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MR 688 won't start


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This truck will not start with the key switch. You can jump across at the starter/solenoid and it starts. With the key switch in the "start" position I have no power down to the solenoid thats mounted between the cab and the bracket that holds the air filter element. The only power at this solenoid is the big wire that comes from the starter. Is there something simple im missing? With it being an automatic is there something that would not register its in neutral and not let it start?

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Could be several things...bad key switch being one of them. The other option is a bad auto shift cable or neutral safety switch. I have seen them go bad on the Allison autos and prevent starting.

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Barry - Watt's Truck Center Parts Manager and BMT Webmaster...1-888-304-MACK

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The key switch gets a hot post when i turn it to the start position. I trace that wire to where it goes into a four prong female plug that has a relay that plugs into it. I have power into this when turning the switch to the start position, but when i test the other 3 wires that are hooked to this relay i get now power. Not sure what this relay is or why theres no power that comes back out of it, but i put another relay on and still the same problem.

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