Problem could be anywhere. Timer problem, broken wire, faulty element or faulty thermostat. Unless you have test meter, tools & fault finding ability, which you haven;t stated on here, then call out an expert service company. That is if you want to spend money on such an old appliance.
Lincoln Appliance NZ
March 2018
Automatic Answer
While you wait for answers, we may have found some information which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix tumble dryers.