64 F100 strange interior wiring issue

[64steve]

I have a 1964 F100 and have a weird problem , when ever i put a load ( headlights brake lights or turn signal) my interior lights flash along as if i’m having a serious voltage loss , my voltage gauge connected to the fuse box also drops and goes up with the turn signal , i thought it was a ground issue so i had added grounds to make sure and nothing. it’s very weird as everything works as should but it seems like something in the interior and maybe fuse box is cutting out , i tried using a power probe on the fuse box and noticed the voltage fluxing and also does it with key on engine off.

 

[dmsfrr]

Have you double checked all the power wire connections between the positive battery cable and the fuse box?
Where is the other end of the Negative battery cable attached to the truck?
Is there a large-ish ground wire with clean solid connections from the body to the engine?
Where did you add ground wires?
.

 

[64steve]

hello i’ve been away from my computer due to school and work but i appreciate you responding , but since i posted this ive done a bunch of tests , i tried a headlight switch to no avail , i checked my grounds and voltage drop tested them and had .02v which im happy with , i checked the black and yellow wire from the starter solenoid to inside to the ignition switch and seems fine , one thing i did not like is the 75 amp fuse that is suppose to be inline is missing and they had cut and soldered a new piece of wire that has a newer style 40 amp fuse , i’ve kinda given up and ordered a new ignition switch from work and if it doesn’t work it’s going back together and just going to live with it , i’ve kinda exhausted all my resources to no avail

 

[Bleach]

Are you still running a generator? I think ’64 still used one. I would have it checked out and the regulator.