I have a 99 CTD and want to remove my alternator to have it checked and can't find where the belt tensioner is. I have not fully investigated but figured I would post on here to make it faster. The last week the truck fires up but will not charge above 10 and the check guage comes on when it drops between 8 and 10 so I figured time to get it checked. It has over 200,000 on it and guessing it is the original.

Thanks for the help

Hutch

 

You get to the belt tensioned from under the truck; it's on the passenger side of the front of the engine.

All you need is a 1/2" drive breaker bar to release it. They is a 1/2" cutout for the breaker in the tensioner.

Pull it toward the passenger side and it'll release.

You can see it in this picture, right below the alternator. This is from a truck that we were swapping the cam on....

 

I also wanted to point out that it is easier if you have help... Have a buddy stop by and have the fridge stocked up and COLD drinks ready for consumption.. It does make it easy to reinstall the new belt....
One thing I would do first is check all power and ground wires. See if any are loose. Check the power output at that back of the alt also

 

I just changed the belt on my 98.5. It is a 3/8 drive not a 1/2 drive. I used a 1/2" breaker bar with a 1/2 to 3/8 adapter because the bar was longer. You can do it from the top of the engine. Lower the breaker bar down between the radiator and the alternator. The tensioner is just under the alternator. Put the 3/8 drive into the square hole in the tensioner. Then release the tension by turning the breaker bar to the right. Lift the belt off the alternator pulley. Tuck the belt below the alternator to keep it out of your way and remove the alternator. Reverse the procedure to replace. Check the belt for cracking and wear. Replace if it shows any wear at all. There should be a diagram for the belt routing on a sticker in the front left side of the Radiator support.

 

Oh ya I almost forgot. You don't need help, so drink all the beer yourself.