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“Just Put a Switch In That Wire”

Posted By ScottM Last Year
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Freightrain
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Just chased down a short in a friends car. Started with test light in series with ground cable on battery. Start unplugging things until the light went out. It was the voltage regulator on the alternator. It would kill a battery in a day just suddenly while parked, but would charge okay while running.

Larry

I'm no expert, but I did stay at a Holiday Inn Express last night.
ScottM
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I will just pull it put and see what happens, and then see what I have for power following that to try and get lights to work and the motor to crank. On one level I am looking forward to ripping all of the junk and broken wires out and cleaning up the harness (there is a lot of un plugged connectors and other random things just hanging around).

======================
www.cachecreektruckshow.org

Scott McKenzie
- 1950 Bullmoose B624 forklift
- 1964 Pacific SRDD-D - http://prograph.smugmug.com/1964-Pacific
- 1973 Pacific P9
- 1980 Chevy C60
- 1983 GMC 2500
www.pacifictruckclub.org
www.hayestruckclub.org


wayne graham
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You are correct Geoff but I have found a lot of problems to be the ground. Always the first place I go.

I cried because I had no shoes till I met a man who had no class.
Geoff Weeks
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My guess is there is a fuseable link that is burned or removed. They are back feeding the power somehow. Like I said earlyer, your going to have peel away the fixes and solve the problems one by one.  Chassie should be the neg side of the battery and when you check for power check between what you are testing and ground. (chassie). 
 I never been lucky enough for it to be only one problem and one thing fixes everything. It is most often layers on layers of problem and shade tree fixes. The good new is once you peel it back and fix the original problem correctly everything works at is should. It will take time and sleuthing to sort it all out.
Eddy Lucast
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Anytime electrical systems don't make sense. I start cleaning or recreating grounds.
Then I'm ever more confused, LOL I hate electrical problem.

Double Mountain Manufacturing LLC
Eddy.Lucast@remotedata.com
203-228-1961

ScottM
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I will have to start by disconnecting the alternator after running through the checks here - once I get the battery charged. The truck has sat for a week in the shop and is completely dead this afternoon. I took a closer look at the wiring which is nothing short of a nightmare. His switch is installed so that it interrupts power from the ignition stud on the terminal block to the engine overspeed terminal - it is like a jumper between those terminals. I could see how that would kill the motor when the switch is flicked off but it makes no sense to me why no lights or any electrical will work without that switch being turned on.

I put a volt meter across the terminals of the switch, when the switch is off I see 10.18V (battery low / dead) across the switch terminals, if I turn the switch on I see milivolts across the switch and my lights will come on. I am totally confused, my key switch is in the on position when testing. If I turn off the key and turn off this goofy switch my lights go out and I still have 10V across the terminals of the switch.

If I pull this switch out I will lose the connection between the ignition terminal block stud and the engine overspeed terminal on the firewall. But the truck will be totally dead so I am missing a connection somewhere between these two terminals and the key - my thought is between engine overspeed and key on but I have no idea.

I have ordered the wiring diagrams and am hoping they will help sort this out but while I wait await their arrival I am open to any hints. Bandaid fixes drive me nuts. It would have taken half the time to do this properly and install a night switch.

======================
www.cachecreektruckshow.org

Scott McKenzie
- 1950 Bullmoose B624 forklift
- 1964 Pacific SRDD-D - http://prograph.smugmug.com/1964-Pacific
- 1973 Pacific P9
- 1980 Chevy C60
- 1983 GMC 2500
www.pacifictruckclub.org
www.hayestruckclub.org


doubleclutchinweasel
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Had a bad diode in the alternator on the wife's Mustang.  Same thing.  Would kill the batter overnight.  Also, voltage read a little lower than normal on the gauge while running.
Unhooking the alternator overnight verified the issue was in the internal regulator.  When it was unhooked, the battery would not drain overnight.
As with most electrical issues, sometimes it helps to disconnect and reconnect things and see when/if the problem comes and goes.


Eagles may soar, but weasels don't get sucked into jet engines.

Geoff Weeks
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Depends on how it is wired. Most likely it would have the little "white" triangle shaped internal reg, with a 3 wire system. 
 That is connected to the stator on the A/C side. It can be wired in many ways, with one of the external connection made right to the output stud, or  not, that is the "sense" connection. There is another which turn the regulator on when the ign is switched on.
 Conversely it could be a "one wire" alternator, in which case,  Both the sense, and turn on are controlled by the A/C side of ouput diodes. (via a diode trio)  But there is no voltage on the a/c side of things when the alternator is at rest. 
 I think I have had only a very small handful of alternator failures that can be traced to main diodes shorting, but it can happen.
If it has a Gray Ghost  (Delco 25 or 26 SI) it uses a mica insulator between the positive diode plate and the case, I have seen when the gasketing has failed, where moisture will cause corrosion in the area that will conduct. Easy to fix
 Easy test to see if the field is energized when the system is stationary, hold a key or other thin steel on a ring near to the rear alternator bearing, if it is attracted and held against the case, the field is energized.
Tony Bullard
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Geoff Weeks (11/29/2020)
Hard to say, my guess is he is back-feeding the ign circuit, but I is almost impossible to guess without seeing where the wires go. 
 I often find problems like this are multi-layered. Someone does some back-yard fix to a problem, that causes another problem, to which another half-baked solution is applied,  which causes yet another problem and it goes in layers that to fix, you have to peel back the fixes like a onion skin.
 I would remove the switch and see what problem it causes, then move onto that one.
 A diode failure can cause a battery draw, but it is highly unlikely. Diode failures are far more common to fail open, and not shorted. To cause a draw, it would have to have a positive diode fail shorted. It is most common when a high voltage spike arcs across the component layers in the diode. Removing the battery while the engine is running (esp at speed) can be a cause.


I think what fails are the internal voltage regulator diodes and transistors allowing a small amount of current flowing through the field coils. Not the high power stator diodes.
Edit: just got thinking-- that C60 probably has a external regulator.



Tony
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I would suspect he meant to put in a battery disconnect switch.

Dan Cornett


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