how to remove the Thomas Vandalock ignition interlock

[c_hasbeen]

The ignition interlock system on school buses is to make sure that the bus will not start if the emergency exits are locked. This is accomplished by two separate circuits wired in series, the first is the ignition interlock that prohibits the starter from engaging; the second is a buzzer that notifies the driver at the driver seat and at the door that has triggered the interlock that a door is locked.
This is to allow access for emergency personnel should there be a need to gain entry from the outside.

The easy way to start this process is:
INTERLOCK REMOVAL
1) Look under your dash at your key ignition switch, there will be a #10 wire it will be black or purple, there will be a smaller wire the same color with a tracer color.

2) open the door to your wiring panel and find those two wires coming in from the front of the bus, this is a large bundle of wires so you may need to remove a couple of ty wraps to find these wires.

3) Trace these wires, the biggest wire will go to a terminal and be fasted with a nut, the smaller wire will go to a relay, either directly or be spliced to a different color wire.

4) Trace the smaller wire to the relay, the relay will have one yellow wire which provides a ground to the relay to allow the starter to work, there will be a jumper wire from one terminal to another and that will have a wire that will lead back to the terminal where the #10 wire is connected, it most likely will be the one above or below the #10 wire

5) Disconnect the wire from the terminal that comes from the relay.

6) Cut the wire going to the relay and crimp a ring terminal to it.
(this is the smaller wire from the key ignition)
7) Connect this new ring connector to the terminal you just removed the wire from the relay.

Test your engine and it will start.

9) Unscrew the relay and disconnect the yellow wire, save the relay in your parts box, these are common use items.

BUZZER REMOVAL

The buzzer works opposite of the interlock, it will activate when it finds a ground, where the interlock looks for a continuous circuit.


1) Find the buzzer, it is right next to the relay you just removed.

2) Remove the power wire from the push on terminal strip just above it.

3) Remove the wires from the other terminal on the buzzer.

4) Unscrew the buzzer

5) Start bus and notice no annoying buzzer

CLEANUP

Once you have removed the relay and the buzzer make sure you pull the wires you disconnected from the buzzer and the relay out of the way maybe put a crimp cap on them or tape the ends to keep them from touching something they should not, then ty wrap them and the big bundle of wires you opened up to find your ignition wires.

Below are some pictures, and a picture of the schematic that is on the door to my engine.

This worked just fine for me, and I believe it is better than trying to disable the interlock at each of the door locations and the buzzer trip points.

thanks
Cliff

[c_hasbeen]

I found a link to a wiring diagram that you can print out if you need

http://www.notagz.com/tbb/0502b.PDF

[VeldatheWonderbus]

Is the screwdriver pointing at a hard start/cold ignition relay in the third picture? And is the (solenoid contractor) relay just outside images 2 and 4 to the left side, mostly shown in image 5, and shown fully in the bottom left of 7 and 8?

Velda has a very similar-numbered relay, 70-111226-5A, but all of the wires connected to it are white. I still have to pull the panel with the ignition switch to see if that has variously-colored wires or if they kept it monochromatic there too...(I'm going to be using a lot of wire labels).

[Tango]

I don't even own a Thomas but wanted to thank you for sharing this info. Really handy knowledge...good on you!

[c_hasbeen]

The first relay is the interlocking relay. The other SoLenoir is one of two, the starting solenoid is the closest to the front it also gives gages and low air buzzer power.
The one in the corner of the second picture is the same part number, it is connected to other electrical body stuff, I believe one of those functions is the fast idle.

[VeldatheWonderbus]

To expand this thread a little, I'm going to add my photos and explanation, as Velda (1999 International Genesis, AmTran build) was set up a little differently than the Thomas system c_hasbeen described above. But it's still similar-enough to keep it in the same thread and not start a redundant one.



In contrast to the Thomas system, the interlock relay in Velda is wired directly to the buss panel terminals from each post (the larger, top-and-bottom posts on the relay), essentially in the location of the jumper between those terminals in the Thomas system. The "ground" terminal on the relay (the little one in the middle) is connected to the emergency exit doors, and will only allow the interlock relay to connect if the doors are unlocked.

I followed c_hasbeen's steps in the original post, but used one of the wires that used to connect a buss terminal to create the jumper to the other terminal. It took a few minutes to see what was different about Velda than the system above, but once I understood that the same components were involved, but in a different order, it was easy to amend the steps above to remove the interlock system.

Here's the result - note that I still haven't removed the relay in this picture; the wires I removed from it have their terminals covered in black electrical tape.



