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ClaytonH729, Mechanic
Category: Medium and Heavy Trucks
Satisfied Customers: 755
Experience:  Expert in Freightliner trucks, From the Engine, to the taillights. Hit me with the most complex electrical problem also
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I have a 2005 Freightliner Columbia. On the starter selnoid

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I have a 2005 Freightliner Columbia. On the starter selnoid on the firewall, one of the small wires at the plug is hot all the time?? Should this only be hot when the key switch is ingaged?? Would anyone have a wiring diagram for the starting system on this truck??

Hi, Welcome to Just Answer, I can help you.

You solenoid on the fire wall probably has 3 wires, sometimes 4. The heavier wires go to the solenoid on the starter, the little wires are the ground, and the ignition crank signal to activate the solenoid(Mag switch is what freightliner calls it). One of the hot wires will always be hot then on the 2nd larger post, when you go to crank it, it activates the mag switch and the other post should be hot.

Check power to the signal wire on the Starter solenoid that is mounted on the starter while you have somebody crank it. If you get power there, check your batteries and your cables. 1 bad battery can affect all of them. You can also jump across the larger poles on the mag switch and the starter should crank if your voltage is good enough. If you just hear the starter engage, but won't crank, then most likely your starter is bad. If you hear the solenoid on the starter sound like a ratchet, then you have low voltage and I would check batteries or cables.
Customer: replied 5 years ago.

My problem is that one of the little wires to the solenoid is always hot, I do not beleive it should always be hot, only when the key swith is initaited. One is a ground and one is hot, but should not be hot all the time. So something in the dash, a relay or something is wrong for the wire to be continously hot??

Circuit 15A should be hot only during cranking, what are you using to check this with?
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