Question: Alternator Ground Wire

[A1Avette79]

I am having some problems with the battery/starter/alt system. When I stop my 79 (L48, automatic w/air) for a quick stop (like at a gas station) it has a hard time restarting. Starts fine if I make a long stop, say at least an hour. It never grinds as if flooded or vapor lock - just the initial sound of the starter kicking in then silence. Sometimes if I stop for a a little longer it will start but the starter will engage then hesitate for a second - then start up. I had to call my new best friends at AAA 3 times so far. While I was waiting after about 45 minutes I tried the car and it started. I turned it off and tried to restart it but no go. When hooked up to the AAA booster it started immediately with no hesitation. Each time I took my battery (Optima Red Top, a little over a yr old) to the local auto parts store and had it charged up over night. It took a charge and checked out as "good". After being back in the car for about a week (about 5 - 6 starts a day) it would all happen again.
I found a short in the "clock, dome light, cig lighter" circuit. Pulled out the fuse and the short is gone. I put in a new battery thinking that maybe over time the short had killed the battery. I also took the alternator to a alternator shop to have it bench tested - came out good. I called the starter manufacturer (PowerMaster) and the tech said it sounded like sometimes the starter isn't getting enough power from the battery.
I ordered a new set of battery cables which I'll install whenever they arrive. I also wanted to check the grounds in the system. I can see where the battery neg ground attaches to the frame. Where is the alternator ground. I can see the black ground wire from the alternator join up to the wire loom on the firewall. Where does it go from there?

 

[Kevo]

Alternator is grounded by brackets that hold it on engine. You could add one, but should not have to.

 

[GTR1999]

I had that kind of problem with my 69 vette. It was just a crate motor driver with stock starter. A lot of heat is near the starter and soaks in so you may have that problem. You can search online about heat soak issues with solenoid mounted starters. FORD didn't have that issue because it was remote mounted. That has been one resolution for years to convert to a FORD setup but I found the wiring had been repaired at the end by the starter and was loose. I removed the starter and installed a stiffer spring which was an old GM upgrade, then I wrapped it in heat blanket you can buy from Jegs or summit, repaired the wire harness ends and that solved my problem.

 

[LLC5]

I am having some problems with the battery/starter/alt system. When I stop my 79 (L48, automatic w/air) for a quick stop (like at a gas station) it has a hard time restarting. Starts fine if I make a long stop, say at least an hour. It never grinds as if flooded or vapor lock - just the initial sound of the starter kicking in then silence. Sometimes if I stop for a a little longer it will start but the starter will engage then hesitate for a second - then start up. I had to call my new best friends at AAA 3 times so far. While I was waiting after about 45 minutes I tried the car and it started. I turned it off and tried to restart it but no go. When hooked up to the AAA booster it started immediately with no hesitation. Each time I took my battery (Optima Red Top, a little over a yr old) to the local auto parts store and had it charged up over night. It took a charge and checked out as "good". After being back in the car for about a week (about 5 - 6 starts a day) it would all happen again.
I found a short in the "clock, dome light, cig lighter" circuit. Pulled out the fuse and the short is gone. I put in a new battery thinking that maybe over time the short had killed the battery. I also took the alternator to a alternator shop to have it bench tested - came out good. I called the starter manufacturer (PowerMaster) and the tech said it sounded like sometimes the starter isn't getting enough power from the battery.
I ordered a new set of battery cables which I'll install whenever they arrive. I also wanted to check the grounds in the system. I can see where the battery neg ground attaches to the frame. Where is the alternator ground. I can see the black ground wire from the alternator join up to the wire loom on the firewall. Where does it go from there?

The negative cable should go to the engine, which is rubber mounted through the engine and transmission mounts. If the negative cable does not attach to the engine and is attached to the frame, then another heavy ground strap from the frame needs to be attached to the engine. The bottom line is that the battery negative cable needs a good clean tight ground path to the engine somehow, either with a direct connection or through a external frame to engine cable (not a wire, but a heavy 4 gauge or larger cable). The alternator is grounded to the engine through it's mounting points. After installing the new cables check your charging voltage (with a fully charged battery) at the battery cables, it should be 13.5-14.0V at idle and possibly 14.2-14.5V at 2500 rpm's. Let us know what you have. Good luck with it.

 

[Hib Halverson]

Alternator is grounded by brackets that hold it on engine. You could add one, but should not have to.

This is not correct in all cases. Some Corvette harnesses have a black ground wire from the alternator rear end frame to some other grounding point.

The battery grounds to the chassis right under the battery box. Inspect that connection and clean if necessary.

Also, with a car that old you could have corroded battery cables–not the cable ends but the cables themselves, but you have new ones on order so their replacement will correct that issue.

