Itinerant Air-Cooled

My alternator light wasn't lighting during start up so I replaced the bulb. Now that I have a working bulb I see that it stays on all the time even though my voltmeter shows a healthy 13.5v with engine running. But not only does my alt light stay lit now the EGR light is lit and if I unplug the EGR light the alt light goes out also. Conversely if I unplug the alt light then the EGR goes out. Thinking if I unplug the egr timer maybe that would eliminate the problem I found that unplugging it turned both lights off and if I plugged the timer plug back in both lights came on. I'm wondering if I have two problems, the first with the alt light not functioning during the starting cycle and second a short or something causing the egr light to light up or if they are both related. Electrical woes really confuse me. I need help.

I have a shorted-diode-in-the-EGR-box theory, but I can't quite reconcile how taking either bulb out could "fix" the problem.

If you'll humor me, take a small jewelers-type screwdriver and push the reset button on your EGR box. It takes more force than you think, but you'll feel it click when you get it. Then, do the lights behave normally?

At about 3:00AM I'm laying awake mulling this over and I think exactly the same thing. This morning I went out and reset the box but no change in the behavior resulted. So am I correct that the Alt light should glow during the starting cycle then goes out once the charging cycle kicks in?

All three lights (ALT, OIL, EGR) should come on with key 'on'. This is for you to verify that your bulbs are good. After engine start, all three should go off. The oil pressure light extinguishes because the oil pressure sender opens the ground connection for the lamp when oil pressure exists. The ALT and EGR light extinguish when there is voltage present (and therefore no ground connection) on the blue wire coming from the voltage regulator thus indicating the alternator is working correctly. A long-winded explanation of "yes, you're correct".

Since our first stab went wide, I'll now suggest that you poketh thy head back under your dash (the original scene of the crime) and make sure the blue wire hooked to your ALT light is as it should be (not shorting against anything metal, etc.). Follow it back as far as you can as there are junctions where the EGR key-on-check circuit tee's into that blue wire on the way back to the voltage regulator. If all checks good up front, go back in the engine compartment and check the other end of that blue wire which will be in the plug that connects to your voltage regulator.

If you're positive your alternator is doing its thang, then the only other explanation is the blue wire is grounded somewhere. I still don't get how replacing the ALT bulb started all of this. Are you sure you have the correct bulb in the socket? I suppose if the wrong bulb was in there (ie too physically large), it could be grounding out while in the socket... or sumpin'.

check the power wire to your dash cluster from the fuse box. if its a weak connection, the dash lights and fuel gauge can get a little wonky. Remember that power flowing back from the alternator is what causes the alt idiot to go out. well, the dash can take power from that end of the circuit too! when the current flows through the idiot light to supply the dash lights it turns on the alt light.

Unplug the blue wire from the regulator, does the light stay on? Like dubyah said, check to be sure you are getting a good 12v at the light fixture, and you are not grounding out somewhere between the dash and the reg. Do you have a spare reg, or can you borrow one to test?

Check the two voltages at both sides of the idiot lamp.

1_When at rest ( ignition key not in ) there should be 0v on both sides; lamp off
2_When key is in at first position before starting there should be 0v on one side and 12v on the other side; lamp on.
3_When motor is started and alternator has kicked in ( is primed ) there should be 12v on both sides; lamp off.

I hope this will help locate where the fault is.

RussellK wrote:At about 3:00AM I'm laying awake mulling this over and I think exactly the same thing. This morning I went out and reset the box but no change in the behavior resulted. So am I correct that the Alt light should glow during the starting cycle then goes out once the charging cycle kicks in?

I had the same problem, Russell, a couple of days ago.

The cure was to unplug, clean the little tabs, and reseat each idiot light. They are getting *battery voltage* through the little tab that contacts the plate where the lamp sockets seat. As you do this, you can see a *black* wire that plugs into the whole plate. This is your battery voltage wire supplied via the ignition switch.
Colin

Thanks for the help everyone. The first thing I did was take the light sockets and made sure all the little metal parts were clean and lined up properly. That's when I noticed one of the flimsy little light bulp wires was bent a bit to the side and not wrapped around the base. Got it all back together and started up the bus. Only the egr and oil light lit up. The oil light went out as it should but the egr stayed on. Checked the reset button on the egr timer and it was pushed in. Then I tracked the blue wire under the dashmaking sure everything had clean contact and there were no shorts or breaks. Went around back, checked at the regulator and cleaned up those connections. Started up the bus and there I had an oil light, an alternator light and an egr light all lit up. After a couple of seconds the oil light and alt light went out but the egr stayed lit. So I unplugged the egr timer and the light went out. Thats where I left it. Dick referred to a possible bad diode in the timer. How I would test for that?

Good moves.
I think your bus can live with an un-plugged EGR timer, since it is only a reminder that has no other function.
My bus from Chicago had an EGR but no timer. In France, I tried to maintain it, then I removed it all ( EGR and afterburner ); These do not exist on Europeen buses ).
Double check wether the EGR timer is really needed ( may be for inspections ).

RussellK wrote:Dick referred to a possible bad diode in the timer.

The bad diode I referred to would keep your alternator light lit. Since the oil and alternator light work correctly now, the diode is fine and the problem is the reset switch in your EGR timer box hasn't reset. I know you pushed the button, but it really takes a good push. You can test to see if your pushing is successful by putting your ohm meter on the connections on the EGR box where the blue/green and brown wires would connect (box unplugged). You should read open or infinite ohms. If zero or close, your button isn't pushed completely. You can also disassemble the EGR box and see what's what inside and why the switch isn't resetting.