Where can I obtain a wiring diagram for a maytag dg312 gas dryer so I can diagnose correct part, the ignitor is glowing but gas valve not opening
I cannot find a diagram for that model, but in general to trouble shoot your problem you should first check your thermal fuses/thermostats for continuity.
I do not work on gas appliances, so if they are ok, look at the other posts on gas dryers not coming on or staying on this Forum. Almost all of them say to replace the coils.
Good luck, let us know what you find out
The obvious first place to check is: Gas–ON.
One of the common causes of this problem is bad coils. Replacing them will probably fix the problem. You can check them by removing them, but keep the wires attached. Start the dryer and place a screwdriver into the coils, one at t time. If they work, they will be magnetically attracted to the screwdriver shaft. The next thing to check is the continuity of the radiant (flame) sensor. No continuity–replace it.