Bizarre electrical problem - acts like no battery but can be bump started

[Evan_C]

Okay, first off, thanks to everyone here for any help or suggestions. 
 

I know the subject line seems simple, but it’s a little more to it than that. here goes:

 

-New to me truck. Driven for about 10 hours with no problems at all. 1977 620, stock except for a Weber. 
 

- JDA and the truck stalled due to a crazy lean running carb (had to pass emissions recently and hadn’t got to readjusting.)

 

- upon restart, nothing. Zero. As if there was no battery at all. In both Acc, On and Start. 
 

- I happened to be aimed down hill toward my house so I coasted for about a block. Got bored and tried to bump start it. Fired right up! Ran great. No noticeable issues with ignition. I assumed it was a low battery. 
 

-drove and let it run for about 20 minutes, stopped off at the oriley for light bulbs. Back to nothing. No lights fuel pump, nothing.  
 

-stupidly just bought a new battery, and similar situation, except occasionally the accessories work.  But the starter doesn’t.  
 

Still here? Thanks. So here’s what I’ve looked at:

 

-battery and alternator tested fine. 

-ran batt to starter solenoid and starter spins but sounds like it’s not engaging with the flywheel. Weird? Are those two different circuits/systems? Could one be damaged? Starter appears new.

- truck will consistently bump start

- I’ve only used the turn signals while it runs. I was in a hurry and didn’t get a chance to run through all the other electrical while it’s running.  
 

okay. Hopefully I look like an idiot and this is obvious to y’all. 

 

 

[jagman]

I have driven my 720 for a year and it has started doing a similar thing.  Now when I try to start it in the morning it sounds like the battery has lost it's charge and will barely turn the engine over.  I bump start it and it functions perfectly all day.  Peculiar and with no change to any wiring.  I am with you and hope someone here can offer suggestions.

[datzenmike]

12 hours ago, Evan_C said:

Okay, first off, thanks to everyone here for any help or suggestions. 
 

I know the subject line seems simple, but it’s a little more to it than that. here goes:

 

-New to me truck. Driven for about 10 hours with no problems at all. 1977 620, stock except for a Weber. 
 

- JDA and the truck stalled due to a crazy lean running carb (had to pass emissions recently and hadn’t got to readjusting.)

 

- upon restart, nothing. Zero. As if there was no battery at all. In both Acc, On and Start. 
 

- I happened to be aimed down hill toward my house so I coasted for about a block. Got bored and tried to bump start it. Fired right up! Ran great. No noticeable issues with ignition. I assumed it was a low battery. 
 

-drove and let it run for about 20 minutes, stopped off at the oriley for light bulbs. Back to nothing. No lights fuel pump, nothing.  
 

-stupidly just bought a new battery, and similar situation, except occasionally the accessories work.  But the starter doesn’t.  
 

Still here? Thanks. So here’s what I’ve looked at:

 

-battery and alternator tested fine. 

-ran batt to starter solenoid and starter spins but sounds like it’s not engaging with the flywheel. Weird? Are those two different circuits/systems? Could one be damaged? Starter appears new.

- truck will consistently bump start

- I’ve only used the turn signals while it runs. I was in a hurry and didn’t get a chance to run through all the other electrical while it’s running.  
 

okay. Hopefully I look like an idiot and this is obvious to y’all. 

 

 

 

Don't assume anything...

Clean and tighten the battery terminals, replace if they don't clamp properly.

Clean and secure the negative cable where it bolts to the head and the positive cable where it bolts to the starter lug. While at the starter make sure the single small Yellow/Black (stripe) wire is firmly connected to the solenoid.

 

You should be able to reach up from under the steering column and unplug the ignition switch. I'm pretty sure I used to do this to disable my 620. Plug it in several times to clean the contacts. It may even be loose.

 

That should get it going or perhaps point to something else.

 

 

 

 

[SWFL]

Clean grounds are your friends. Brushes wear out in both alternators & starters. They are usually not too hard to replace.

 

Here's an odd one. The early VW Rabbits had a terrible weak fuse panel. An older worn radiator cooling fan could cause a partial meltdown on it. Same with leaving the rear window defogger on too long. There was other BS with them that I've forgotten about. One morning I jumped in my Rabbit and it didn't start normally, which it would fire instantly due to being fuel injected. It cranked and cranked, but sputtered a bit when I let off the key. Ok, no problem  it's probably a bad coil or ignition control module. I get my test light out to check the wiring to the coil. When I cranked it, the light went out, until I stopped cranking the starter? I jumped the hot side of the coil to the + of the battery. It fired up like normal. Turns out the rear window defogger circuit melted down, and somehow corrupted the ignition circuit, so when the starter was cranking, the coil got no power, but when the starter wasn't cranking, the coil had power. I replaced the fuse panel and saved the old one to cut apart. I never did and tossed it when I got out of VWs.

[Evan_C]

On 3/14/2023 at 7:30 AM, datzenmike said:

Don't assume anything...

Clean and tighten the battery terminals, replace if they don't clamp properly.

Clean and secure the negative cable where it bolts to the head and the positive cable where it bolts to the starter lug. While at the starter make sure the single small Yellow/Black (stripe) wire is firmly connected to the solenoid.

 

You should be able to reach up from under the steering column and unplug the ignition switch. I'm pretty sure I used to do this to disable my 620. Plug it in several times to clean the contacts. It may even be loose.

 

That should get it going or perhaps point to something else.

 

Thank you @datzenmike Lesson learned about the assumptions. 

I'll go through and check all the connections related to the battery, starter and ignition switch. That is definitely the zone of darkness. The truck is back to running consistently, but i've found that when it does cut-out like that, if I grab/wiggle the POS lead junction where it connects to the starter and in several other directions, that the truck immediately starts up. 

My current thinking is that maybe the fuesable link is only partially burned out, and that wiggling it around is reconnecting the internals. OR that i'm actaully pulling on some other weak connection, ie. gounds, starter, etc...

As well, i've started to go through and remove or cap all loose wires. Looks like someone was running power to the cab directly off the battery (at least it was fused) but the end was just dangling under the dash. Lots of that sort of junk going on.

 

I'll update when i feel confident i've rectified the issue. 

[bigboy620]

Fusible link? I had one burn out on my and it gave me. No start issues.

[Evan_C]

On 3/26/2023 at 9:22 PM, bigboy620 said:

Fusible link? I had one burn out on my and it gave me. No start issues.

I'm pretty sure that was it! I replaced the fuseible link with a fuse and everything seems to be working now!

[datzenmike]

Carry lots of extras so you don't get stranded somewhere. The fusible link will carry a dead short for several seconds. A metal fuse will pop much sooner.