Good morning to all the old schoolers here... I've got a truck (1978 KW W900A) with a series parallel switch. I replaced it about 4 years ago and I don't use the truck...it's in its resurrection stages and just sits around the yard and gets started and moved periodically to keep it lubed up some. It just started giving me troubles again here the other day and won't crank. I had 3 battery chargers on the 4 batteries for a full day on trickle charge to try and bring them up slowly, and got a little life from them, but not enough to get the motor to spin over. They were new TRP batteries 4 years ago...so they're probably junk by now but I'll isolate them today and test them individually to see which ones if not ALL are junk. Anyway, I want to do away with the SP switch. What's the procedure other than putting a 12V starter in...is there a wiring diagram I can use to rewire the cables to 12V? Thanks in advance...
Might be a 24v alternator
Your alternator will be 12 volt. You will need a 12 volt starter. There is a wire on the S/P switch that engages the starter solenoid and there is a relay in the battery box that engages the S/P switch when the start button is pushed or the key moved to start position that wire needs to be moved from the S/P switch to the relay in the battery box. Remove the S/P switch and the redundant wiring and connect all four batteries in parallel.
Not necessarily because the way it works is the SP switch starts it on 24V and then switches to charge the system on 12V.
Good advice. I know which wires you're talking about too. So I can do that and I'll just swap the jumpers around on the batteries to run parallel. Much appreciated. I knew I had to switch to a 12V starter, and I'll get a new (or most likely reman'd gear-reducted one) starter and get rid of that extra headache. Only thing I'm gonna kinda miss is the way that 24V whirls over when everything is working right, LOL...but it's worth the drop in voltage to not have the aggravation. Thanks again mekanik...
Most were installed on 6v group 4 battery packs to boost amps to a 24v starter, with electricity had always been Increase V then Amps decrease. Modern systems went to group 31 batteries, plenty of amps available so started fine 12v, today's starters with gear reduction drives use even less amperage and spin the motor section faster to spin up a diesel engine with ease. Biggest issues on the older trucks with S/P switches was cables, wrong cable sizes, bad grounds, poor either corroded or loose and toasted connections, allowing batteries to get weak and cooking contacts on random intermittent starts as noted above.
This is a set of 4 group 31's. I put them all in new a few (maybe 4) years ago and I don't think I've spun that starter over with them in it more than 25 times in 4 years due to it being a restored work in progress truck. They're all matched TRP (aftermarket parts from KW,) batteries. I isolated them and tested them separately the other day and one tested BAD. I've had that one bad one on trickle charge for the past 3 days now and just re-tested it and it's showing BAD/REPLACE, so there's no bringing that one back to life. I put a good battery in its place, and it fired right up on the first revolution. Amazing how one weak battery can spoil the stew. I'd had THREE chargers simultaneously running on 2A/6A charge for several days and couldn't get it to even make one round. Put a good battery in the place of that bad one, and it fired off like it was just running a minute ago, after sitting for a month. Still plan to eliminate the SP switch though.
I've no experience with your set up. I am an electrician & I dabble in automotive (truck) stuff. I've had some bad experience with series parallel battery groups. Most common are solar storage & generator storage. I find these systems to be brutal if one battery becomes weaker than the others. If one offers more resistance than the others in a series path, it gets all the charging effort, good batteries get less than needed charge. Once had a system using golf cart batteries, two runs of 3 12 volt batteries. The system was set for 36 volts. It powered lighting & kitchen load for a lodge housed up to 25 college students. No receptacles except kitchen, but each of 8 bedrooms had a snarl of extension cords, and assorted hair dryers. We went crazy trying to keep the place in batteries. You propose eliminating batteries. My first thought is dormant batteries need trickle charging isolated from others. Decouple one cable from each, put a battery tender on each. You'll die of old age before they fail. Batteries HATE dormancy!
It’s fairly straightforward. I converted a bunch of them back in the day. Three or four Group 31’s, a 12v Prestolite, new 2/0 cables and don’t forget to run a ground strap to the frame. Run the S wire that went to the S/P switch to the S terminal on the starter. If you need a wiring diagram, just use a generic one from the Delco Remy Catalog.
Only thing worse was the old Mack's that used a series parallel switch and were positive ground. That **** really makes your head spin sorting out electrical issues.
