No power like it is running on 12 volts need to know how to wire for 24 volts

Remove all the low voltage control wires from the thermostat, on the terminal board there is ,
R or Red = 24 volt "hot leg"
W or White = Heat circuit.
Y or Yellow = Cool circuit
G or Green = Fan circuit.
C or Common = 24 volt "neutral leg"

The R and C terminals are the 24 volt power supply, the R being the hot leg of power, C is the side of power that every 24 volt circuit terminates upon to complete the circuit.
Just as a car battery has a Negative post that all 12 volt circuits terminate upon in a car or anything electrical , they all require 2 legs of power, some voltages are only 1 hot leg 230 volts is 2 hot legs but 115 volts and 24 volts which a thermostat controls uses 1 hot leg being the R terminal.
The thermostat has switches internally that connect the hot leg of the 24 volt power to the desired circuit, jump red to white and heat comes on, jump red to green and fan runs, jump red to yellow and the AC unit outside runs. test this out and if it operates then the thermostat is bad assuming it is wired correctly.

get a 12v to 24v converter
as an example see link below
https://www.ebay.com.au/itm/12V-to-24V-DC-to-DC-Step-Up-3A-Power-Converter-Module-/261044512143

It is likely to be a function of the switch to place both batteries in parallel in the 12 volt position and in series in the 24 volt position - this is likely to make the switch and the wiring fairly complicated as the motor could be wired internally in a variety of ways and the switch will also need to send the right voltage down the right wires.

I suggest you first ensure both batteries are fully charged and in good order. Once you are certain of that it is time to inspect the switch and wiring and test the voltages. A wiring diagram would make the task much easier.

It depends on how it and the wheelchair are wired and how the voltage is derived.

Presumably the 24 volt wheelchair requirement is provided by two 12 volt batteries connected in series and these could be recharged in series by a 24 volt charger and a pair of wires or by a 12 volt charger providing a 12 - 0 - 12 using three wires where one 12 is a positive in relation to the 0 and the other is a negative in relation to the zero making a potential difference of 24 volts.

There could conceivably be circuitry within the wheelchair that requires only 12 volts for recharging and causes the two batteries to be charged separately, though while this method could be desirable and offer some benefits it would be considered unnecessarily expensive and complicated for most commercial purposes.

As usual you really need to know what is supposed to happen or is designed to happen before fault-finding can begin. One of the wires could be a safety ground wire but most likely it is used to provide some sort of feedback to the charger from, perhaps, a thermal switch close to the batteries so charging will cease if too much heat is generated.

Yes, possibly, if you have wall thermostat. If controls are all at ceiling/manually, then 120VAC power should be all you need. If wall thermostat, you will require 12 VDC, or 24 volt transformer system for it to operate. Usually towables have 12 volt, and park models etc, use a 24 volt transformer in the system. If you hear clicking when trying to run it, on off etc, check 120VAC source, such as breaker wiring to it .

http://www.itwinkle.com/hp57posub.html

Nothing special about that Power Supply except for the PRICE!

It's just a regular ATX SMPS with a 575 Watt maximum rate wattage, and an 8-pin EPS +12 Volt power cable.

The HP part number is HP 405349-001
I just THOUGHT the above model was expensive,

http://www.sears.com/hp-405349-001-hp-575watt-power-supply-for-workstation/p-SP101A9790S5492818201P

Uses one 24-pin ATX main power cable,

http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24

One 8-pin EPS +12 Volt power cable,

http://www.playtool.com/pages/psuconnectors/connectors.html#eps8

[NOTE*
NOT to be confused with the 8-pin PCI Express power cable,

http://www.playtool.com/pages/psuconnectors/connectors.html#pciexpress8

Yellow wires are 12 Volt wires. Black wires are Ground (Negative) wires.
The 8-pin EPS +12 Volt power cable has FOUR 12 Volt wires.
The 8-pin PCI Express power cable has THREE 12 Volt wires ]

I believe 4 SATA power cables,

http://www.playtool.com/pages/psuconnectors/connectors.html#sata

,and a few 4-pin Peripheral power cables, ('Molex'),

http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral

Power Supply case dimensions are approximately
6 Inches Wide, 5.5 Inches Long, and 3.5 Inches in Height.
(152.40mm Wide, 139.70 Long, and 88.89mm in Height )

36 Amps combined for the two 12 Volt power rails.
(12V1 = 18 Amps, 12V2 = 18 Amps)

This is an example of a replacement SMPS,

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=899124&CatId=1483

I'm running one of these right now in a Dell Optiplex 745
Yes, even though the power cabling noted on the Tigerdirect ad is erroneous, it DOES have an 8-pin EPS +12 Volt power cable.

One 24-pin ATX main power cable
Four 4-pin Peripheral power cables
Six SATA power cables
One Small 4-pin Peripheral power cable. (Used for a Floppy Drive, or a Card Reader)

Two 12 Volt power rails. 12V1 = 23 Amps, 12V2 = 20 Amps
Combined = 43 Amps on the 12 Volt power rail.

Repair?
Due to the possible electrocution hazard, I don't post info on repair.
I will state;
The capacitors need to be PROPERLY discharged, before attempting to work on the unit.
The Radial Aluminum Electrolytic Capacitors are the weakest link.


For additional questions please post in a Comment.

Regards,
joecoolvette

Well here is a way to check your power supply, on your hard drive connector using your volt meter and measuring from ground. this would be using one of two middle connectors it should measure +5 VDC on the red wire and + 12 VDC on the yellow wire. If these voltages are good then we got to see if the power supply is producing the -12VDC voltage. This voltage is ussed by the syustemboard on pin 14 of a 24 pin power supply. I would recommend not having your system board plugged in while measuring these votlages, but the power supply may need a load, I would plug in the cdrom.. Below are a couple of picture to explain this and a link to a website that has this documented.

http://www.playtool.com/pages/psuconnectors/connectors.html

The 24 pin main power connector was added in ATX12V 2.0 to provide extra power needed by PCI Express slots. The older 20 pin main power cable only has one 12 volt line. The new 24 pin connector added one line apiece for ground, 3.3, 5, and 12 volts. The extra pins made the auxiliary power cable unnecessary so most ATX12V 2.x power supplies don't have them. The 24 pin connector is polarized so it can only be plugged in pointing in the correct direction.
Pinout Pins 1 through 12 Pins 13 through 24 Description Wire color Pin number Pin number Wire color Description +3.3 volts orange 1 13 orange +3.3 volts +3.3 volts orange 2 14 blue -12 volts ground black 3 15 black ground +5 volts red 4 16 green PS_ON# ground black 5 17 black ground +5 volts red 6 18 black ground ground black 7 19 black ground PWR_OK gray 8 20 white -5 volts (optional) VSB +5 volts purple 9 21 red +5 volts +12 volts yellow 10 22 red +5 volts +12 volts yellow 11 23 red +5 volts +3.3 volts orange 12 24 black ground
Good Luck I hope this helps.

here is a wire diagram. follow the pictures. you can do fuses but i like inline breakers. you can get them at your local outboard dealer.

Are your electric brakes rated for 12 volt or 24 volt, that is the question. YOu have to supply the voltage at whatever the brakes are rated for.