Alternator Grounding

[Coop8202]

Hello all. 1976 K30. Intermittent starting issues. New battery, newer alternator. Starts perfectly after sitting for weeks, starts consecutively cold and hot. Pulled into gas station, off for 5 minutes or so. Almost like battery was shot, barely cranked. Volts reading below 13V on dash. Checked output from alternator next day, read normal. Volts on dash between 13V-15V, but when using multimeter and doing load test, getting between .7-.9 voltage drop at alternator and alternator bracket. Assuming this may an issue with grounding and not the alternator intermittently charging or starting to go?

 

[Ricko1966]

Hello all. 1976 K30. Intermittent starting issues. New battery, newer alternator. Starts perfectly after sitting for weeks, starts consecutively cold and hot. Pulled into gas station, off for 5 minutes or so. Almost like battery was shot, barely cranked. Volts reading below 13V on dash. Checked output from alternator next day, read normal. Volts on dash between 13V-15V, but when using multimeter and doing load test, getting between .7-.9 voltage drop at alternator and alternator bracket. Assuming this may an issue with grounding and not the alternator intermittently charging or starting to go?

What was your voltage reading driving to the station?Sand and clean your alternator case and mounting bracket. The alternator volt drop itself would not cause your slow crank,unless it had not been charging the battery on the way to your destination. You should keep a multimeter with you so you can check voltage at the battery and
volt drop tests on positive cable and negative cable at time of occurrence. I'd do volt drop test positive and negative cable right now any way. Not to insult you just checking. Do you know what volt drop tests are and how to perform them?

 

[Coop8202]

What was your voltage reading driving to the station?Sand and clean your alternator case and mounting bracket. The alternator volt drop itself would not cause your slow crank,unless it had not been charging the battery on the way to your destination. You should keep a multimeter with you so you can check voltage at the battery and
volt drop tests on positive cable and negative cable at time of occurrence. I'd do volt drop test positive and negative cable right now any way. Not to insult you just checking. Do you know what volt drop tests are and how to perform them?

I had not paid much attention, as I thought the new battery fixed any issues i previously had. I started it first time in 2 weeks, fine. Drove an hour on highway. Parked. Started after about 4 hours of sitting, fine. Drive 20 minutes of backroads to gas station, hardly started. This is when I noticed the volt gauge reading less than 13 once it started back. Headlights were off, I had blower fan on low and radio on the whole trip to and from. Drove about 45 minutes home, no issues starting at all since. Started back to back to back to back, easy. And starts cold fine.

I believe I have a basic idea of what they are. But i am open to any tips or methods on how to perform them. The one I think i did was on the neg battery terminal, and then touching the alternator case and then the alternator mounting bracket. Lights, blower, and radio on. Both tests showed -.7-.9 volts which from my understanding is a big issue since it should read less than -.2-.1 volts. Engine block is painted so it just read 0 volts when i tried to do it there. I can replace the alternator for $200 but if its a bad ground its not going to fix the issue. I just fell like I can't "trust" the truck to start now.

 

[goldpack]

just for asking (spit balling)

is the alternator wire newish?,...are the battery cables newish.?

what is the new alteranator exactly: brand / model # / bought at ?
new / used/ reman ?
(half baked/ half crap / tests fine one minute, pissing you off the next= reman)

 

[Coop8202]

just for asking (spit balling)

is the alternator wire newish?,...are the battery cables newish.?

what is the new alteranator exactly: brand / model # / bought at ?
new / used/ reman ?
(half baked/ half crap / tests fine one minute, pissing you off the next= reman)

Its a resto truck so everything is newer and good condition. Alternator is probably 5-7 years old ish. Duralast (AutoZone) I attached a photo.

 

[goldpack]

reman from a parts store.

....if a new / replacement is in your future:
I would buy a DB electrical one. (maybe with wires).
(offices in Tennessee,..= new and not remans,... no core ).

and I say "if"....

you might check all engine grounds,...with a list. (...and getting to be fall and time for rodents to chew...especially in places you can't see.).

The SquareBody Reference Library

Part #s, RPO Codes, TSB's, Cast #'s, etc

www.gmsquarebody.com

 

[Doppleganger]

That AZ a reman? They (all of them do really) take an alt with 300k on it....the bearing fails so they replace it (blast and clean the housing - new stickers)....but leave the brushes with 300k in it. Cannot tell you how many times I went through this. Pull the regulator and it was worse than the one I just replaced. Local guy's car I was working on - he bought a reman Bosch in 2021.....regulator was "Made in West Germany". lmao

I bought a new Interstate battery last Dec. This past August, we brought groceries back - I was going to unload and then go wash the car. Took everything in, came out - dead as a door nail. Not even a click. Pulled it and took it to NAPA to test. <9V and would not take a charge. Bad cell(s)....that just happened on an 8 month old Interstate.

