[ray_mcavoy]

There are 5 wiring harnesses that need to be changed or modified when swapping from warning lights to a gauge cluster.

(1) The small harness that's on the back of the cluster is significantly different between warning lights & gauges. However, these harnesses are often left attached to the back of the gauge clusters so you may already have this one.

(2) The tachometer has it's own separate harness. Again, you'll need to get one of these unless one was already included with your gauge/tach cluster.

Note: The 60-62 factory tachometers used an external sender. While the 63-66 tachs have all of the electronics located inside the tach assembly. Externally, they both look very similar but the wiring harnesses & connections are significantly different.

(3) The cab harness (which includes the fuse box) has a few minor changes. Most important is the re-routing of a couple wires to work with the "BATT" gauge (ammeter) instead of a "GEN" light.

The 63 cab harness used with warning lights has a brown wire for the "GEN" light that shares a common terminal on the LH bulkhead connector with the 10Ω resistance wire (brown with white stripe) that comes from the ignition switch. And there is an unused cavity in the LH bulkhead connector.

While the 63 cab harness used with gauges has a red (instead of brown) wire for one leg of the ammeter circuit. It follows the same route as the brown "GEN" light wire and can be re-purposed as such. However, you need to cut the resistance wire (brown w/white stripe) from the shared terminal (leaving the brown wire alone), crimp a new terminal onto the resistance wire, and insert it into the formerly unused cavity in the bulkhead connector.

The cab harness used with warning lights also has a leg of the "HOT" light circuit going to a grounding contact on the ignition switch to perform a "bulb check" when cranking the engine. If that connection is left in place when the "HOT" light wire is re-purposed for the temp gauge sender, it will cause the temp gauge to jump to the hot side when cranking the engine. That won't do any harm, but disconnecting that wire from the ignition switch "GRD" terminal will prevent it from happening.

(4) The engine harness used with gauges has a black wire (with an inline 3A fuse) that connects to the starter solenoid BAT stud. This forms one leg of the ammeter (BATT gauge) wiring. And it has a different connector on the dark green wire for the temp sender.

(5) The front light / alternator harness used with gauges has the brown wire from the #4 regulator terminal hooked to a different cavity in the LH bulkhead connector. This joins it to the 10Ω resistance wire in the cab harness. And it contains an additional red wire that connects to the junction block on the horn relay for the other leg of the ammeter. Although not factory, I highly recommend adding a 3A inline fuse to this wire as well.

In addition to the wiring changes, you'll also have to swap out the temp sending unit for one that works with the gauge instead of warning lights. And add steel or copper tubing for the mechanical oil pressure gauge.