Silverstate55

- - 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.

I haven’t had a chance to do anything yet on my DM690S; been working on a friend’s 1979 DM600 water truck and trying to set up my workshop. But I’d like to get it running & install water pump/sprayers before summer & fire season hit.

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.

I will definitely post progress pics...I’m actually pretty excited about this truck and its potential. Thank you!

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!

Hello everyone, Recently had my first Mack truck delivered from the Midwest; it’s a 1992 Mack DM690S...looks to have been a cement mixer at one time, and then converted into a water tender. Has a double frame, camelback suspension, E7-250 engine & 7-speed transmission. The water tanker body is older than the truck, but doesn’t appear to have any leaks. Of course the pump and all spray attachments have been removed. I bought it to use around our farm property here in Utah, but I like it so much that it will undoubtedly get fixed up quite a bit...already looking at some salvage chassis to convert it to 6x6 and swap in some Budd or hub-piloted standard hubs instead of the Dayton spiders (not a fan, sorry). It sold at auction for such a low price it was too good to pass up. One modification it will definitely receive is to mount a 500-gallon diesel tank between the cab & water tanker, so it will fill some much-needed voids in our farm vehicle lineup. For its age, it has low miles (less than 190k) and needs some TLC (fluid changes & flushes, filters, lube job, etc...). The air dryer absolutely needs a rebuild and I’ll probably start by replacing all the air lines, flushing the air tank (it only has one at the moment), adding several separate air tanks to split braking system into primary & secondary along with PPVs and check valves....also need to add gladhands front & rear. Anyway thanks for letting me join on here; I am well-versed in Detroits, Cummins, some Cat motors, heavy equipment & truck repair, but I’m new to Macks. I’ve been reading through some of the tech forums and this seems like a good group of helpful folks with great knowledge.