How do I hook up a ground wire to my new furnace when my house wiring does NOT have a seperate ground wire?

my new Carrier requires,I guess, a seperate ground wire to ground the unit. My house wiring doesn"t have a seperate ground wire coming to the furnace so I"m not sure what to do? It seems to work fine without one but I was advised from a heating practice that there needs to be one. I tried hooking the... show more my new Carrier requires,I guess, a seperate ground wire to ground the unit. My house wiring doesn"t have a seperate ground wire coming to the furnace so I"m not sure what to do? It seems to work fine without one but I was advised from a heating practice that there needs to be one. I tried hooking the white, neutral?, wire and a seperate ground wire, from a green gound screw togather to the white wire coming from the fuse box and furnace ignighter will not come on. When I unhook the seperate ground wire the furnace works again. Any Ideas as to what I should do, short of calling a heating company which I DON"T want to do...? Thank-You!
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