A four pin box uses a single resistor. A five pin box uses a double resistor. You can use a four pin box in a system wired with a double resistor, but not a five pin box with a single resistor. Fun, huh?
Sounds to me like you've got major wiring issues.
A '90 D150 (V8) would have had a TBI system using a PCM. The PCM also handled the charging system, and if you've eliminated all that, you've got a whole snake's nest of wires to sort through to find the pertinent ones to make your systems functional- both the ignition and the charging system. It also had rudimentary transmission controls to control the O/D and torque convertor lockup, if so equipped.
Ideally, you need to get a factory service manual; or at a minimum, get copies of the wiring diagrams- and then settle in for some investigative reading. You may also need to figure out how to wire your gauges so they work without the computer sending them signals.
But to give you a basic rundown, you need two wires for your ignition:
A "key on" (run) hot feed.
A lead that is hot only when the key is in the "start" position. This can not be the same wire that
activates the starter relay.
This is a basic layout of how the system gets wired, including the charging system with alternator and new electronic voltage regulator:
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