39mt gear reduction delco will make it spin good. Also alot lighter to lift in.
I've dabbled in heavy trucks with 12 & 24V systems for the past 50 years. I hear what you're saying completely...but I have found over the years that the quality of today's batteries has diminished badly in the automotive/HD truck world anyway. I agree on dormancy being the enemy of batteries...and especially winter dormancy, unless removed and stored in a warmer environment. I have a 2001 John Deere LX 255 riding lawn tractor I bought brand new in 2001. I just replaced that little battery in 2023 after 22 years of service. Since then, I had to replace the replacement batteries twice. They simply just don't build things like they once did. As far as my group 31's in this particular truck I am highlighting, 3 out of 4 still test good and hold their own. There's ONE that refuses to take on a charge now. I have a pile of those around here waiting for scrap prices to come up or use as cores.
100%. Those old 40MT's are getting heavier as the years reel by, lol. I've had good luck with the Delco gear reducted starters. I am on the second one in 8 years in a truck with a Caterpillar 3406B, so I'm not complaining.
That's an understatement, LOL...just positive ground by itself had been the cause of many a man's alcohol introduction.
Amen to that! I DO NOT miss the days of bench pressing a 40MT Delco underneath a truck or crane while trying to get a bolt started in it! I've never been a big guy, and damn I hated those things.
Nothing wrong with a 39MT. I switched to Prestolite from my KW dealer for most popular applications. Brand new, no core charge, less expensive, longer service life, another 10 lbs lighter, smaller, less amp draw and they will yank my crank when it’s 40 below. That’s American forty below, not Canadian forty below. Just kidding, I know it hurts the same.
Before I retired, I started using Mitsubishi starters and alternators, with life averaging 5 years or 500,000. Because those starters lasted longer with auto start/stop running A/C and heating cabs in winter. With a system that has auto start, it's X amount more energizing start ups in a 24 hr period. The Delco 39's were/are good but just don't last as long. * https://www.jittruckparts.com/brand/m/mitsubishi-electric
Interesting. I’ll give those a try.
I've got a 39MT in this current daily running KW (3406B) that I put in 8 years ago...and still spinning it over fine. But now that I just said that, it wouldn't surprise me if it gives up this morning...cuz that's the way it goes....
I've never understood the challenges of positive ground systems. In function they are nearly the same as negative ground. Only issue, you want the spark to originate from the center electrode of the spark plug.
My only experience with a positive ground, was a Lucas Knight nightmare in a Triumph Bonneville 750 and I have had enough of that!
Yeah I agree 100%. I saw something on some show a while back that sort of explained the theory behind positive ground systems...if I recall the main though process was that it didn't corrode as badly as negative ground. I can't confirm that theory, nor do I have the desire to try and recreate it, LOL...
Yes sir. That's what is currently in my daily runner, another restored '78 KW that I redid in 2017 and have been upgrading on ever since. Been good to me, actually exceptionally good as twice in 8 years that it's been performing its job, I ran out of fuel two times just pushing the math a bit too far and both times I ran out and lost prime within 100 feet of the fuel pump I was headed to. I put it in around 3rd gear and ran it on the starter to get up to the pumps both times, lol. If that don't get em, nothing will...but it still keeps cranking that Cat over every day. Impressive for a reman'd starter too. I can't get new ones around here...the suppliers and parts places only offer reman's. I'd much rather pay a little more for new but can't get one locally.
The biggest issue I had with the Delco 39's, was diameter. On a DD15 the starter fits close to block just above pan rail. And there is a bracket that restrains cables bolted to block at same point. To install a Delco many would leave the bracket hanging because of interference of installing the two bolts that secured it. Mitsubishi starter has just a slightly smaller field housing allowing everything to go back to OEM. But along with lasting longer, the price of the MIB starter was 35 bucks cheaper from Freightliner dealer. Those prices noted in that link can be beat by most any Freightliner dealer. Plus I only bought Alliance brand-Freightliners own battery in a group 31HD---I can still buy those from local dealer for roughly $90.00 bucks. And those outlasted any other I tried, about 4 years on average with constant parasitic loss from all the electronics and items being powered in sleeper like TV's, coolers, micro waves. * I think I was paying $280.00 for new Mitsubishi starters at that time and the Delco's were $315.00.