Losing Electric While Driving

[jc06vmax]

'89 K5 with a 91-93 305/NV3500/208...been daily driving for around 6 months with no issues...purs right along. A few days ago, the lights occasionally flickered and the seatbelt dash light would come on and off...didn't think much about it. Yesterday, the radio cut in and out, had flashing lights, then intermittent complete power failure..both electrical and mechanical. The engine would kill out for half a second or so, then roll on like nothing ever happened. Also gave the occasional backfire after coming back to life. This is only while driving...idles perfectly.

Here's what I've checked so far.
-pos and neg battery connections
-alternator
-all fuses
-computer connections

To me it sounded like an alternator going bad or a bad ground somewhere..but everything checked out good. Strange that it started all of a sudden. Could it be a bad ignition switch and maybe bumps in the road giving it a fit?

 

[76k5blazerr]

Check your fuseable links, I had a similar problem on my 76. You should have 3 or so fuseable links on the truck, one down by the starter and one up on the firewall at the junction block. Check to see if they are blown or loose connections.

 

[dhcomp]

Sounds like a voltage regulator in the alternator, or hte alternator itself.

What have you checked on the alternator?

 

[Stomis]

Fusible link or the connection on the back of the starter could be loose. I actually had a bad lug on a starter one time do this exact same thing to me.

 

[4X4HIGH]

Sounds like a voltage regulator in the alternator, or hte alternator itself.

What have you checked on the alternator?

For the win.

Check battery voltage when this happens and see what it is, i'll bet it is close to 10.2 volts or so.

 

[Kain]

Might also check the firewall main connection to see if its lose

 

[jc06vmax]

Went to check the fusable links (had the same issue on a 71 k5 I had) and found that the big nut on the starter had worked its way loose. Cranked that dude down and its good to go.

Moral of the story: start simple.

Thanks for all the replies...good info here!