Ok, here is some background. I replaced the starter a while back, huge difference. Due to the weak starter, fried the batteries so bought two new batteries. Couple months go by and taking about a 100 mile trip, stopped once, jumped back in and started a little slugglish. Did not think much of it, drove another 50 miles, stopped to fuel up and had a more noticeable sluggish start. Then looked at the volt gauge and read around 9-10 volts. Got to my destination, woke up the next morning and batteries were pretty much dead, started, turned it off, tried again and batteries dead. Put the charger on the batteries, I assume it is the altenator, take it off and head to town. Get it benched tested and they said it was good, so then thought it must be the voltage regulator. Replaced that and still draining the batteries slowly over time. I just noticed that when I cycle the glow plugs, the WTS light stays on for about 8-10 seconds, but immediately after it shuts off, I can hear the selonoid clicking on and off and the WTS light clicks on and off. I replaced that selenoid about a year ago due to starting issues. Any thoughts or suggestions, don't want to keep buying parts I don't need.

 

Glow plugs/relay are working fine. Its supposed to click a few times after starting to help keep the engine running smooth right after startup. If it keeps clicking more than like 30 seconds you'd have a problem though.

It sounds like you have a charging problem. What is the voltage at the batteries while the truck is running? Its possible something else, like a broken wire is keeping the alternator and/or regulator from running correctly.

 

Had plenty of volts at the battery, altenator and cables. My cables are are corroded at the ends. Would that cause a slow drain?

 

the corroded cables won't drain the battery, but may prevent proper charging.

your statement in the first post that you looked at the volt gage (i assume while driving) and saw 9-10 volts tells me that your alternator isn't charging, so i assume that its because the wiring that controls it is bad. did i read that right that you have an external voltage regulator - its fairly common on those to have problems in the wiring between the alternator and its regulator, so check out those wires carefully.
if you don't quickly find the problem, you might count this as a good opportunity to swap to the newer 3g alternator. it'll require some very simple wiring changes, and will put out 130 amps, which is a ton more than your stock unit does.

 

What he said, with a little edit...

Also, the in dash gauge is fairly useless, definitely useless if you crank the fan. Like in my truck it will read something like 10 volts if I crank up the heater/fan to max and have the headlights on. If I stick a voltmeter on the battery it will read 14._something_. The problem there is the smaller gauge wires that bring power into the cab can't handle the load when they get old and oxidized.

People often compare electricity/wiring with water pipes. voltage is similar to pressure, while amps is similar to flowrate. Lets pretend your batteries are like a pressurized 55 gallon tank. To start the truck, you need to turn on a fire hose, so needs pressure, but lots of volume, but only for a few seconds. Now your truck is started, but the barrels are, lets say, 3/4 full. Your alternator kicks in and starts pumping water (voltage) back into your barrels (batteries). Would you rather fill them with a garden hose, or a straw?

Sure you could probably push 30 psi through a straw, but its going to take hours to fill up that barrel. And remember there are also some other hoses draining the barrel while the truck is running (various solenoids and sensors, plus bigger draws like radio, headlights, heater fan). These will drain the barrel fast than the straw can refill it. But a garden hose will make sure work filling it up because it can flow more water (amps) than the straw will.

So your corroded cables are like the straw, and maybe can push 14 volts, but only a few amps and will never recharge the battery.

Now lets step back for a second, sometimes cables will corrode only at the ends, and the rest of the cable is fine. Thats like taking your hose and folding a kink into it right at the end. Now that big pressurized hose only dribbles because it can't get past the kink (corrosion at connection).

Hope this helps you out, and was partly why I said get a multimeter (even a harbor freight cheapy) and it will really help you figure this out. Could also be an issue with the wiring to the external regulator. There is a fusible link in the wire leading from the alternator to battery. If that blows, it won't charge, even if the regulator and alternator work fine. My truck had that issue when the magic smoke came out of the alternator, that sucked the magic smoke out of the regulator and the fusible link at the about the same time.

 

tecgod, i've used a very similar illustration with people, except that i speak in terms of compressed air.

about that magic smoke that came out of your alternator, someone posted a link here awhile back to cans of replacement wire harness smoke made by lucas for british cars. i don't know why, but they tell me it only works on the british cars.... but i like the idea of it as a marketing joke
but on a serious note, even as yours did, one failed part often blows fuses and wires around it. the OP probably has a blown fusible link, or damaged wiring somewhere in there

 

HAHA... I think I've seen that canned magic smoke.

On my truck, one of the diodes in the back of the alternator somehow broke loose and rattled around in the case shorting out. I saw the puff of smoke coming out of the side of the hood and though WTF??? Luckily was only about 2 minutes from home. Swapped out a spare, and no go... Looked up the testing procedure and found voltage at the terminal, then found the crunchy spot on the wire where the fusible link was.

A few months later the voltage regulator blew, I figure it was damaged when the alternator went.

On a side note, I really don't like fusible links. They usually aren't obvious when then blow, and you may not even know they exist on a circuit. Plus unlike a fuse, they aren't a two second fix. My truck has a ****e load of them hanging off the fender solenoid. A second fusebox like the later trucks is a much better solution.

 

and thats exactly why newer cars walked away from this style of fusible link to an easily replaceable fuse which they called a fusible link. any large new circuits i add include a fairly large fuse near the battery end, i usually use the large size found in modern cars, the size thats offered up to 60a, and measure roughly 1 3/4" wide. IMO, it doesn't matter what style of fusible link you use, as long as you have some kind of protection against extreme overloads.