1972 Chevy C10 350 Charging issue, everything new
 

Hi, I have recently purchased a 1972 chevy c10 with a 350. I knew the owner who put the 350 in about 10 years ago and drove it without any issues. He sold it to a friend who installed Holley Sniper EFI. He mentioned it was having some charging issues before the EFI but rarely drove it and did not trouble shoot the problem. Upon purchase I noticed the volts dropped to 10.6 upon start up. I replaced the alternator with a new 100 amp alternator. Thought the truck was fixed as it instantly showed 14.4v for the first drive after the new alternator. Next drive the truck was showing 12v and not charging appropriately. After more trouble shooting I ended up replacing almost everything in the charging system. New 2 gauge ground wire to engine, new ground wire engine to frame, bypassed voltage regulator and using new ignition hot wire with resistor and inline fuse to internally regulated 100 amp alternator, new 6 gauge alternator hot discharge to starter and existing wire started to battery. The battery is 3 years old but seemed it was constantly being drain and put on battery charger by previous owner. One a few occasion the volts on the EFI digital display would show 14.4 volts, normally after replacing something causing me to think I solved the problem but 95% of the time volts while driving are 11.8-12.3. If I let it idle for a few minutes it will slowly climb to around 13.8 but drop again while driving.

I have checked almost everything that I can think of and gone through the forums multiple times. The ignition hot wire is reading battery voltage and sending power to the alternator. Ive tried using the voltage sensing wire from the old voltage regulator for the number 2 alternator wire and also used a small jumper wire from number 2 to the alternator terminal with the same results. The EFI digital display always shows within .5v of my voltage tester.

What could cause the volts to drop so low while driving and for the charging to be irregular?

I noticed to EFI ground and hot are attached to a stud on the sidewall before going to the battery which I've heard should only go directly to the battery. Planning on fixing this next but also talked to the Holley rep who said that should cause what I am describing.

Any and all suggestions will greatly be appreciated. Thank you in advance.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

If you jumper the EFI directly to the battery what happens?

Re: 1972 Chevy C10 350 Charging issue, everything new
 

Just jumped the hot directly to the battery and no change.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

Start the truck and disconnect battery.
Car stall? If so check wiring and likely change alternator. I had an 1981 C10 when I was younger and bought and received 3 bad remaned alternators in a row! Was nuts. One of them was from NAPA even.
Also Try a different battery to rule it out. Bad cells can cause all kinds of issues.
Mark

Re: 1972 Chevy C10 350 Charging issue, everything new
 

I recently got a bad alternator right out of the box and I purchased that alternator to replace one that had died one week after it went out of warranty. The quality of a lot of parts isn’t what it used to be, but even back in the day you had new parts that were no good. Try charging the battery up and see if it holds a charge. Good luck :gmc2:

Re: 1972 Chevy C10 350 Charging issue, everything new
 

I got 3 alternators (two were warranted) from NAPA before I got a good one. The only problem with my old was that I couldn't get the rotor out of the drive end frame. NB: You can sometimes blow up diodes with the surge, pulling a battery cable while the vehicle is running.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

It sounds like the belt is slipping. That 100 amp alt. pulls a heavy load. If you have a strong fan blade or a locked up fan clutch you are putting a heavy load on the belt. It needs to be real tight. Any oil or glazing can cause it to slip.
George

Re: 1972 Chevy C10 350 Charging issue, everything new
 

You mentioned 100 a alternator i am guessing 12 si has the truck been properly converted to run a si alternator?
Check all your grounds

You could also look at a cs130 conversion

Re: 1972 Chevy C10 350 Charging issue, everything new
 

Thank you for the replies. I have disconnected the battery and the truck continues to run. It is also the second alternator from summit racing. I will try to tighten the belt even though it does feel snug. The belt is older and planning to replace in the future as well.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

You can blow everything electronic including the EFI. I'd never do it.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

Did you convert the wire from the alternator to a #8 wire. If you are still using the stock style feed from the alternator it is grossly undersized.
In the picture it looks like the battery charging wire is too small, it it is connected to the battery not the starter.
The #8 alternator wire has to go to the starter or directly to the battery.
My friend just went through this with an LS3 conversion and a larger wire solved his issues.
You can get a kit to convert it which will include a Mega fuse to protect everything downstream from the battery. I included a picture of the fuse. It doesn't show the covers that come with the fuses.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

I did upgrade the alternator wire to #6 wire with a fuse which goes to the starter and a #6 wire that goes from starter to battery. Next step is to replace the v belts today.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

Attachment 2109501Why did you put in a new ignition hot wire with resistor if this is EFI and not points? I don't think this is related to the charging system but the voltage drop from the resistor in the key on ignition wire could effect the EFI computer.

I second testing a new battree, could be a bad cell. I always buy junkyard alternators instead of rebuilt alternators, it seems that the junkyard ones last longer than the junk rebuilds.

I did a factory HO alternator swap on my truck and used a double pulley from an older 70s ford alternator so I could use double belts to ensure no slippage at high draw. A lot of after market "high output" alternators actually put out less amps at idle then stock alternators but more amps at higher speeds, so with the stock size pulley and with a lot of accessories running (lights, wipers, stereo fans) you can be draining the battree at idle. A smaller pulley will fix that.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

Could be that jumping straight from terminal #2 to alt. battery post is causing the issues.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

I ended up changing the belts and the charging issue was fixed. New belts are tight but still has a squealing noise which I’ll be troubleshooting but very happy to see it charging.

Re: 1972 Chevy C10 350 Charging issue, everything new
 

Using a belt with the same number, but with a X at the end, will carry more HP and run cooler. These are the ones with the notches on the inside of the belt. They kind of look like clog bets but are not.
Glad you got if figured out.