[ray_mcavoy]

To make the stock gauge cluster fully functional in a truck that was originally equipped with a warning light cluster, you would ideally swap 4 of the wiring harnesses. Those being:

(1) The engine harness (that you purchased)
(2) The alternator / headlight harness
(3) The cab / under-dash harness
(4) The instrument cluster harness (you might already have this if it came with the cluster)

So that leaves you with the "alternator / headlight" and "cab / under-dash" harnesses that won't be compatible with the gauge cluster. American Autowire does make reproductions of these harnesses in their "Factory Fit" line of wiring that will work with the gauge cluster. They would be a direct plug-in swap and work with the gauge-style engine harness you have already purchased.

Note that the existing "alternator / headlight" and "cab / under-dash" harnesses can be modified to work with the gauge cluster. So that might be something you would want to consider (even temporarily) to get everything working.

American Autowire also makes a "Classic Update" line of wiring that is a complete kit. If you eventually plan on re-wiring the truck with one of these kits, you wouldn't need the separate engine harness. However, I don't think the Classic Update harnesses support the battery gauge (ammeter) in the gauge cluster ... you have to either leave it unused or swap it out for a voltmeter.