dead electrical circuit

I have a 69 van i'm trying to get started. i can jump the posts at the starter to crank the engine, but there is no power to the ignition switch. I have some power to the fuse block, all the time, but no accessory circuit voltage when the ignition is turned on. I looked over the wiring print, and I don't know where the junction is that is shown on the print that the red wire feed everything. It shows about 4 wires coming together at some junction, but I don't know where the location of that junction is in this van. Can anyone that has trace out the electrical system let me know where this junction is, please?

You never know what people have done over the years,,,,,,but see what you got,,,,,,the system starts with a fusible link on the positive battery cable on the starter solenoid,,,,,(then turns into a 12 gauge red wire), then it goes to a junction block,,,,then it splits off to go to the alternator output and voltage regulator,,,,it continues to a 6 wire connector, then it splits to the ignition switch, to the headlight switch, the fuse box and then horn relay,,,,,,,,,,you should have 12 volts at all times on these wires,,,,,,see what you get,,,,,,you say you dont have power at the ignition switch connector?

That's correct donivan65. I am looking for the exact location of the connection point so i can get power to the Ignition switch. The alternator B+ output wire has power, and the fuse box 12 volt constant power circuit is ok also. with the key switch on, there is no power to wipers, heater fan, radio, etc. also the headlights don't come on either. if I find that junction point, i believe I will have found the open circuit that feeds those components. The junction block is powered up also, so I believe the fusible link is ok.

Have you checked the harness plug coming out of doghouse ??(on driver side under seat) Or also check the wires running along floor (in plastic by hump) Look for a 12 gauge red wire. "Think" Thats the one that feeds HL & ing. switch. Bad thing GM made splices (soldered & taped) where it was close to branch off to other feeds .(save wire???) Hope this Helps some???

Maybe backfeed some 12v back into the feed wire in the ignition switch connector and see what comes on or dont,,,,,or jump across the feed wire and horn wire at the horn relay and then wiggle, twist, push and shove the wiring loom so the horn would blow if you maybe hit a broken spot..,,,,,,

Well further investigation today got me a little further. (thank you everyone for your suggestions, it gave me ideas to dig into) I discovered that the neutral safety switch wan not letting voltage go through to the starter solenoid because the Previous Owner had removed the linkage to it. (don't know where its at) I temporally bypassed it and the engine now cranks with the key. The next discovery is that the horn relay activates when it should. Too bad the horn doesn't blow. I still have no headlights, instruments lights, wipers Etc. next step is to check for power at the dimmer switch. Keep the suggestions coming, with all your help I'm determined to bring this van back to life.

Good to hear you making progress on your van
Here is pic of backup/ safety switch. on a 68 with 307 & PG.  Not sure if 350 trans is same???
Coat hanger isn't stock   Only using it for backup switch

In had problems with dimmer switch. Sometimes if you push it a bunch of times it will come on.
What kind of shape is your fuse box in? Had problem with them corrading where fuse pushes in.

The fuse box is in fair shape. It shows some rust, but a circuit tester shows all the fuses have contact through them. The only dead one is the fuse for the lights. My biggest issue now, is finding the linkage for the neutral safety switch. I spent the day at the wrecking yard gathering little incidentals for this project, but could not find the linkage anywhere. I hope someone on here has a spare that they can sell me. By the way, the photo is a Great help.

I've been working most days on the van, and today made a lot of progress. I dot most of the electrical sorted out, and I now have spark to the spark plugs while cranking the engine with the key, instead of jumping the starter. If things go as planned, tomorrow I rebuild the carburetor and install it. THEN it's the first attempt to fire it up, after sitting for over 28 years. I can hardly wait.

Well Today was a GREAT day. Got everything done to attempt starting the engine. I'm glad to report it runs Fantastic. I must admit i'm a bit surprised that it started so easy and ran this good after sitting for almost 3 decades. I hope putting Marvel Mystery oil in the cylinders a week ago helped. Now it's on to cleaning the fuel tank and radiator while finishing up the brakes, then a test drive. It feels Sooo good bringing a van back to life. I may even put new hoses on the Air Conditioner and get it operational, since that's my specialty.