Alternator issue

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choll

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Greetings everyone
I am having a charging issues with my blazer. I just replaced the motor and am having issues with the alternator charging. The truck years ago was converted to the rosecommon modification, never had an issue charging. At first I thought a bad alt as I was not getting 14 volts at battery. Pulled the alt and put in one that tested good. Not charging. I get the one I just pulled tested its good. So I put that back in. Im thinking bad ground, change the ground wire. I hook up the ground wire to the post on the far let of the alt, I touch it to the ground on block it sparks, I hold it there for a few seconds and its getting hot. I do a voltage check at the wire and its pushing 2 volts., black wire in pic. I hold it to ground and now Im getting 13.36 volts at battery but wire is getting hot. the connector is clean and the two smaller wires red with black tape and orange are hooked to the post next to the quick connect.
Any ideas any help would be great trying to get this fixed so I can take a road trip from Miami to Nj to see my mother. Everything else works fine.

Chuck
 

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richingalveston

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did you get the ground wires connected to the block. There is a ground wire from the cab and one from the bus bar. maybe these are not connected properly.

You may have a wire shorted out on the block some where and the voltage is coming through the block from the battery/alt output and not actually coming out of the alt ground.
Being that you do not have a stock system, it is going to be difficult to get help here on the forum. You posted it in the right section but without a new wiring diagram of your truck to see what has changed, everyone here will just be guessing.
 

choll

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Thanks for the reply. Nothing at the wiring harness is changed except the resisters on the fire wall were taken out and a jumper wire was put in. the batteries connections changed to make them put out 12 volts hooked in series I think. Nothing else changed. The belt on the drives side and wires were taken off and taped up Worked for ten years its driving me nuts....guess Ill be tracing wires this weekend. We all love to do that LOL
On the attached pic the stud that Im point at should there be voltage there when the key is on
 

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richingalveston

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that is the glow plug relay and yes when the wait light is on then there should be voltage there but when the light goes out it should stop and start to cycle on and off until the engine is up to temp then once up to temp, it should stay off. This cycling is controlled by the glow plug controller card and there is a temp sensor that the glow plug card uses to determine when to stop the cycle.
You should here that solenoid click on and off. it is normally fairly loud.
That is a completely different circuit than the charging circuit and really should have nothing to do with your alternator issue.

That relay should be an isolated ground relay so none of the contacts on the relay should have continuity with the mounting bracket. If it is not an isolated ground relay then it can put voltage to the chassis and to all of the grounding system. check the relay and make sure that all of the terminals are isolated from the mounting bracket/ outer case of the relay.
 

richingalveston

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after looking at the pic again, you should not have that many wires connected to the relay. your 12 volt terminal block is empty, most of those wires should go to the 12 volt terminal block and not the relay. Your jumper from the resistor should go to the terminal block and then to the relay with a piece of fusable link wire. The other wires on the relay should also go to the terminal block ( the block just above the relay). at this time it does not look like the relay and glow plug system is protected by a fusable link.
 

choll

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Got it working thanks.
Can you think of any reason I cant get the alt to charge? I've pulled it 3 times and it bench tests fine. The batteries are new. I am not getting any voltage to the batteries. The gen light in truck is not lighting so I assume its sensing a good alt. Any ideas
 

chevymike

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Does the Gen lights light up when you turn the key on but before you start the engine? If not, that is problem #1 as it needs those light to work for the alts to sense the ignition is on and they should start charging.
 

choll

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The light is not going on, how I missed that who knows. I must have a keen sense of the obvious. LOL What is next that I should look at. I really appreciate your help!
Chuck
 

chevymike

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There will typically be two reasons that light does not go on. One, a serious problem with the alts and they are not getting any ground source from the regulator (not likely but possible) or you have burnt out bulbs/bad connection on back of gauge panel/bad wiring between gauge panel and alt. You are going to need to study the TM wiring diagrams and figure out what wires are what. First thing I would check is the actual bulbs/bulb holders on the back of the dash. Not one of GM's better ideas.
 

choll

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I check the fuse and it was burnt replaced it nothing changed. Going to pull dash apart on Saturday and replace bulb. Any way to buy pass some of the wiring to get the alts to charge batteries
 
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