Lost all gauges and start button

[gumpy]

So which gauges work and which ones don't?

[Scott & Heather]

Coolant temp works
Speedo works
Air pressure works
Voltmeter dead
Fuel gauge dead
Oil pressure dead


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[lostagain]

Double check and clean up all the grounds. That is where the problem lies more often than not.

JC

[gumpy]

Coolant temp works
Speedo works
Air pressure works
Voltmeter dead
Fuel gauge dead
Oil pressure dead


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I don't see Air Pressure, Voltmeter, or Fuel in the schematic. The oil pressure is in with the speedo and water temp. I was thinking maybe the others were aftermarket and connected differently, but the oil pressure is killing that theory.  Also, both water temp and oil pressure come from the back. Both are attached to an engine block terminal, and both go through a harness connector on the engine side of the rear junction panel. So, potentially there might be a problem in that harness connector, especially if you did recent work in the engine compartment.

Since oil pressure is shown in the schematic I have, I suggest you start with that. From the oil pressure sensor, a wire goes to pin 3 on the block terminal strip. Then it goes to "Pin C" on a harness plug, and continues to stud 34 in the rear junction box. It then goes to stud 1 in the front junction box. It then goes through a connected, probably under the dash and to the gauge. There are 3 terminals on the gauge, ground, 24V, and sense wire described above.

So maybe start there and see if you can find a disconnect in that circuit.

[daddysgirl]

You have a TYPO I think.
If you look just to the left of stud 13, CB says "CC". Directly under that is another CB "CC". I would bet the one following "Z" might be the issue?

[Scott & Heather]

Awesome Craig. I checked everything in the front jbox from the gauges to the studs. Solid connections there. I used a tone generator initially then read the wire labels. So we are good there. Gauges are grounded properly. I'll check the rear jbox and harness. I did zip tie that harness to get it out of the way. It was hanging down. I had no idea my fuel gauge went through that way back there. Thanks so so much Craig for your help. Andrea not a typo that I know of. Two different amperage breakers both involved with the "check bulb" test button circuitry.


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[gumpy]

I would be surprised if the fuel gauge goes through the rear panel, but I don't see it on the schematic.

Are you sure you have 24v to the gauges that are not working?

[Scott & Heather]

I'm confused at this point. A black wire labeled #3 is connected to a stud on each gauge (all three, volts, fuel, oil). I assumed that was the 24v feed. But there isn't 24v going to them at all after checking with my voltmeter. The other stud is sensor, and the other one of curse is ground. I applied 24 volts to the power stud and it did nothing but heat up my jumper wire which I immediately removed. I'm at a loss here. I need to just take some time to look hard at this with my schematic. Thanks so much for trying Craig. at least I know I'm good at the back up to the front. Somewhere in the front, we've lost 24v to the gauges. I'm not sure where the 24v feed for them comes from but that's likely my issue.


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[Lin]

I am a bit vague on what's going on, but since you say that jumping 24v just heated up the wire, would that suggest a short?

[luvrbus]

Start with volt meter when the main switch is on both studs should be hot they tie a lot of gauges into the Volt meter loop

[Dave5Cs]

If it heated up when you touch it with 24volts might be the ground not the power stud. You created a short. Touch the ground probe to the bus body or metal and then touch the positive probe to each stud with key on and see if you have 24 volts on any of the three. Just an idea from a distance. Like Clifford said it may be wired in series to all 24 volt gauges or a few in a row.

[gumpy]

I'm confused at this point. A black wire labeled #3 is connected to a stud on each gauge (all three, volts, fuel, oil). I assumed that was the 24v feed. But there isn't 24v going to them at all after checking with my voltmeter. The other stud is sensor, and the other one of curse is ground. I applied 24 volts to the power stud and it did nothing but heat up my jumper wire which I immediately removed. I'm at a loss here. I need to just take some time to look hard at this with my schematic. Thanks so much for trying Craig. at least I know I'm good at the back up to the front. Somewhere in the front, we've lost 24v to the gauges. I'm not sure where the 24v feed for them comes from but that's likely my issue.

Again, you have a short somewhere that's blowing a circuit breaker.

Wire 3 comes from the master control relay, which is enabled when you turn on the master switch. It goes to stud 14. Check stud 14 for 24v.  From there, it goes to the 6 amp circuit breaker #3. It's probably the one labled CC in your above diagram, but I think it's mislabeled. I can't read the amperage as it appears to be torn there. It's the one next to stud 13 on the stud panel.
See my other post for routing to the power stud and gauges. I think your short has blown the 6A circuit breaker. You'll need to disconnect each of the gauges one at a time, as well as the tell tale lights connected to that feeder until you find the short.

BTW, this circuit also feeds the trailing axle unload, so it does go to the back, so the problem could still be back there. These connections are in FJB stud 28, so you might want to start there. It also feeds the buzzer alarm.

[luvrbus]

I wonder how many wiring schematics MCI had for DDEC equipped buses I don't know how it runs with the check engine light out of the loop and the DDEC is reading oil pressure or it would not run.Gauges are usually easy to trouble shoot with Ohms meter   

[Scott & Heather]

Nothing cliff. Nada. Dead. No voltage. I need to find out where the 24v is supplied for the gauges. Craig just helped me out bigtime by sending me the electrical manual!  Wish me luck team


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[gumpy]

Page 177. Look for FJB stud 14 on the left side of the drawing about half way down from the top, and about 1/4 of the way in from the left. You need to find that 6A circuit breaker that is to the left of stud 14. That's circuit 3 which feeds the gauges.