If You Take The Cover Off The Heater There Is A Small Black Switch That Says Fan Off On. What Should This Be On. If It Is Off The Heater Will Not Blow Or Light Or Anything. If It Is On It Makes A Constant Low Buzzing Sound But The Heater Will Come On And Heat Should It Make This Sound.. THE FAN WILL ONLY COME ON IF THIS SWITCH IS IN THE ON POSITION. The Fan Continues To Go On And Off After The Burner Goes Off. Could I Need A New Thermostat:

If You Take The Cover Off The Heater There Is A Small Black Switch That Says Fan Off On. What Should This Be On. If It Is Off The Heater Will Not Blow Or Light Or Anything. If It Is On It Makes A Constant Low Buzzing Sound But The Heater Will Come On And Heat Should It Make This Sound..THE FAN WILL ONLY COME ON IF THIS SWITCH IS IN THE ON POSITION. The Fan Continues To Go On And Off After The Burner Goes Off. Could I Need A New Thermostat:
This is a Interthern mobile home furnace? Leave the fan on off. It sounds like the draft inducer fan is froze up. If the burner doesn't light the fan won't blow heat.

This is a Interthern mobile home furnace? Leave the fan on off. It sounds like the draft inducer fan is froze up. If the burner doesn't light the fan won't blow heat.
If the switch is in the on position the burner lights and the fan comes on and heats the house. Something just makes a very low buzzing sound it stops the buzzing if the switch is turned to off. After the house is warm the fan shuts off but then continues to go on and off for about 15 minutes.sometimes the fan doesn't come on right away and the burner will go out but it lights again and the fan comes on and heats the house.

I'm still a bit confused. Is this a mobile home furnace? Are you sure this is the fan on/off or the power on/off. The buzzing could just be the transformer. Are the filters clean? Could latent heat built up in the furnace be causing the fan to cycle back on for a minute to remove the rest of the heat. Has the thermostat been changed or tampered with? The heat anticipator could be set wrong, causing it to short cycle.

Sorry not much better help

PS is there a fan on/auto on the thermostat? Set it to auto.

I highly doubt it is the thermostat. Although the thermostat has the fan on switch, in a heating cycle, the fan is controlled by a timer or limit switch and maybe a relay. The relays frequently go bad. Unfortunately, you may have to replace an expensive control board if so.

It is difficult to diagnose noises over the internet. Perhaps you will have to call a tech.

I'm still a bit confused. Is this a mobile home furnace? Are you sure this is the fan on/off or the power on/off. The buzzing could just be the transformer. Are the filters clean? Could latent heat built up in the furnace be causing the fan to cycle back on for a minute to remove the rest of the heat. Has the thermostat been changed or tampered with? The heat anticipator could be set wrong, causing it to short cycle.

Sorry not much better help

PS is there a fan on/auto on the thermostat? Set it to auto.
Product id: f-1008-7
Intertherm rocker switch spdt (631947) this is the part number of a switch that looks like what i am talking about but the one i have has fan on one side off in the very middle and on on the other side

Most thermostats have an Auto/On switch for the fan. In auto, the fan comes on as controlled by the heat or A/C cycle. It is on all the time in the On position. They could have put a switch with the same function in the heater. I am not sure why they would have used a double throw switch with center off. Do you know where the switch was if the system worked in the past? My guess is that the fan position is the same as the usual auto. If the heater doesn't work with it in that position, something is wrong with the controls, likely the fan relay is bad.