weird acting alternator
 

Hi I need help or suggestions
when i first start up in the morning and let it warm for about 2 minutes the charging usually goes to normal. if i start up and just go the charging doesn't kick in until i hit 30 mph. (my speedometer doesn't start working until i hit 30 mph???)
the next weird thing is after it's warmed up to normal temperature and i shut it off and start up again it won't start charging until the speedometer kicks in at 30 mph. just replaced alternator a short time ago.
Any suggestions? Ivan1955

I think this is related to the intake air heater cycling. The truck will cycle the heater on and off until a) the engine temperature is reached or b) your speed exceeds 30 mph or, i think c) the RPM exceeds 1250-1500 RPM or so. After that the intake air heater turns off. When the heater is On, it draws enough current to where there is no indicated charging going on.

Check for codes, you have other problems.
The alternator is supposed to come on as soon as the engine starts triggered by the crank sensor.
Your speedometer should start working as soon as you start moving.
What year is you truck? Early ones have both crank and cam sensors, later ones have only cam sensors.

later 98 24 valve. I've replaced the crank sensor a couple of times. The tac would quit. The speedometer hasn't worked right for 4 yrs. And now the tps is acting up. Goes into a idle for a few seconds. Has anyone tried repairing one?

You might check the alternator for AC voltage feedback. That could affect your apps and a lot of other things. Also, clean all of your grounds. Battery cables and all of the different ground wires. As for the apps, I don't think you can reliably rebuild them. Check into a Timbo apps. Genos has them. Another possibility is a Wells. I think Autozone has them. They are more expensive, but sound like they shoild be good.

One of the guys on another forum had surging problems with a Timbo on 98 year. He thought the Wells would be better.

On a 98, you have both crank and cam sensors. If you replaced the crank sensor, I'd suggest replacing the cam sensor as well. Have you checked for codes?