33184"] Hi, I am stumped by a rather odd issue. My 2004 F250 6.0 has a drop in voltage from 13 volts to roughly 11.3 during a cold start warm up. I know this is the glow plugs cycling off and on however it also causes my idle to drop up a d down as it does this. Maybe 400rpm or so. I was thinking the cycling of the glow plugs only lasted 2 minutes on a cold start, say 30 to 40 degrees type cold start. I'll plug it up for a few hours below 35 degrees just to be kind to the engine. Alternator puts out rouggly 13.5 volts to battery at idle. I just replaced both batteries with Walmart group 65 850CCA. Prior to that I was having very low charge if left undriven for 3 or 4 days and voltage drop would go to 10.3 volts when plugs cycled on with engine running. Interior lights dim a lot when plugs are cycling so now wondering if it could be a grounding issue somewhere among the many grounds causing this weird rpm drop and lights dimming. I have also noticed cycling lasting 3 to 5 minutes instead of the 2 minutes I've heard is supposed to happen. I'll clean and check my grounds but could a failing GP relay or controller do something like this and is the 2 minute cycle time set in stone? It rarely goes below 20 degrees here in Eastern part of TN. Everything on truck is stock including the pitiful 110amp alternator. Just wondering if I'm on right track with grounds? Batteries were definently going so replacing them was a bit helpful in that voltage doesn't drop to 10 volts. I have an Edge cts monitor. FICM voltage is always a solid 48 volts even when things drop down with the cycling GP's. I'm thinking about a higher output alternator like a Bosch 140amp. I don't have any crazy high current draw items on the truck. Thanks for any tips or suggestions. I searched for this issue but found nothing saying idle dropped when lights dimmed from the cycling. Robert Sent from my SM-G955U using Tapatalk [/QUOTE]