12v headlights in '76 TMC MC8

[windtrader]

Today chased down the confusion on the headlight voltage in my '76 TMC MC8. I only have MCI manuals but they state headlight system is 24v. But the coach has 12v headlights, standard H5001. I noticed a tag on the side instrument panel stating it is 12v headlights.

This MCI bulletin describes the 24-12 conversion but states it started on the MC9. http://www.mcicoach.com/service-support/serinfo/serinfo07G.htm

As shown in the reference page, there is a wire running between the two 12v main start batteries. It has switch on that wire (does not look original) that then heads through a wall into the coach chassis.

I'm wondering if MC8 coaches coming from TCM Rosewell had this conversion done at the factory.

Has anyone heard of TMC specific factory manuals?

[gumpy]

I'm not aware of TMC specific manuals. I believe they were wired to the MCI specs, and I don't think the 12v headlights came out until sometime in the MC9 production. I had a late production MC8 and it was 24v bulbs, if I recall correctly.

If you have the sticker, it probably means it was converted to the MCI bulletin.

Have you tested the voltage at each headlight? It was not uncommon for the headlights on the MC8 to be converted to the 12v system shown in the MCI bulletin. It was also common for mechanics to "re-engineer" the headlight wiring to run directly off the 12v tap. This usually killed the batteries in short order, though. If you haven't checked the voltage at the lights, pull both sides and check the voltage in the sockets. If one reads 24v and the other reads 12v, it's been converted. If they both read 12v, it's been screwed up.

[Dave5Cs]

Don Mine is the same with the same plaque and test as a 12 volt system. Check stud 55 in the front electric panel and see if they are wired to that if that tests as 12 volt. Other wise it will be as Craig says 24 and 12. They just split them.

[bevans6]

My 1980 MC-5c had an MCI supplied conversion kit that consisted of two 24 volt to 12 volt conversion boxes, one for each pair of headlights (left and right).  The box was about 3" by 6" by 1" thick, I don't know what was inside them, located behind each set of headlights.  It did not work well, the 12 volt voltage out was low, and it flickered.  I converted back to 24 volt lights with quartz-halogen bulbs.

[buswarrior]

The conversion kits came with the labels/plaques.

In a mixed fleet, it would be popular to convert the newer coaches, and leave the ones closer to being sold, and the labeling was for the tech to choose the correct replacement bulb.

This way, the date was set, when coach xxxx goes, we're done with 24 volt headlights.

I will echo the importance of unplugging both lights, and finding 24 volts to ground at one light, and 12 volts to ground at the other. You will murder the chassis batteries if you are 12 volt at both lights.

Happy coaching!
Buswarrior