# Specific 3D Printers, Scanners, & Hardware > RepRap Format Printer Forum > Firmware Enhancements to Marlin >  heater pin numbers

## ohms

Hi, I was installing the e3d hotend with a new heater cartridge and thermocouple. I think I accidentally changed the pin number for #define HEATER_0_PIN. I have it set to 8 right now. is this correct? the hotend is not heating up right now. thermocouple is working fine and I checked the resistance on the cartridge came out to 6.7. 

Thanks

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## printbus

Not sure what you have for hardware or firmware, but I believe the typical Marlin/RAMPS config is as follows:

HEATER_BED_PIN    8
HEATER_1_PIN        9
HEATER_0_PIN       10

It can be tricky to work through the #if #else #endif logic. Always check to make sure no more than one definition is assigned to any pin for your specified motherboard type.

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## ohms

it is a rambo 1.2b board with marlin firmware. Forgot to include that in there.

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## printbus

> it is a rambo 1.2b board with marlin firmware. Forgot to include that in there.


Then I believe the mapping should be as follows:

HEATER_BED_PIN   3
HEATER_1_PIN    7
HEATER_0_PIN    9

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## ohms

ahh pin 9 did the trick. Thanks

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