That positive battery cable should run from battery + to the top lug on the starter solenoid. Engine is a small block Chevy, but I doubt it is original to your '58. I agree that pulling all the under hood wiring and starting over would be a good thing to do. Under dash is probably as ugly. These things aren't that complicated to do yourself.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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