Changed the Speedo cable yesterday, and I must have dislodged a primary power source. I have no power what so ever, my battery is fully charged, I tested it with a volt meter. I have no lights,ign etc. ?? There is a heavy duty Yellow and Purple plug under neath the dash that might have something to do with it ?? I just cannot figure where it connects. Any help would be most appreciated 

Scott, I had the same problem with my 66 once. Turned out to be where the wiring harness plugs into the fuse box on the firewall. Somehow it was loose.

 

I see a yellow wire(from the ign. switch), and a purple wire from the neutral safety switch, that comes directly from(to) the starter. This would not kill the entire electrics, only dis-able the starter. It is the only connector I see with a yellow and purple wire.
It is possible that one of the fuse-links has blown, and killed the system. Check to see if there is any power at the fuse box.

How about I just went out to check on the car and the power is back ?? The radio  settings are all off so there must have been a supply disconnect some where ?
Very    confused

Adam,
by the way, before there was no power anywhere except directly off the battery. I have aux items connected to the fuse panel and they were not working.
Prior to this not a problem ??

Sounds like a loose connection either at the batt., or the starter. Could be power(12v+) or ground. Check the batt. terminals carefully, as well as the connections on the starter. If this happens again, check for power at the alt. This will tell if it is a batt. connection or not.

I still wouldn't rule out a fuse-link. They can work one time, and not the next. Adams' Apple38935.4794212963

Joel,
where is the main fuse link for the 78. I checked the alternator, no power, I have lights and an aux horn wired directly to the fuse panel, nothing. Have a high end stereo system ? Do not know if this would have an effect ? The battery always showed power, that is why I am confused.
The power kinda just came back on, so if there is something to replace, please tell me where it is, especially if it can be intermittant.
thanks

Scott;

I had the same problem with another GM vehicle.  If you have a side-post battery with female connectors in the battery, the lead female piece in the battery can break loose and cause intermittent power outages.  It is hard to find until it breaks completely loose, then it is easy to find.  I kept losing my radio sets and the interior lights would dim out and you would sometimes hear a zap type sound.

Once I changed out to a post-type battery and ends, I never had the problem again. 

Dennis

Scott, there are two fuse-links coming from the starter to the fusebox, and interior. You will need to get under the car to check them. They are normally about 8"-12" up from the starter, sometimes closer. Check to see that there is power on both sides of the fuse-link.
I have pics somewhere...I'll have to see where I have them "stored", and will post them later, if it will help.

If you could that would be great. I can get new links at any auto parts store ? or do I need to go to GM ?