Hate to disagree with the experts here, but I don't think there is any diode in the charging system.
There is supposed to be a "resistance wire - 15 ohms". It connects between the tan wire on the alt and the yellow wire that connects to the ignition switch and the dash gauge.
I'm looking a the schematic, for a 4.2L, and I don't see any diode in the wiring. All the diodes are internal to the alt.
Dodge did not build my Jeep.
1988 Wrangler,4.2L I-6, Howell EFI JP-1, 5 Speed Peugeot, Zone 2.5" lift + 1/2" booms, BFG 31 x 10.5, Bestop.