Silverstate55 Posted June 24, 2020 Share Posted June 24, 2020 Truck: 1992 DM690S Engine: E7-250 Transmission: Maxitorque 7-Speed While backing my new-to-me (auction win) 1992 DM690S off of stepdeck trailer, the single air tank on passenger side got hung up on the trailer and broke a couple of air fittings off...the delivery driver was backing the Mack off of trailer and pulled the Emergency Stop lever next to ignition. I quickly bush-fixed the broken fittings and when we tried to restart the truck to finish the removal, there was no power whatsoever. The battery cables were corroded and crap, and the batteries were listed as “Weak - Needs Jump.” I used 2 fresh batteries to initially jump-start the truck before it was backed off of trailer, but when I hooked these up again there was still no power at all. I quickly found the battery cutoff switch that was installed (as I put these on all of my other trucks), and when I ran my multimeter across the terminals it tested fine (open when shut off; closed with no resistance when turned on). I jabbed my MM probes into decent sections of the battery cables to run a quick resistance check, and got reading with nominal resistance. The battery cables will be replaced and the batteries have been load-tested to show that they are all in 100% good condition, but I still can’t get any electrical power whatsoever. I haven’t had a chance to trace out the Emergency Shut Down, is there a switch that needs to be reset somewhere that I haven’t found yet? On older military NHC-250 Cummins motors, the Emergency Shut Down lever needs to be manually reset on the IP before they will restart; does this engine have this type of feature? The truck has been neglected for quite some time and the dash is in pieces with wires everywhere of course...it is possible that a wire has broken off behind the ignition switch....or is there another issue with the the circuit breakers that I should check? Sorry for the rookie questions; I haven’t had time to thoroughly diagnose this issue due to being so busy lately. I’ve tried searching for used repair manuals & schematics but was shocked at the gold-plated prices the few sellers I could find were demanding. Thanks in advance for any advice/help! Quote Link to comment https://www.bigmacktrucks.com/topic/63027-92-dm690s-lost-all-electrical-power/ Share on other sites More sharing options...
Quickfarms Posted June 24, 2020 Share Posted June 24, 2020 That is how you shut the engine off, that is not an emergency shut down.Welcome to Mack’s It’s time to chase wires 1 Quote Link to comment https://www.bigmacktrucks.com/topic/63027-92-dm690s-lost-all-electrical-power/#findComment-454032 Share on other sites More sharing options...
fjh Posted June 24, 2020 Share Posted June 24, 2020 My first thought is the accessory relay if you turn the key on and you don't hear a click in the the dash I would check there first! Quote Link to comment https://www.bigmacktrucks.com/topic/63027-92-dm690s-lost-all-electrical-power/#findComment-454039 Share on other sites More sharing options...
Quickfarms Posted June 24, 2020 Share Posted June 24, 2020 My first thought is the accessory relay if you turn the key on and you don't hear a click in the the dash I would check there first!On my truck that relay only powers the heater and AC Quote Link to comment https://www.bigmacktrucks.com/topic/63027-92-dm690s-lost-all-electrical-power/#findComment-454050 Share on other sites More sharing options...
Silverstate55 Posted June 24, 2020 Author Share Posted June 24, 2020 Thank you all for the helpful replies, I appreciate it and will post my results when I get time to troubleshoot. Great knowledge here, I appreciate your willingness to share and have patience with this Mack Newbie. Quote Link to comment https://www.bigmacktrucks.com/topic/63027-92-dm690s-lost-all-electrical-power/#findComment-454053 Share on other sites More sharing options...
Popular Post Silverstate55 Posted April 20, 2022 Author Popular Post Share Posted April 20, 2022 - - UPDATE - - Found the problem! The solenoid on the exterior of the driver’s side firewall, just below the wiring terminal strips, went bad…when we jumped the terminals, the engine roared to life and had full electrical power. Many thanks to my friend Wes who helped me find the problem. When I replace the bad part, I’ll post a part number and update with pics. 4 Quote Link to comment https://www.bigmacktrucks.com/topic/63027-92-dm690s-lost-all-electrical-power/#findComment-495719 Share on other sites More sharing options...
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