Resolved HVAC Control Lights not working

So I just got done installing my new 5.0 Resto DD “Factory Inspired cluster in my 89 GT and while I had everything apart I also replaced my hvac controls entirely because my old set was missing a mounting tab and the face of the temp control was gouged.

When turning on the headlights, the gauge cluster lights up as it should but the hvac controls don’t. The old ones lit up and worked fine and I even transferred my old LED bulbs to the new one.

Does anyone have a diagram for the lighting on the HVAC controls or maybe which wire to check power for? I should also mention the dimmer switch is new and works fine.

Mustang5L5 said:

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Excellent! Just what I was looking for, thanks. So it seems like my problem is at the light blue/red wire at the HVAC controls themselves. With the lights on and the dimmer on high, I’m getting 11 volts (used a janky ground for testing so the voltage is probably artificially low) at the lb/red wire on both the back of the dimmer switch and the back of the headlight switch.

However when testing the lb/red wire at the back of the hvac controls themselves, I’m only getting .3 volts. Maybe I botched something when installing the cluster but I’m not sure. I tested for continuity between the LB/R wires at the back of the controls and between the switch and dimmer and it’s got continuity.

I’m kind of at a loss now but I’ll double check my wiring to see if I botched something at the cluster connector when installing the DD cluster.

Update: figured out the problem. Due to the extremely vague instructions given in the LMR specific cluster packet, it doesn’t say that the LB/R wires at the cluster connector still need to be connected to each other somehow but they definitely do.

Thanks to the diagram I was able to see how everything is sort chained together with the LB/R wires and the chain was broken right after the instrument cluster connector.