 

[LLC5]

This is not correct in all cases. Some Corvette harnesses have a black ground wire from the alternator rear end frame to some other grounding point.

The battery grounds to the chassis right under the battery box. Inspect that connection and clean if necessary.

Also, with a car that old you could have corroded battery cables–not the cable ends but the cables themselves, but you have new ones on order so their replacement will correct that issue.

The black wire that bolts to the alternator case (usually a 14 gauge wire that would not support 60 plus amps) is not for the charging circuit, it is a source of ground for another circuit that needs one. The ground source for the alternator charging circuit is through the alternator case mounting brackets, engine block, and negative cable back to the battery.

 

[Hib Halverson]

The black wire that bolts to the alternator case (usually a 14 gauge wire that would not support 60 plus amps) is not for the charging circuit, it is a source of ground for another circuit that needs one. The ground source for the alternator charging circuit is through the alternator case mounting brackets, engine block, and negative cable back to the battery.

LLC5 is right and I'm wrong.

After looking at wiring diagrams for several C3s, I see that some C3 alternators have no specific ground wire and others have a 12-ga ground wire bolted to the back of the alternator which grounds parts of the exterior lighting and other items at the front of the car.

Also, some (and perhaps most) C3s do not have a negative battery cable running from the battery to the engine block. They have a short neg. cable from the battery to the frame under the battery and then a short battery cable from the block to the frame right near the passenger side engine mount bracket.

 

[LLC5]

Also, some (and perhaps most) C3s do not have a negative battery cable running from the battery to the engine block. They have a short neg. cable from the battery to the frame under the battery and then a short battery cable from the block to the frame right near the passenger side engine mount bracket.

That's what I was not sure about. If the negative cable on the OP's vehicle does indeed go to the frame and not directly to the engine, then another 4 gauge or larger cable needs to run from the frame and to the engine block for the charging circuit and starter cranking circuit (not to mention all the accessories that are grounded through the engine block).

 

[Hib Halverson]

A number of years ago, I retrofitted my 71 with a neg cable from the battery all the way up to the engine. I have found that starter performance improved.

I suspect that not running all that current through the frame of the car may have other electrical benefits, but I'm not an EE so I'm guessing a bit.

 

[LLC5]

A number of years ago, I retrofitted my 71 with a neg cable from the battery all the way up to the engine. I have found that starter performance improved.

I suspect that not running all that current through the frame of the car may have other electrical benefits, but I'm not an EE so I'm guessing a bit.

That's how I would do it if it were mine, right to the engine block to avoid any possible voltage drop in the future. I would also run a 10 gauge wire (slight over kill probably, but better safe than sorry) to the frame rail for any possible radio suppression and accessories that may be grounded to the frame since the body is fiberglass.

 

[SR'71]

I am having some problems with the battery/starter/alt system. When I stop my 79 (L48, automatic w/air) for a quick stop (like at a gas station) it has a hard time restarting. Starts fine if I make a long stop, say at least an hour. It never grinds as if flooded or vapor lock - just the initial sound of the starter kicking in then silence. Sometimes if I stop for a a little longer it will start but the starter will engage then hesitate for a second - then start up. I had to call my new best friends at AAA 3 times so far. While I was waiting after about 45 minutes I tried the car and it started. I turned it off and tried to restart it but no go. When hooked up to the AAA booster it started immediately with no hesitation. Each time I took my battery (Optima Red Top, a little over a yr old) to the local auto parts store and had it charged up over night. It took a charge and checked out as "good". After being back in the car for about a week (about 5 - 6 starts a day) it would all happen again.
I found a short in the "clock, dome light, cig lighter" circuit. Pulled out the fuse and the short is gone. I put in a new battery thinking that maybe over time the short had killed the battery. I also took the alternator to a alternator shop to have it bench tested - came out good. I called the starter manufacturer (PowerMaster) and the tech said it sounded like sometimes the starter isn't getting enough power from the battery.
I ordered a new set of battery cables which I'll install whenever they arrive. I also wanted to check the grounds in the system. I can see where the battery neg ground attaches to the frame. Where is the alternator ground. I can see the black ground wire from the alternator join up to the wire loom on the firewall. Where does it go from there?

I went thru this a few years ago. Did the battery, alternator ; thinking it was a charging issue. The starter was the problem .

 

[TimAT]

My 69 has a short ground cable from the battery to the frame, and then another short cable from the right frame motor mount stand to the block. Check both of those for a good connection to the frame- and by good, I mean a star washer between the cable end and the frame- on a clean shiny spot. Also cables can corrode internally and the resistance will be higher than a cat's back.
Found one on an airplane a few years ago- 115 volt 3 phase- two of the phases had a current draw of 90 amps. The third one (with the bad cable) was drawing 140 amps. Insulation had split at a junction, gotten wet and presto- lots of corrosion.