In this day and age, I wouldn't rule anything out.

 

[Ricko1966]

I had not paid much attention, as I thought the new battery fixed any issues i previously had. I started it first time in 2 weeks, fine. Drove an hour on highway. Parked. Started after about 4 hours of sitting, fine. Drive 20 minutes of backroads to gas station, hardly started. This is when I noticed the volt gauge reading less than 13 once it started back. Headlights were off, I had blower fan on low and radio on the whole trip to and from. Drove about 45 minutes home, no issues starting at all since. Started back to back to back to back, easy. And starts cold fine.

I believe I have a basic idea of what they are. But i am open to any tips or methods on how to perform them. The one I think i did was on the neg battery terminal, and then touching the alternator case and then the alternator mounting bracket. Lights, blower, and radio on. Both tests showed -.7-.9 volts which from my understanding is a big issue since it should read less than -.2-.1 volts. Engine block is painted so it just read 0 volts when i tried to do it there. I can replace the alternator for $200 but if its a bad ground its not going to fix the issue. I just fell like I can't "trust" the truck to start now.

Okay engine running,you touched the negative post with 1 meter lead the alternator case with the other and got a.8 volt reading? If so yes your alternator is not getting a good ground. But the alternator grounds to the engine,so you need to verify the engine is getting a good ground. Same test but battery negative post to bare metal on the engine somewhere. Positive side you go battery post to starter positive post. Notice I keep saying post,not end you can have good voltage to a terminal end,but not be have good voltage to the post. A little short cut for testing positive side, test it engine off check from battery positive to alternator charging post. Have someone crank the starter,If that checks good your battery positive and alternator charging lead are both good.

 

[Coop8202]

So, I haven't had time to perform anymore load tests, but I was able to play around with the negative battery cable. It runs directly from the battery post to the passenger side frame rail. Setting the multimeter to ohms and checking resistance, it seemed high when touching the negative post and then the frame connection. Also, I don't see any grounds coming from the engine block itself to the frame or firewall. Does this sound right and is it possible the engine does not have any grounds?

 

[Scott91370]

Sounds like there is not a ground to the engine. Usually it goes from the battery to the alternator bracket.

You must be registered for see images attach

 

[Ricko1966]

So, I haven't had time to perform anymore load tests, but I was able to play around with the negative battery cable. It runs directly from the battery post to the passenger side frame rail. Setting the multimeter to ohms and checking resistance, it seemed high when touching the negative post and then the frame connection. Also, I don't see any grounds coming from the engine block itself to the frame or firewall. Does this sound right and is it possible the engine does not have any grounds?

Battery primary ground is supposed to go to block first, then frame and body. The alternator and starter are 2 biggest electrical loads they get priority.

 

[Coop8202]

Thanks Ricko and Scott. I messaged the PO who built the truck and the way I'm understanding it is there are no grounds. Also, he mentioned wanting to replace the battery cables but didn't get around to it. So, I will for sure need to add grounds and reroute some wires but I may replace the cables while I'm at it. Can I order some of the braided ground straps to add a couple of grounds (engine block to firewall, engine block to frame) and use 2 AWG wire for the new battery cables? Also, run the primary battery ground to the alternator bracket instead of the passenger side frame rail? Guessing this would be a good place to start and should in theory fix my issue?

 

[awar]

Factory location for the large part of the cable is to the alternator bracket pictured above. The small #10 pigtail goes to the fender near the battery. There also needs to be a jumper from the frame to the body so the tail lights and fuel gauge works correctly. GM grounds stuff to the frame and to the body. Everything needs a path back to the battery ground.

 

[Ricko1966]

Buy a new negative cable that has an extra lead, run the big cable to the block or alternator bracket,run the small lead to the radiator support. Get 6 gauge eyelet connector run it from block to frame. (Personally I would hook the jumper and main lead to the same bolt. You can and probably should run a small ground wire from cylinder head to firewall .

 

[edgephoto]

Buy your cable here. Much better than parts store crap. You can get the correct size eyelets, colors and correct length. Hardly any more money than parts store universal crap.

I bought mine there and could not be happier. Nice and flexible too.