Again, all of this was made a little more interesting by the fact that whoever wired the interlock used a single color of wire for the whole system (whitish pink in the images above), so the black/yellow/purple distinction didn't help me. Hopefully this slightly different explanation of removing this system helps others.

Cheers!

[ism minerals]

Thanks for the info, I will be getting around to this very soon.

[VeldatheWonderbus]

I meant to include this image in my last post, but it slipped my mind. I used c_hasbeen's steps and then drew them out so I could see what I needed to do, step by step. So the numbers in the diagram correspond to his instructions above, which I highly recommend that you print out and have sitting next to you while you're working.

I also watched this video about how the relay itself works, which was quite helpful in simply understanding what I was trying to accomplish.

[YodaBusDog]

My bus 95 international t444e 3800
My wires were pink and the terminal was under the dash
OK so what I did was
1. Find the terminal "wires on terminal 2 pink 1 ground."
2. Take 2 pink wires off
3. Install both wires on one side of terminal.
4. Finished bus started right up.

[zoomy]

Thank you guys, you made my weekend.

https://www.youtube.com/watch?v=KcdQ0_IrA2M

[homeintransit]

I have a 93 transit liner and I disconnected all the exit alarms so now I have the same problem. Everything seems to be the same system except I can't locate the relay that needs to be bypassed. I have the same ignition, same buzzer, same wiring box, but there isn't a relay anywhere I can find.

[VeldatheWonderbus]

All I can say is that if disconnecting the exits resulted in the bus not starting, there's a relay somewhere. Follow the wires until you find it, because you have to disconnect it to get your bus to start again. If the bus is starting, then you're right, there isn't a relay to remove. Good luck!

[Bus Driver]

I am now having this problem. I think it is the interlock, but can't be sure because I don't recall disconnecting any exits to cause the problem. We were taking out wall panels though and who knows, maybe my old man cut a wire someplace.... I did figure a temporary work around that may help anyone in the same boat as me.

I have a rear engine bus that can start at the the engine in the back. It seems unaffected by the interlock (if that is indeed the problem) but this does not let me drive. After some trial and error I figured out if I first put a key in the ignition up front in the "on" (not start) position then that gives me juice to the electric system so stuff like the lights accelerator pedal all work. Then I go to the back and fire up the engine. Voila, I can drive.

Now to figure out the ignition thing. I'm way out of my element with this electric stuff. ��

[superdave]

Originally Posted by Bus Driver

I am now having this problem. I think it is the interlock, but can't be sure because I don't recall disconnecting any exits to cause the problem. We were taking out wall panels though and who knows, maybe my old man cut a wire someplace.... I did figure a temporary work around that may help anyone in the same boat as me.

I have a rear engine bus that can start at the the engine in the back. It seems unaffected by the interlock (if that is indeed the problem) but this does not let me drive. After some trial and error I figured out if I first put a key in the ignition up front in the "on" (not start) position then that gives me juice to the electric system so stuff like the lights accelerator pedal all work. Then I go to the back and fire up the engine. Voila, I can drive.

Now to figure out the ignition thing. I'm way out of my element with this electric stuff. ��

if you have locks on your side door or rear window unlock them. that will kill the bus also. the kids need a way out and the over night locks have to be in the open position. good luck

[Bus Driver]

Yeah, those were the first things I checked. I learned about that quickly after I first got the bus. "Oh nice, this locks..." then the loud buzzing and no starting. After that it just stayed unlocked

The door/window is not locked. Bus won't start, but there is no buzzing alarm either. I'm not sure if that is significant for trouble shooting?

[Versatile]

An oldie but goody thread.

I want to get rid of the switch on the side door. I see i could it is a plunger type switch that i could just wrap with tape but would rather remove it. There are 2 white wires and 2 black wires. Should i do what?

[DWJoyce]

Some of those wires, terminals and such, actually look useful!

[Robin97396]

I'm sure you guys have already seen the videos about how to disable the interlock system on youtube.

To have a functioning interlock system the starter has to have some extra wiring. If you can disconnect the additional wiring from the starter and then follow those electrical leads to your fuse panel you should be able to disable it completely.

The interlock system seems to vary on different buses so each of us has to become a bit of an electrician to disconnect this right. If you disconnect something, stop and try to start your bus before moving on so you can reconnect it if you have any problem starting.

[PDX-Janel]

I have a 2003 Thomas Safe T I Liner rear engine. I can't find the ignition solenoid ANYWHERE. Can anyone help? My relays don't look like any of the pictures I've seen either. Lordy lordy....I need a beer.

Sent from my SM-G935V using Tapatalk

[Genghis]

Cliff, what year is your Skoolie?

Genghis sends.

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