MEP-831A CB indicator works... backwards?

[fb40dash5]

Bought myself an 831A as an occasional small backup generator, and because winter sucks & I wanted a project to dink on. Power hasn't gone out yet (and I don't have a transfer setup installed yet anyway) but it's definitely fulfilling its role as a project very well so far! One of what I figured would be an easy issues was the circuit interrupter indicator a) had a burnt out bulb and b) the lens snapped off the housing when I tried twisting it to make sure someone didn't just have it twisted to blackout. I found a 1/2", 24V LED indicator on Amazon for like $8, and figured that's plenty good enough, I don't need to spend another $50 so I can push it to test.

After consulting the panel wiring diagram in the TM for a good 10 minutes trying to figure out why the old one had 3 wires for a simple light bulb (ohhhhhhhhh, the 3rd wire is the power for when you push to test... duh!) I got reasonably familiar with what was going on there electrically. And between that & checking continuity and voltage on several wires to make sure I had the right ones (further confounded by my current lack of fuel gauge, which is also the indicator's ground point, which I removed as the rocket scientist previous owner had installed a chinesium gauge that wasn't even compatible with the sender) I'm pretty certain I got it wired correctly.

Except... it works... literally backwards. It comes on with the ignition switch, just like the oil pressure light. It stays on once running. It goes out as soon as I close the contactor, and it comes back on if I open it. I even went so far as to be confused at first & thought maybe that was how it was intended to work (it actually makes sense from a light discipline point of view, if you figure that 99.9% of the time you had it running in the field it would have the contactor closed) and started prodding around S5 with my meter, and was unable to find a terminal that had constant +24V with the contactor closed, but no power when the contactor was open. And while I can't swear S5 is working perfectly or wired 100% correctly, I can say I did the troubleshooting steps on the switch earlier (though my contactor wasn't closing at first, long story but it was) and the set does produce power on the lugs.

So I'm really confused by both how exactly that happened, and how to fix it? Unless I rear the wiring diagram screwy, and the wire from S5 is actually what provided power for the push to test feature... in which case I'm really confused since one of the other 2 wires is just a ground (which I'm pretty sure I have wired correctly, since it's an LED and it does illuminate) and the other one runs to the fuel gauge, and I just couldn't imagine why any wires on the fuel gauge would've been dependent on the contactor position?

 

[Dieselmeister]

One guess - Measure the voltage on both sides of the LED to a known good ground and see if you are getting 24 volts to both sides of the LED when it's off. I suspect you are somehow applying power to one side of the led, which is leaking to ground (through something like the contactor coil) on the other side, with the contactor open. When you close the contactor, you now have power on the other side of the LED as well, and the light goes out. (Similar to the Alternator idot lights on the older cars. With the ignition turned on, but the engine off, power would flow through the bulb to the Alternator, illuminating the bulb. When the alternator ran, the bulb would have power on both sides, and the bulb would go out).

 

[Guyfang]

Take off the rear top panel, and look down at K1. Make sure your K1 is connected just like this. Wire 149A on terminal 11. Wire number 100U on terminal 12. Its been a long time since I had a K1 in my hand, but I seem to remember that there is another terminal, (13?) on the K1. You can see it on the schematic, its just not numbered.

 

[fb40dash5]

One guess - Measure the voltage on both sides of the LED to a known good ground and see if you are getting 24 volts to both sides of the LED when it's off.

Lawdy, I think you solved it... kinda!

Haven't had a chance to test it yet, but I was thinking about what you said, and how it's not possible for that to happen the way I have it wired. The + wire goes to the terminal on S5 (which has +24v when the contactor is open) and the - wire, since I don't currently have a fuel gauge installed, is temporarily behind one bolt of the hourmeter along with the other wire it shares a stud with on the gauge, which goes straight to a ground.

But wait a sec... remember I said the 3rd wire goes to the fuel gauge too, but it's constant +24v, and what could that have to do with the contactor, so that must be the power for the push-to-test? I think I have my choice of wires, and which goes to which on the LED, backwards. If I wire the + lead to that wire, and the - lead to the terminal on S5, then when both have +24v (when the contactor is open, when I don't want the indicator lit) I should get nothing... and hopefully when I close the contactor, that terminal will be grounded?

Edit: Well, once I tried, failed, and then remembered to double check the diagram (since I have no fuel gauge, I had the 2 leads at M5-I separated & taped)... there it is. Fuel gauge supplies the indicator with constant +24v, the ground is supplied by S5-2, except that is +24v the rest of the time. Didn't see that coming. Thank you good sir!

 

[kloppk]

Take off the rear top panel, and look down at K1. Make sure your K1 is connected just like this. Wire 149A on terminal 11. Wire number 100U on terminal 12. Its been a long time since I had a K1 in my hand, but I seem to remember that there is another terminal, (13?) on the K1. You can see it on the schematic, its just not numbered.
View attachment 889423

Guy,
That schematic is for an 802/803. OP is working on an 831.

 

[Guyfang]

Overloaded again!! You know what happens to a lame horse!

 

[kloppk]

Bang!