Hey guys, this is my first post here but I have been lurking for a while. I have an 87 MC9 with a 6v92. It was formerly JR's bus. (NJT5047).
Here is my issue. A buddy was helping me put a rebuilt starter in the bus and he wired it wrong. He wired the starter switch wire (red wire) to the ground post on the solenoid that connects to the starter (10g white or yellow wire). I didn't double check his work before we tried starting the bus. :'( When we tried to start the bus we heard a very low hum and then nothing. Tried again and now absolutely nothing happens. I double checked the wire and saw the mistake. I put the starter switch wire on the correct terminal and attempted to start again. The bus does nothing. JR mentioned a relay may have been tripped, but I have searched online and can't figure out where the starter relay is or what to do next.
I appreciate your help! Thanks in advance!
-Mike
Well, first a bit of clarification. Relays don't trip. Circuit breakers trip, and there's not one in the starting circuit unless it's been added.
There is a relay in the starting circuit, and it may be possible you fried it, but I'm skeptical as the starter solenoid wire goes through the contacts,
not the coil.
First, you need to determine if you have voltage on the wire. Assuming you have a multimeter, remove it from the starter and check it for voltage when you hit the starter switch.
If you have voltage, then test the starter negative for continuity to the bus negative. It's possibly you burned out the ground wire.
Also, check the continuity of the solenoid coil.
Make these checks and get back to us.
Thanks for your response and clarifications. As I am sure you can tell I am pretty wet behind the ears when it comes to this stuff, but I'm willing to learn. JR is coming over this afternoon to checkout the starter. He's concerned I still don't have it wired up right. I'll let you know how it goes.
-Mike
Please don't take this wrong, but with electrical there's usually many wrong ways to connect something, but only one right way. The wrong ways often result in smoke, etc.
Happy New Year and welcome to the wonderful world of buses.
Ted.
If the start wire was connected to the ground terminal, when you turned the key, the 12/24v went thru the key switch and relay directly to ground, so you shorted the 12/24v start circuit. I would be looking for a fuse or breaker, if there are none, then You may have burned out the start relay or a wire somewhere, or the key switch. You need a voltmeter to troubleshoot this. Get the wiring corrected and see if there is voltage on the starter solenoid, if not, start looking!!
The starter relay is in the engine bay electrical compartment on the driver's side of the bus, just forward of the side engine bay door. It pulls power from the rear 24v bus bar. It is controlled by the two starter switches (front and rear) which go through the neutral relay to stud 26 in the rear electrical compartment. Put the master switch up front to ON, put a trouble light on stud 26 and toggle the rear start switch. You should see the trouble light go on and off. if it does, put the trouble light on the wire that goes to the starter motor solenoid and toggle the rear start switch, you should see the trouble light go on and off. If it does, the problem is the starter solenoid. If it doesn't, the problem is the starter relay. Schematic is here, page 7-48: http://busconversion101.com/PDF_Files/MCI%209%20Maint%20Manual%20in%20PDF%20format/MC-9%20-%20Maint%20Manual%20Section%207.pdf (http://busconversion101.com/PDF_Files/MCI%209%20Maint%20Manual%20in%20PDF%20format/MC-9%20-%20Maint%20Manual%20Section%207.pdf)
Brian
Absolutely what Brian said. Forget about using a volt meter for this troubleshooting. For high amp circuits a VOM is generally useless as a troubleshooting tool. Use a plain old garden variety test light.
Hey guys, educate me here, obviously, I use a voltmeter cause I have one.....are 24v test lights readily available? I have a 12v one but wasn't sure if the 24v was easy to get, that's why I suggested a voltmeter......which is a good investment if you have a bus, I think.
A lot of test lights are dual rated for 12 and 24. I believe even harbor freight even carries one
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Caterpillar has the best test light on the market for a little over 25 bucks it reads 12 and 24 volts mine has to be over 30 years old and I never had to replace even a bulb
I use the 12v ones for 24v all the time, maybe the bulb doesn't last as long but I just buy a new test light. The one I have now is at least 20 years old, funny how we keep the old tools and after a few decades they get to be the good tools... I pulled out a handsaw the other day to finish some cuts, a nice old Disston cross-cut saw that I had reset and sharpened maybe 30 years ago, and saw my grandfather's initials on the handle. He died in 1967, he probably bought that saw in the 1930's. I honor it and him by using it.
Brian
Well thanks guys, I learn something on this forum every day.
Thanks for all the replies guys! We found a couple of issues. Using the multimeter we found that the ground cable between the solenoid and starter was bad. After fixing that we jumped the positive lead into the solenoid to the starter wire on the solenoid and proved the solenoid and starter were good. Next we used a 12v/24v test light they way Brian suggested. We found a couple of interesting things. The first we found is that the #26 stud was not getting power at all. In fact it only had 1 wire connected to it, so I'm assuming a previous owner has rewired the starting circuit in the back to another stud. Everything checked out ok in the front junction box per the wiring diagrams. Ultimately what we found is that the neutral relay is bad. We could jump across it and start the bus, but it would not engage when providing power to the input terminals directly. We also tested from the starter button on the dash and found everything up to the neutral relay is good.
A lot of lessons learned here for me. I appreciate your replies and patience and I hope I can contribute to this board in the future.
-Mike
Stud 26 is after the neutral relay so if it was bad you would see no power there. Glad you found the problem, it sure wasn't completely obvious and it was a tricky troubleshoot.
Brian
I changed the 12v bulb in a test light to a 24v bulb. I can use it for 12v also, but the light is just dimmer.