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You have miswired a switch loop. You are actually turning on the switch. Did you "fix" a problem when you found a white connected a bunch of blacks at the fixture? It is supposed to be connected to the blacks.
 

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Discussion Starter · #9 ·
You have miswired a switch loop. You are actually turning on the switch. Did you "fix" a problem when you found a white connected a bunch of blacks at the fixture? It is supposed to be connected to the blacks.
When I turned on the power after I originally hooked up the switch it was set to on and I thought everything was fine, then I turned it off and the breaker went off. So, I switched the black and white wires on the switch and turned the breaker back on and the light worked and when I turned it off, the breaker went again. The old heat fan that was there ha2 2 sets of romex going to it. One set went to a plug and the other went to another plug and those plugs connected together to give the fan power. One of the romex goes to the switch and I think the other one goes to a vanity light that's in there, but I'm not sure. I put the 2 blacks and connected them to the black and red from the lamp and the 2 whites and connected them to the white from the lamp. Are you saying that one of the whites should have gone to the blacks and red?
 

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Tell us ALL the cables and how they are connected at the light.
Tell us all the cables and connections at the switch.

You could also do this test. Disconnect one of the wires from the switch and cap it. Turn on the breaker. I am going to bet the light comes on.
 

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Discussion Starter · #11 ·
I tried to insert a drawing, but it didn't work. There are 2 pieces of romex going to the heat lamp (there was an in ceiling heater there before). One of those pieces goes to the switch and the other one goes either to the exhaust fan or the vanity light. There are 3 switches on the wall--one controls the vanity light, one controls the exhaust fan and there was a sort of thermostat that turned the old heater on. I took out the old heater and was left with 2 blacks, 2 whites and 2 grounds, in the ceiling. I put the 2 blacks together and connected them to the black and red from the lamp and put the two whites together and connected them to the white from the lamp.
 

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Disconnect all four wires up at the heat lamp.

Turn on the breaker. Measure the voltage between every combination of two wires (excluding ground wires) up there. Flip the switch and repeat these measurements.

You should find that exactly one combination shows 120 volts and it is the two wires from the same Romex cable (that goes to the power source).

Now measure voltage between ground and each black or white wire in turn. Only the black that gave a 120 volt reading should give a 120 volt reading this time.

Turn off the breaker.

If everything checks out as I described then connect the other black wire (without a 120 volt reading) to the heat lamp black. Connect the white from the hot Romex cable to the heat lamp white. Connect the remaining two wires (one from each cable, one black, one white) together. (The cable with no hot readings went to the switch)
 
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Discussion Starter · #18 ·
There is a double box with the vanity and fan switch in it, but they work independently. Then above, there is a single bod that had the thermostat control for the old heater and that only has black and white romex. The only red wire that I see is from the heat lamp.
 

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I can reach my hand up in the ceiling and tell which piece of romex is going to the switch and which is going elsewhere. Will that tell me which wires go where?
If you can tell then why are you asking. However I am led to believe that the first sentence is false and that you must do voltage measurements.

One more test. After doing the voltage measurements, turn off the breaker. NOw set the meter to ohms or continuity and test the two wires of the cable that showed no voltage. It should show no continuity when the switch is off and show continuity (near zero ohms) when the switch is on. Twist the thermostat knob to see if anything changes. Never do ohms or continuity or resistance checks on a live circuit.

When you said that the heat lamp has a red wire, does it also have a white wire and a black wire? What does its instructions say about the three wires? You would need to connect up the white wire from the heat lamp to neutral and connect either other to the hot feed in turn and see what happens (does the heat lamp have low and high settings that you could choose only one of given only one pair of wires down to the switch).
 
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