2000 Mack RD 688 Starter issue

[cfd511]

Kinda have a weird issue going on. One of my drivers called me and said the truck shut down and smoke coming from hood. Upon inspection realized the starter fried. We put a new starter in and few hours later the starter went again. After this we realized there's a short somewhere so we took the old battery box off the truck which had four batteries in it . We wanted to put a passenger fuel tank on that I had sitting around anyway. We pulled all the battery cables out of it and found a shaved wires we were like awesome we found the problem.   we are going to go to two batteries and move battery box. We got new starter in and once again we realize that started is staying engaged somehow. the first time it was really noticeably because it was making noise. so we shut truck down and you can hear the starter slowing down from spinning. after that we kept testing and when you shut truck down you hear the started wind down. we tested the solenoid on the fire wall and the ignition wire has no power until you turn the key . when you let go off key to run the power turns off. it down think the starter is getting power and trying to start . I think its just not releasing so its staying engaged. any help with this.

[fjh]

Check both big poles on the solenoid should have power on one and not on the other! Also is the power wire touching the trigger wire on the starter?

[Vladislav]

Your starter engages electrically. If mechanically that would be solved by the 1st swap. To light up the starter it needs power to its small terminal on the pull relay (on the starter not on the firewall). The sequence is you switch the ignishion in the cab and power goes to the firewall relay. It switches up powering up the starter pull relay. The latter connects its big terminals supplying power from the top one (which is constantly connected with battery plus) to the lower one which is a pole of the starter motor. And also moves the Bendix clutch into the flywheel gear.

In your situation there must be power at the small terminal on the starter pull relay. At the time you turn the key to the starting position but than later on too. The most probably the firewall relay switches on but doesn't switch off once the key in the ingition lock released. Ot the lock itself keeps on regardless you released the key. You pointed you have checked that but may worth to double check.

Overall pretty simple design so just figuring and step by step testing is required.