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Discussion Starter #1 (Edited)
I worked on a 98 6.5 today.Guy said voltage gauge was low.Batteries are only couple months old.Started the truck and connected voltmeter.Volt readings started at 13.5.voltage was gradually climbing and after a couple of minutes got to as high as 17.4 volts.At first I thought it was the regulator.It ended up being the battery cable spacer.look on the passenger side of truck where the drivers side positive cable connects to the passenger(positive) cable.In between them is a spacer.If this spacer is in bad shape and not making a good connection,replace it right away(pry out with screw driver).A bad connection there will cause over-charging and will eventually destroy your batteries and if the voltage gets high enough probably the electronics of the truck.The parts store I got the new spacer from said it is a common problem with the diesels and some gas models.
 

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17.4? measured on the battery post or elsewhere?
 

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Great tip! The other day I was driving and volt gauge got real low and truck began to act funny. I stopped to have alt. checked and it showed good on pass side but bad on driver side. Trouble was the cable that crosses over fan shroud. Seems all electronics work off the driver side battery and starter and alternator work on passenger side. (Provided the "crossover" cable is bad.)
 

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On the 95 and older I believe only the starter connected directly to the right battery, the rest hooked up to the left one.
 

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Is it normal for the voltage to be pulled down a little with head lights, AC, and blinkers? With all off I get 14+. All on, I get about two graduations of the scale under 14. Blinkers cause some fluctuation. Initial charge to 14+ takes several seconds.

Thanks.
 

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I put a larger size + connection between the batteries, and added a - connection between them as well. Replaced cable to main terminal; acid had wicked the entire length of the cable.
 

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The spacer used on dual battery installations has been a BIG problem since the 5.7D days. I've fixed many problems by cleaning/replacing that spacer. It's soft lead material and invites corrosion. It also conforms to any cable irregularities. It is often misshapen by removing and replacing the cable connection. I try to "line up" the impressions/indentations in the spacer with the raised lugs on the cables each time I clean and/or replace the cable connections. Very important piece to the "Phantom Electrical" problems we've all experienced. It's important to the proper sealing of the cable ends also. My advice is: Clean and tighten carefully and deliberately!
 

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OK, this is confusing to me. Does the spacer play some kind of an active function? does it provide some kind of voltage drop - it is resistive in some way? If it contributes a 3 volt drop at say 10 Amps, then E=I*R means R=E/I=3 volts/10 Amps=.3 ohms?

What say you?

Sincerely,

Rob :)
 
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Discussion Starter #10 (Edited)
OK, this is confusing to me. Does the spacer play some kind of an active function? does it provide some kind of voltage drop - it is resistive in some way?
All this spacer does is provide connection between the two posts.If connection is bad it invites arching and erodes the connection even worse.As Fred482 said part of the problem is from loosening and tightening the terminals.It just wears out.The spacer gets worn because of the grooves in the cable terminal.I replaced this spacer and voltage dropped from 17.4 to 15.5.Everyone who owns a 6.5 or any other gm product with dual batteries should know this info as it is hard to diagnose and can lead to un-needed parts replacement to fix the problem such as alt. and also new batteries and any electronic components fried by too high voltage.Maybe this should be a Sticky.
 

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FAQ linked now.... thanks for your contribution. You win a nice dieselplace consolation prize...two pregant gerbils..... ;)
 

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I inspected the overlapping positive cables and found the copper ring terminals on the cables are pitted, the spacer is dinged up and the 5/16 terminal stud had been replaced by a shoulder bolt with a nut threaded down to the shoulder. The red rubber cable end looks like it has been overheated, probably from localized arcing. I bought a replacement cable from NAPA, which had the proper stud included. But, I can't see how to access the starter terminal for the battery connection to replace it. Any one got a method for that?
 

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I put a larger size + connection between the batteries, and added a - connection between them as well. Replaced cable to main terminal; acid had wicked the entire length of the cable.
Yup, same thing with me. Forever the optimist though I got some Optima Batteries (red top) in the hopes that they draw the crud out the cables. Lesson learned: next new truck's Delco batteries will be pulled and blasted with the shotgun before they get a chance to etch and corrode my engine bay...
 

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what about switching to a top post terminal. worked for me.
 

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You can't hope the Optimas will draw the crud out of them; you have to replace the cables. The guys at napa can make you up sets. The acid will wick the full kength of the cable sometimes.
 

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The Optima's are working great! They are stable and best of all: THEY DON"T LEAK! I think I am coming up on the 2-year mark with them.

Only downside is that the hookups to the cables are a little cramped with the air intake being stock. Luckily its all cheap plastic on the intake so it just pushes the filter into the box a little harder. And new battery bolts helped quite a bit-but not the cheap chikity-china junk they sell at the parts stores -

Best "mod" I have made to the truck - De-Delcoing/Everlasting my batteries...

Thanks for the thought Jspringator on the crud-didn't know if it would work or not - don't know of any Napa stores around me though... A-Line is our best in town in my opinion...
 

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Is the spacer on the passenger side battery nessesary? I went to get a new battery and before I knew it the battery fellow had cut off the terminal and replaced it with a different side terminal without a spacer. He said I didn't need it. The two ends are now mashed together in one terminal. Needless to say I was a aggrivated that he didn't even ask. He did say that if I had a problem that he would replace the cable.
 
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