Carrier Supra 550 Starting Issue

[ChelseaNY]

Hi All,

I have a supra 550 with a strange issue. When you turn it on, the electric fuel pump engages, you hear the unit buzzing but it never cranks and then the evap fans come on. It will start if you use the manual crank switch next to the relay box or if you jump the starter but it won't start on its own. Checked all relays, fuses and for broken/corroded wires, all seems well. Also swapped cab command, relay board and micro from another unit and it's still doing the same thing.

Any help would be greatly appreciated.

Thanks!

[cadwaladr]

Could be the alternator,because when the alternator starts to charge that's how it knows it's running try searching the field wire to the alternator

[cadwaladr]

Damn spellchecker should read try earthing the field wire at alternator then try to start

[ChelseaNY]

Thank you! Turns out there was a broken wire in the alternator harness that was missed on initial inspection. No idea how it happened considering it looks like it was cut and was pretty deep inside harness...no corrosion or anything... but it's fixed.

Thanks Again.