1978 MCI-8 running light failure

[Dietrichfarms]

Hope for some ideas on what to look at next, after my mci-8 running lights went off. Clearance lights and headlights still operating fine just running lights and license plate lamp out. All bus exterior lights still original 24 volt system. Can't find any wires loose, broken, or etc.

[Lin]

How are they switched?  Are they on the headlight switch, the clearance light switch, or a separate one?

[Dietrichfarms]

They are on the headlight switch.

[Lin]

If that is the original set up, you should be able to check the wiring diagrams to see if there is a separate fuse for the tail lights and license plate.  If that does not yield any results, it will be a matter of tracking down where the fault is.  If there is no current at the fixtures, check the appropriate lug in the rear panel.  If there is current there, the problem is between that panel and the lights.  If there is no current there, check at the front panel.  If there is current there, the problem is between the two panels. If there is current there, the problem is between that panel and the switch.  Whichever area you have narrowed it down to should then be investigated, etc. until you isolate the problem.

A tone generator could be very useful, but is probably not required.  Although there is the possibility that a wire has failed in a harness in an impossible place, that is usually rare.  Most likely it will be an accessible connection.  And don't forget to make sure that each fixture has a good ground and all connections you find are clean and tight.

[expressbus]

Dietrichfarms,

I had half of your problem on my Prevost. Mine was the running lights, in the front bumper, would not turn on. I have an overhead toggle that can be used to turn them on/off but they are wired to only come on with the high beam headlights. Turned out my problem was the ground between the light housing and the bus chassis had failed. The failure was the result of 20 plus years of corrosion. Took the lights off the bus and had them bead blasted and powder coated. Rewired them then spliced the new wire to the old feed. They are working fine right now. I have a new, and larger set to install. To do so I will have to enlarge the bumper openings with a grinder or maybe take them to a shop that has a water cutter.

Good luck getting your running lights back on line.

[DEMOMAN]

Dietrichfarms,

     Do you have a maintenance manual?  If you don't, you need one because they have all of the schematics for the bus and junction box stud layouts you will need to troubleshoot an issue like this.  The manual has very detailed descriptions of everything. 

     I have the same bus you do and have had many electrical issues similar to yours.  36 years of corrosion works wonders!     I can help you out with a manual if you need one.  Just PM me.

DEMOMAN