All above are correct
In addition, if everything blinks, replace the headlight switch.
I agree about the grounding problem. In Auto-Shop, I teach my students about the "Grounding Triangle". A three way ground between battery, chassis, and engine. If you are missing any one of the three, and/or your existing connections are dirty/painted/terrible, you will have the blinking lights. So many restorations make everthing look great, at the sacrifice of functionality. Add the extra wire from your battery to the uni-body. Do you still fabe the braided strap from the rear intake to the firewall? Neg batt cable to engine block - NO PAINT on the connection and wire-brushed clean? That connection being bad will also give you starting problems.
And on the Plus side, how good is your battery? Alternator output and regulator performance. If you are just barely making voltage, and sudden drain will also result in the dimming result you see.
Break out the meter and start checking everything.