Power distribution question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Krosati · 07-11-2003, 08:31 AM

My truck has the battery cable running to the starter and a fusible link from the starter to the junction block. Then from the JB to the ignition switch. There is also a wire from the battery positive to the alternator. This wire looks like it was added at some time. If I disconnect this wire from the alternator, I can crank the truck but the ECM does not get any power. I am thinking the wire from the battery is bypassing the charging circuit.

Can someone check there setup and see if the Alternator gets power right from the battery to the alternator or if it gets power from the harness via fusable link or ignition switch and how that is routed?

SicMan · 07-11-2003, 09:31 AM

That might be the wire that's supposed to run down to the starter and attach to the battery wire. (Charging circuit) Someone may have just took a shortcut to the battery that way. And the Alternator does hook to the battery. Some are 3 wire or 2 wire systems I believe depending on the year and model...

Any body else with ideas????

I saw your post below .. Is this the same vehicle??? It's also hard to diagnose problems like this without all the facts. Did you do something else? Or did someone else do it? Sorry to go off on you but like I said problems like this need info and background if the circuits were modified or mixed with other model stuff.

Hope that helps........

ChevyThunder67 · 07-11-2003, 12:51 PM

There should not be a wire directly from the battery to the alternator. I am thinking that the wire from the battery is connected to the field post on the alternator. Which in that case the alternator is staying "excited" all of the time. You do not want the alternator to be excited all of the time. The only time you want want the alternator "excited" is just before the engine starts. That is to create the magnetic field inside the alternator to produce power. I am not exactly sure what happens is the alternator is continuously excited. I don't think it is good for it though. I believe that the field wire comes from the starter solenoid( not real sure ). Well, I told you what I think and I hope it is accurate. If it isn't don't be afraid to let me know........I hope this helps

Westley

Krosati · 07-11-2003, 02:10 PM

Thanks for the response. I am trying to get as much info as possible regarding the truck. I bought it for $800 knowing the alternator didn't work. I wasn't told what steps were taken to try to get it working either. The first thing I did was purchase as set of 88 shop manuals (c/k series, light duty trucks, emmisions supplimental,c/k series supplimental, and 1988 wiring diagrams).
The diagrams didn't help as I know the truck is part of the R/V series but the alternator is like those of the C/K series (CS130) and the wiring is different for the R/V series. I want to hook it up like the C/K diagram but don't want to fry the ECM or the alternator.
I have never messed with a post 79 vehicle before so it's all new to me.
All I have done so far is try to track down any breaks in the wiring since I installed another alternator that was tested in the shop. I recharged the battery (slow trickle overnight) Battery reads 12.8 volts even with the alternator running. I know its not charging so I figured the Charging curcuit is bypassed somewhere so the alternator is not "excited"
Any suggestions.
I hate to repost the same topic over and over but sometimes folks get a better idea of what is being asked if asked a different way.
I appreciate any and all help .

Krosati · 07-13-2003, 01:13 PM

Just an update on my alternator troubles.
Since not being able to find the source of the trouble, I decided to modify the alternator to make it self exciting. My local alternator shop suggested it and installed the part in less than half an hour. Cost me less than $50 and now the burb is charging great.
I appreciate the help you guys have offered and I hope I can return the favor soon.

07-11-2003, 08:31 AM	#1
Krosati Registered User Join Date: Jul 2003 Location: Texas Posts: 49	Power distribution question My truck has the battery cable running to the starter and a fusible link from the starter to the junction block. Then from the JB to the ignition switch. There is also a wire from the battery positive to the alternator. This wire looks like it was added at some time. If I disconnect this wire from the alternator, I can crank the truck but the ECM does not get any power. I am thinking the wire from the battery is bypassing the charging circuit. Can someone check there setup and see if the Alternator gets power right from the battery to the alternator or if it gets power from the harness via fusable link or ignition switch and how that is routed?

07-11-2003, 09:31 AM	#2
SicMan Alledged Sick Person Join Date: Apr 2003 Location: Wolcott, CT. Posts: 88	wire That might be the wire that's supposed to run down to the starter and attach to the battery wire. (Charging circuit) Someone may have just took a shortcut to the battery that way. And the Alternator does hook to the battery. Some are 3 wire or 2 wire systems I believe depending on the year and model... Any body else with ideas???? I saw your post below .. Is this the same vehicle??? It's also hard to diagnose problems like this without all the facts. Did you do something else? Or did someone else do it? Sorry to go off on you but like I said problems like this need info and background if the circuits were modified or mixed with other model stuff. Hope that helps........ __________________ You lock the door, and throw away the key .... and there's someone in my head but it's not me! Last edited by SicMan; 07-11-2003 at 09:43 AM.

07-11-2003, 12:51 PM	#3
ChevyThunder67 Registered User Join Date: Jun 2003 Location: Las Vegas, NV Posts: 12	There should not be a wire directly from the battery to the alternator. I am thinking that the wire from the battery is connected to the field post on the alternator. Which in that case the alternator is staying "excited" all of the time. You do not want the alternator to be excited all of the time. The only time you want want the alternator "excited" is just before the engine starts. That is to create the magnetic field inside the alternator to produce power. I am not exactly sure what happens is the alternator is continuously excited. I don't think it is good for it though. I believe that the field wire comes from the starter solenoid( not real sure ). Well, I told you what I think and I hope it is accurate. If it isn't don't be afraid to let me know........I hope this helps Westley __________________ 2000 Dodge 2500 diesel 1992 Jeep Cherokee 1976 Chevy K20 smallblock 1967 Chevy C10 smallblock 1974 Chevy Nova 2dr.

07-11-2003, 02:10 PM	#4
Krosati Registered User Join Date: Jul 2003 Location: Texas Posts: 49	Thanks for the response. I am trying to get as much info as possible regarding the truck. I bought it for $800 knowing the alternator didn't work. I wasn't told what steps were taken to try to get it working either. The first thing I did was purchase as set of 88 shop manuals (c/k series, light duty trucks, emmisions supplimental,c/k series supplimental, and 1988 wiring diagrams). The diagrams didn't help as I know the truck is part of the R/V series but the alternator is like those of the C/K series (CS130) and the wiring is different for the R/V series. I want to hook it up like the C/K diagram but don't want to fry the ECM or the alternator. I have never messed with a post 79 vehicle before so it's all new to me. All I have done so far is try to track down any breaks in the wiring since I installed another alternator that was tested in the shop. I recharged the battery (slow trickle overnight) Battery reads 12.8 volts even with the alternator running. I know its not charging so I figured the Charging curcuit is bypassed somewhere so the alternator is not "excited" Any suggestions. I hate to repost the same topic over and over but sometimes folks get a better idea of what is being asked if asked a different way. I appreciate any and all help .

07-13-2003, 01:13 PM	#5
Krosati Registered User Join Date: Jul 2003 Location: Texas Posts: 49	Just an update on my alternator troubles. Since not being able to find the source of the trouble, I decided to modify the alternator to make it self exciting. My local alternator shop suggested it and installed the part in less than half an hour. Cost me less than $50 and now the burb is charging great. I appreciate the help you guys have offered and I hope I can return the favor soon.



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