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Originally Posted by Stormravyn
Hi guys, I'm new here, but have been lurking for a while. Now I seem to need advice lol. I am buying a 1997, Thomas International 3800 with a DT466E diesel in it. This bus has been running fine, then we made the long trek up to her yesterday and she wouldn't start.
Now, I know WHERE the problem is, as my Dad had an old Satellite Sebring that this thing would go out on him every few months, so he kept a handful of them in his glove compartment lol. It's cheap, but without it, the vehicle won't start and you think you have a bad battery connection or even a low battery. But I can't remember the name! So here is WHERE it is 
Driver's side, side access panel beneath the driver's side window. LOOKS like a starter relay, ignition relay, etc but all my searches are saying those are on the engine, firewall, etc and I cannot for the life of me find ANY diagrams, pictures, and labels that tell me not only what all those switches DO, but also the other components under there. The solenoid should be on the starter itself, correct?
What it DOES (and the battery is charged) is... when you turn the key to start it, you hear a ...not really a click as this is louder, deeper and meatier than a girly little click lol. It's more like a clunk but comes EXACTLY from that round, metal device attacked under the access panel that has... oh God if I can remember... 2 red and a black wire (I THINK) going to it. You can FEEL the click/clunk sound every time you turn the key. It's frustrating to not remember what it is. It's an easy switch and cheap, but I have to remember what it is called, as I in no way trust auto parts stores. I may be female but I drove trucks coast to coast over 20 years and always worked on my own cars and trucks etc and KNOW better than to assume they have a clue what you are talking about lol.
As an aside, I will mention that this mounts on its side, right up next to the outer wall, is maybe 6 inches in length, maybe 2, 2 1/2 inches across and the wires connect on the end facing the passenger area. So it attaches parallel with the outer wall of the bus.
Can anyone help, and does anyone know where to get a nice color picture of that access panel inside and out with everything labeled? Thank you all in advance. Her name is Zerah and she is to be our home, so I need to do this right.   |
Several people have identified the mystery part in question as a solenoid. Every solenoid will have a minimum of three wires, two of which will usually be much larger than the third.
The two big wires carry juice from the battery to whatever is being powered, whether it is the starter or the body or to a wheel chair lift. A solenoid is used whenever a large amount of juice is being stopped and started on a signal. Without a solenoid all of the juice would have to go through the switch which would require every switch to be heavy enough to carry the full load--an expensive option most vehicle OEM's won't do.
The smaller wire carries the signal from a switch to activate the circuit. Most of the time the signal comes from the key switch and needs relatively little juice to activate the electromagnet that will close the switch inside the solenoid to complete the circuit providing juice to the large user.
On many buses there will be a solenoid to operate the solenoid on the starter. The starter will look like a typical GM Delco-Remy starter but it will be much larger and will require a much larger starter solenoid to get the starter turning. By using a solenoid to power up the starter solenoid you are able use a very low power switch to turn on a high power switch that will turn on a really high power switch. The signal wire to the first solenoid will most likely be a 14 ga wire, the signal wire to the starter solenoid will most likely be a 4 ga wire, and the power wire to the starter will be 00 or 000 ga wire.
On the first solenoid the power side will always have power unless there is a battery disconnect switch somewhere in the system. If you turn on the key and lights and buzzers are going off the power side will have power whether the key is on or not. A starter solenoid signal wire will only have power when the key is in the start position. When the signal is activated you should have power on the powered side of the solenoid.
A test light is the best tool for figuring out what might be going on with your starter circuit. The light should light on the input side all the time. The light should light on the signal side whenever the key is in the correct position. The light should light on the output side whenever the key is in the correct position. If the light doesn't light up on any of the terminals you have a juice supply problem upstream between the battery and the solenoid--a broken wire or a blown fuse/circuit breaker. If you don't have juice at the signal wire the problem is upstream between the solenoid and the key switch--a broken wire, a wire loose on the terminal on the solenoid or key switch, or a bad switch. If you don't have power on the outlet side of the solenoid when the signal has juice then the solenoid is bad. If you do have juice downstream from the solenoid then you know the problem is between the solenoid and the starter.
To test your conclusions if you have juice to the input side use a jumper wire (don't ruin a screw driver trying to jump stuff on a bus--the amperage can really melt a screwdriver quickly) to the signal terminal. If it makes things work you know the problem is in the signal. If you jump across the solenoid from the input to the outlet side it should spin the starter without using the signal. This one you definitely want to use something besides a screwdriver as it has some serious amperage going through those big wires. If jumping across the input and output makes the starter spin then you know the signal isn't getting juice or the solenoid is bad. If jumping across the input and output doesn't work then you know the problem is downstream between the starter and the solenoid.
If you get juice going out of the output and the starter is not spinning then the problem is somewhere between the battery and the starter/starter solenoid.
Or it could be that the bus is somehow not in neutral and the neutral safety switch is not allowing a signal to go down to the starter solenoid to make the starter spin.
In other words, particularly if the transmission control is not an electronically controlled shifter, double check you really are in neutral.
Also, your bus may have emergency doors/exits that may have a safety switch that will not allow the starter to engage if the vandal/inside door locks are still locked.
Good luck and keep us posted as to your progress!
Good luck and let us know how you are proceeding.
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