My schematics for that chassis/yr -Fuse 5 is ATA K38 interlock relay coil side. [ assuming you are giving me the correct year 124.032]

OK
There is a 3 wire terminal block/connector to the left of brake fluid resersoir [ on inner firewall]
Unplug that and then jumper a wire from the battery + to the center connector at that plug [ not the connector/harness you unplugged, but the one mounted to the firewall. [ where V/Wt wire went.]

make sure Key is OFF and trans is in P.
Does starter engage w/test?????????????????????

If yes , trouble is upstream from that X27 connector.[ NSS or K38 relay]
.if NO, downstream.. [ starter/sol, etc]

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A Dalton