MC9 Instrument panel lights need help!

[plyonsMC9]

Greetings bus nuts! 

My instrument panel lights ( not dash lights ) seem to have completely failed.  I "thought" three of the bulbs worked.  Then one.  My first thought was that they were burning out.  Well, then I tested the contacts on the bulb / lamp holders with the clearance lights on and rheostat fully on.  No power. I am assuming this is 24v?  This looks like the original dash lighting equipment.   ( pls see pic below ).

The wiring harness looks somewhat complex to me.  I have a 1987 manual which shows this assembly and it looks fairly accurate. 

The second picture is the back of the panel, with the instrument panel dimmer on the r.h. side.  Wire is disconnected.  I cannot discern the purpose of the disconnected wire and whether that is relevant.

What kinds  of things can go wrong in this area?  Is that a bad question?  Are there alternate, simple solutions to get light behind that panel which have worked well?

Suggestions are definitely welcome!  I'd like to get some light on the subject before travelling to Kentucky next weekend.

Thanks bus nuts! Kind Regards,

Phil

[Tom Y]

Phil, Not much to them. I have an extra panel and will look to see if that extra term is used. You should have a breaker feeding the switch, is it hot?  Tom Y

[plyonsMC9]

Thanks for the encouragement Tom!  After reading your response I went back to the panel with my trusty ohmeter and wiring diagrams.  Turned out, I was doing one of my usual bonehead moves.      When the instrument panel is removed, it no longer is grounded.      So, my testing results from earlier were all wrong.  I jumpered the aluminum instrument panel to the metal bar it is normally mated to, and was able to get a ground and 2 of the 10 or so instrument panel lights to work.    Current from the breaker is good, as is output from the rheostat.    I've found a couple of sockets which don't seem to work, and a few more of the 24v bayonet type bulbs which are dead.  Maybe I could wire a couple of the newer 12v LED lights in series together to provide more illumination to the panel instead of the older 24v light bulbs with the green rubber covers. 

Side note - 24 volt and 16 guage wiring can still produce a very large spark.      

Best Regards, Phil   

[gumpy]

Phil,

Here's an idea that I used....

Take the old blown out 24V bulbs, break off the glass, clean out the brass, drill a tiny hole in the lead connection button, and install a white LED with resistor soldered to one leg. Put the free LED leg through the lead button that you drilled and solder. Clean up with a small file. Bend the resistor to fit over the lip of the brass case and solder to the case. You could fill with epoxy, but it's not necessary
if you make sure the leads are not touching. Be careful installing into the sockets so as not to bend anything and cause a short.

I've been running these in my dash for about 3 years now, and love them. intending on making more for the side panel when I remember to take time to do it.

Oh, by the way, these won't work on some of your warning lights that require resistance to work.  They work on high beam TT, turn signal TT, etc.

craig

[Dallas]

Phil,
You may be well served to provide a permanent ground to your panels.

I had a lot of weird gauge readings until I added a dedicated ground wire from the bus ground terminal in the electrical breaker panel to the different panels. Now I get accurate readings all the time, which usually makes me a mucher happier camper.

Dallas

[plyons]

Thanks guys!  Both are excellent suggestions.  I will follow up on both.  Craig - very creative with that modified 24v bulb setup.    Never would have thought of that one.  Dallas - so true - as I was troubleshooting, in the back of my mind I was thinking "as well as everything is put together in this bus, certainly they aren't relying on this panel cover for a ground".  Wrong!

Best Regards, Phil