Ok so even tho my alternator tested good and both batteries are new i will drop low on my voltage at idle so im looking at a high output alternator (i do have accesories to have the need for one) my question is im trying to find one under $300 but what upgrades do i need to support it like what size cables etc

 

Did you measure the voltage AFTER the glow plugs cycled off (1-2 minutes)?

Otherwise, a higher output alternator will not magically fix a charging issue that's related to wiring, batteries, etc.

 

Agree with madpogue here... you're going to rip out all of the wiring anyway with a new alternator, so why not start there? I had a similar problem where everything measured good but I was having weak cranking. When I disconnected the cable at the starter the wire terminal had corroded to nothing - hard to pass electricity through rust! - and I had to repair that to fix the issue.

I know that isn't exactly what you're seeing here, but I would triple check the wires before dropping for a new alternator. If you do decide to go that route, maybe look into adding a second alternator, ala the ambulance package?

 

The voltage after the glow plugs cycle is 10-11vdc both batteries are good, but today i unhooked the fan for my trans cooler and it seemed to be ok now

 

No way that fan should draw that much. It's probably smaller than an electric rad fan on a FWD car, and those run all day when the A/C is on. I'd swap that fan motor out.

 

^^^. That is a good thought. You may have a fan issue causing excessive draw.

 

Ok ill look into the fan, but even without the fan after the glow plugs cycle im still under 12vdc i checked for a parasitic draw and didnt have any that was concerning

 

And you're waiting a good two minutes for the GPs? Or at least listening for the relay to de-energize?

 

Have you recently replaced the GPR ? It needs to be ground Isolated . All of the electical connections need to be squeeky clean . Who tested the batteries & the alternator ?

 

Yea i replaced it less then 6 months ago, i will check all of the wires, i have a feeling the wire that goes to the drivers side battery is corroded, that was the battery that went bad, the ground side of the fan is on that battery and that battery was pretty nasty looking compared to the passanger battery

 

If the GPR is the wrong one , it can stay on continuously. ( not ground Isolated )Batteries "should " be replaced in pairs . ( at least on our trucks )

 

How can you tell if its ground isolated?

 

Set your multimeter to either resistance or continuity. With the relay removed from the truck, put one probe on the mounting base, and touch the other probe to each of the small terminals. If the meter shows continuity, or no/low resistance, on either terminal, then it's case-grounded and you should NOT use it.

 

so im looking for an ol reading correct?

 

Yeah, likely anyway. Some meters read OL when used for resistance and there's infinite resistance.