Electrical Issues?
 

Hello, I have a 97 5.9 Dodge Cummins 5-spd manual 4 wheel drive. The last couple of days my truck has has problems with the check engine, gen, wait to start, water in fuel, and cruise control light all flashing while the tachometer and speedometer both go up and down rapidly unless I am accelerating. While the gauges all flash the alternator gauge also goes up and down between the first white notch and the 14. At night the headlights and all other lights go brighter when I rev the engine and go dim again when the revs go down. The week before this the alternator gauge sat in between the first white line and the 14 without all the other gauges flashing. Could this be a bad ground or bad alternator? I have been unable to find any solutions online so any help would be appreciated, Thanks.

That wold be the first 2 things I would check, Look for bad grounds, and make sure your alternator is putting out the right volts. Also might be a bad Battery... Batts not holding a high enough load. So its drawing power directly off the Alternator. Check your batt terminals, is there any corrosion. Are they tight enough, you shouldn't be able to move the terminals on the post.

Do you have a multi-meter?
If so, Check your voltages. also do a resistance check on your connections.
Start with the negative. Go from the Battery Post, to the Battery Clamp, should be 0 Resistance. then go from the battery, to the engine block, alternator etc. good way to test for bad grounds. if you see resistance == Bad connection.