fire2nv

Hi, first off i hope this is in the right section, I've got a 1985 full size, 351W 4x4 auto. I've got a charging problem, Seems as tho when i first fire the truck up charges at 14v no problem, Now once i drive for a bit/the truck gets warm the voltage will drop down to 12v or sometimes below at idel, rev the truck up and back up the voltage goes. Now i have had a voltage drop cruising at about 80km/h than moments later it pops back up. So i've replaced the voltage regular (tried more than one), Changed battery's, Had the alternator rebuild (and upped to 60amp) Replaced the belts. So well i'm wondering if there's an wiring harness problem, but anyone else have a wild guess?

thanks !

papa tiger

Check for a blown fusible link wires from the Battery to alternator with a VOM. Black/orange and yellow/black/white.

fire2nv

excellent thanks for the advice papa tiger! Now i know what a fusable link is how ever i've never tested one, should i see any extra resistance threw the link or should it be pretty well straight threw?
thanks

papa tiger

If your reading resistance it is heating up/melting. Heavy current wires don't like resistence and melt/fire results. You can pick up a VOM at Lowes or Home Depot. Remove them and check their resistence. 0 is great. But the needle has to bop over there. If it doesn't it is blown open.

fire2nv

Exellent, thanks! I've got a VOM and my dads actually a matco dealer so i can get my hands on pretty well anything i'll need. My trucks actually in storage for the winter so i'm not able to go out and check it right away so i'll have to get on this, this weekend. Now in theory if a link has been blown wouldn't i lose all charge, not just at idel?

thanks again

papa tiger

Your truck has fuselink wires to alternator/charging circuit, all have to be 100% or it malfs. One energizes the Alt. One goes to a t connection, one goes to battery. If you didn't have a rebuilt alternator I would suspect worn brushes or damaged split ring after testing fusable link wires.

fire2nv

Well i stopped in at my truck on the way home from work and uncovered some wiring to take a look, I appear to have 3 wires coming off the alt, one to the e-choke, one (believe it was yellow) heading to the voltage reg. and another thicker wire which splits into 2, one side appears to head towards the cabin and the other heads to the positive side of the starter relay. the fusable links appear to be on another set of wires heading towards the cabin. Now a bunch of this harness has been hacked and spliced and a few areas of the harness has some corrosion, i'm sort of hoping to head to the junkyard and pull a nice harness and replace the hole darn thing. I've also got electric fans on the truck and i'm wondering if maybe they are taking a draw.

papa tiger

That sounds good.

fire2nv

I've always had it in the back of my head it maybe my aftermarket fans, Well well, Pulled the truck out and into the garage tonight, Ran some cables off the battery and into my multimeter so i could see it in the drivers seat aswell as the gauge in the truck, and sat and let the truck warm, Truck got up to temp, dropped it in gear....nothing...held 13.XX (can't remember exact number but high 13's)......So i went under the hood, Fan isn't on...ok shut it off, check all the power and inputs to the controller, it has power to it but the lights aren't coming on, nor dose it seem to be doing anything. fan's work with direct power. (haven't hooked it direct to the truck and watched the volt gauge yet)...but at this point i'm hoping/looking like the problem is the fan, hopefully its just the controller tomorrow i plan to put a stock fan back on it for the time being and let her run a bit longer

papa tiger

You have to have all the Fusible links good or battery will go dead. Disconnect battery before you try to test them.