Old 1977 GMC Van Wont Start-electrical

Ok, guys. since there are a lot of smart people on here I thought I would throw this issue out to you all and see what ideas come up. Here goes. I have a 1977 van that I use on occasion as a farm truck. Its run mostly on the weekends. Lately it has had an odd issue and I haven't had the time to even look into it yet. So now I am plotting on where to start. Van has a new battery, but lately sometimes when you get into start it up you get nothing when turning on the ignition switch. No lights either. At first I thought it was the batter so I put in on a quickstart 50 amp electrical charger, went back in the cab to try to crank it over and nothing. So I went out and pulled the plug on the charger and when I did, the lights came on and the van started up. Very odd I thought? Why would the quickstart not work or even produce lights but then when I disconnected it, the van started right up and the lights came on?? Well I drive the van around over the weekend and no issues. Then I go to start it up and the same old story. No start and no lights. I try my trick with the 50 amp electrical jump start. This time it doesent work. I thought at first it was an ignition switch problem, but that would not explain the lights not working? I thought it was a zapped battery, but it has 12 volts. I haven't had enough time to check anything else out because its dark when I go to work and dark when I come home and the van is out away from the house now broke down. I am wondering if it is a ground problem? Somewhere the 40 year old ground cable either from the battery to the engine block or if it has one of those engine block to the firewall ground straps is gone or rusted? The alternator is the original one too, however I have not had a time when it has not charged while running. Amp meter on the dash shows somewhere around +12-14 volts when running. Any thoughts on this old GMC would be appreciated. It is ugly but it is my main go to vehicle for the dirty work. AND I don't worry about getting it scratched when I go to Walmart!! LOL!! Bought it for $700 bucks in 1991.

Bad main battery connection. Could be either cable on either end.

When you disconnected the battery booster, you jostled the bad connection enough that it made contact.

Replace both battery cables. It's well past time.

Check the small wire that comes off the positive post battery cable. If it is making good contact check the ground cable to the engine block and the body grounds. If everything looks ok then check the wiring at the starter. John

When it fails to start, and the lights do not work, it is test time. A simple test light will do fine. Ground the test light to the Negative battery terminal. Use the pointy probe to touch the post of the positive terminal, then the terminal itself. Both should light the light. Move on to the far end of the big positive bat cable at the starter solenoid. if it lights go to the smaller wire on that terminal and poke through the insulation to see if power is there (if not there is the issue) if there is power, trace that wire to a relay box and test the components there for power. It is a fault in the power side, not the ground side in my opinion. Wires that look good can be corroded internally Flexing the wiring will caust a temporary "fix" that makes it nasty to find. Jim

Jim, agree with everything you said to test.

The only thing I would add would be to do the testing with the headlight switch on, when they fail to come on. That way the electrical system will have a load on it, and no false readings with the test light.

Bad connection some place e it ground or ignition side of battery. Had that sort of problem on my 1980 Chev pickup once and it was a bad spot on the positive battery cable and it was grounding out just enough to keep it form starting but not enough to cause sparks etc.

That ground cable might ground to the thermostat housing or to an intake manifold bolt which I think were problematic and the side terminal battery bolts to the cables was a rinky dink set up also.

Years ago I bought a used Checker car
Was high mileage , and it would do the
Same things you describe , it was the
Electrical Ignition switch , it was near
Bottom of steering column , completely
Wore out

Hello Fred from MO,

Classic symptoms a bad connection. Loooks closely at the battery cables, and the engine ground. Thats my guess!

Guido.

Steve and Janicholson got it ! Mark

Is it a side terminal battery> They are notorious for this.File the cable ends down a little so the bolts can get a better grip.

I am thinking those have 2 fusible links between the pos. battery cable terminal on the starter and the plug on the firewall. That is what I would check next.

I think these were in the beginning era of fuseable links. May be located down by the positive
battery cable connection at the starter solenoid. Or if I remember right pickups in those years had
a single or possibly double stud on a black plastic connection block on the firewall off to either
side of the distributor(not connecting to it just as a location landmark) used a 3/8" socket and red
wires. That may also be where the fuseable link is. Look for something similar on your van near
the brake booster or heater/AC unit. Since all power seems to be lost intermittently it sounds like a
fuseable link is barely making connection. My $0.02. Good luck.

This is NOT your problem but I recall there was no ground jumper between the motor and frame in my 78 GMC and I added one. At the age of the truck wires can deteriorate as well as brake lines close up .