I've written some XML code that fixes the AP yoke disconnect button and the AP disconnect light.

About the switches:
Any one of the 3 switches can get 'stuck' (not my fault) if you click on it and then move your mouse at the same time. A quick, steady handed mouse click seem to to the trick.

On the AP Disconnect Light:
It was necessary to place a 6 second timer for the light display. You can press the AP reset button at any time during these 6 seconds to extinguish the light if you choose.
Somewhere in the CS737 code is a value to keep the light off and without the timer, it would be the equivalent of toggling the light off and on until the warning is cleared.

I'd rather not provide another XML gauge right now, so he easiest way to install this fix would be to paste it into an existing gauge.

If you've installed the CS737_APU_Gen_GrdPwr_Mod you can copy all of the code below and replace / paste (yellow highlighted section is new).
Make a backup copy first!!!

<Gauge Name="CS737_APU_Gen_GrdPwr_Mod" Version="1.0">
<!-- FSX APU-Generator and Ground Power Control 11-JAN-2013 paultally@att.net -->
<Comment>
APU_STARTER                 Start up the auxiliary power unit (APU)
APU_OFF_SWITCH              Turn the APU off
APU_GENERATOR_SWITCH_SET    Set the auxiliary generator switch (0,1)
</Comment>
<Element><Select><Value>
<!-- Check for Gnd Pwr and Gnd Pwr Switch -->
	(L:E_GRD_POWER_ON,bool) 1 == (L:O09_003_SW2,enum) 1 and if{ 1 (>L:GrdPwrOn,bool)
	(L:ApuGenOn,bool) 1 == if{ 0 (>K:APU_Generator_Switch_Set)
							   0 (>L:ApuGenOn,bool) }
							1 (>L:BatteryCharger, bool) }
							els{ 0 (>L:GrdPwrOn,bool) 0 (>L:BatteryCharger, bool) }

<!-- Check if Battery Pwr is Good and if Battery Bus Circuit is Active -->
	(A:Electrical Battery Voltage,volts) 18 &gt; (L:E_BATT_BUS,bool) 1 == and if{
	(L:O17_001_SW3,enum) 2 == if{ (L:Apu_strt,bool) 0 == if{
									1 (>K:APU_Starter)
									1 (>L:Apu_strt,bool) } }
	(L:O17_001_SW3,enum) 0 == if{ (L:Apu_strt,bool) 1 == if{
									0 (>K:APU_Off_Switch)
									0 (>K:APU_Generator_Switch_Set)
									0 (>L:Apu_strt,bool) } }

	<!-- Check if APU is Ready, Check if Appropriate Bus Switches Closed -->
	(L:E_APU_on,bool) 1 == if{
		(L:E_AC_TRANS_BUS_1,bool) (L:E_AC_TRANS_BUS_2,bool) and
		(L:E_DC_STDBY_BUS,bool) (L:E_AC_STDBY_BUS,bool) and
		(L:E_AC_GEN_BUS_1,bool) (L:E_AC_GEN_BUS_2,bool) or
		(L:E_AC_MAIN_BUS_1,bool) (L:E_AC_MAIN_BUS_2,bool) or if{
		(L:ApuGenOn,bool) 0 == (L:GrdPwrOn,bool) 0 == and if{ 1 (>K:APU_Generator_Switch_Set) 1 (>L:ApuGenOn,bool) } }
		els{ (L:ApuGenOn,bool) 1 == if{ 0 (>K:APU_Generator_Switch_Set) 0 (>L:ApuGenOn,bool) } } }
		els{ (L:ApuGenOn,bool) 1 == if{ 0 (>K:APU_Generator_Switch_Set) 0 (>L:ApuGenOn,bool) } } }
		els{ (L:ApuGenOn,bool) 1 == if{ 0 (>K:APU_Generator_Switch_Set) 0 (>L:ApuGenOn,bool) } }

	<!-- AP Yoke Disconnect -->
	(L:W01_001_BUT,bool) (L:W02_001_BUT,bool) or if{
		(L:AP_Yoke_Disc,bool) 0 == (A:Autopilot Master,bool) 1 == and if{ 0 (>K:AP_MASTER) 1 (>L:AP_Yoke_Disc,bool) } }
		els{ 0 (>L:AP_Yoke_Disc,bool) }

	<!-- AP Reset Button / Light -->
	(A:Autopilot Master,bool) 1 == if{ 1 (>L:AP_cond,bool) (P:ABSOLUTE TIME,seconds) 6 + (>L:AP_Reset_timer,seconds) }
	(L:AP_cond,bool) 1 == (A:Autopilot Master,bool) 0 == and if{ 1 (>L:L10_001_LT,bool) }
		(P:ABSOLUTE TIME,seconds) (L:AP_Reset_timer,seconds) &gt; (L:L10_001_BUT,bool) 1 == or if{ 0 (>L:AP_cond,bool) }

</Value></Select></Element>
</Gauge>