Light is on all the time but won't operate

I had a similar problem once with an older Kenmore microwave, which at the time, were actually made by LG. After removing the cabinet, there was a small automotive type fuse in a clip-in fuse holder which proved to be "open" after checking it for continuity with a test meter. I replaced the fuse with the EXACT type and rating, and continued to use the oven for several more years until I gave it away. Please note, that microwave ovens are not something that you want to mess around with. Make absolutely certain that you have unplugged it before doing anything. In my case, I suspect the after several years of trouble-free use, the fuse had failed, -likely due to age. In your case, it may be a similar issue, so you might want to see if your microwave oven has a similar replaceable fuse. Beyond that, I would strongly suggest taking it to an approved service facility. Also, NEVER operate the microwave until you have replaced all covers, cabinet, etc. to it's original state.

there is a switch that operates it must be bad most time door switch

This can be due to wrong choice or fault in the power supply ,main board or the magnetron.
You should try with a preset selection and if the microwave works then the fault relates to correcting the power to time settings.
Check out with microwave cooking tips.

The magnetron may be defective. You can replace the magnetron, there is no other possibility.

The problem is in the magnetron or the inverter board if 7 years old or less.

The problem is a magnetron, "heart of the system" or the inverter board, "if 7 years old or less" and possibly the keypad control board, all of these items are not cheap and lethal voltages are present.

Usually, power for the turntable motor and the magnetron tube (the microwave source) are controlled by a couple of things. One is a relay on the control circuit board, and the other is a switch that's operated by one of the door latches. It's possible the control board has gone bad or bad connections have developed. It's also possible the door switch has failed or is out of adjustment and the oven thinks the door isn't closed.

Diagnosing this kind of trouble may require working on the oven while it's operating. MICROWAVE OVENS USE HAZARDOUS VOLTAGES WHICH CAN KILL YOU. You might want to leave the repair to a professional because of safety concerns. Unless the circuit board requires replacement, it's probably worth having this repaired. Unlike some repairs, this one won't cost as much as a new oven.

You know I just had a similar problem on my old unit. There was a spark and my bowl had no metal rims. I figger your ground connection has corroded at the rivets. So if you can drill a 1/8 inch hole in there and install a #8 sheet mtal screw or two to bond it togeter again.

Have GE JVM1440BH light and fan that are operated by the touch pad do not work. Both stop working at the same time. Ideas????