Pulling 12 Volt trailer with 24 Volt bus

[oldmansax]

YEEEEEEAAAAAAA! We are FINALLY buying a bus!    A beautiful 1973 MCI already converted. Now we REALLY need help! This bus still has the original 24V system. I want to pull my 12 volt trailers with it. Both trailers have electric brakes and obviously 12V lights, turn signals etc. I know someone else has already solved this problem. How is it done?  Thanks!!

[Ncbob]

Look in your E-mail box and you'll find a wiring diagram which might help.

Bob

[gumpy]

http://www.gumpydog.com/bus/MC9_WIP/Electrical/Tail_Light_Converter/tail_light_converter.htm

[Jeremy]

The easy answer to this is to put 24v bulbs in your trailer lights. Granted, this is not so easy if you're pulling a toad and using the toad's existing lights as trailer lights, but in the vast majority of cases this solution will work. If you wiill be pulling a number of different trailers, or your trailer gets used behind both 12v and 24v vehicles, then keep a dedicated light board with 24v bulbs in the bus which can be attached to any trailer.

I did this myself and have had no problems - equivalent 24v bulbs were readily available, the indicators (turn signals) still flash at the correct rate, and I am assured there is no problem putting 24v through the cable and wiring intended for 12v.

Jeremy

[Jeremy]

Sorry - just noticed your mention of electric brakes. What on earth are electric brakes? I don't think we have those in the UK

Jeremy

[oldmansax]

Look in your E-mail box and you'll find a wiring diagram which might help.

Bob

Thanks! I was hoping for something easier but relays will work. For for the electric brake & controller. I am thinking about just pulling 12V from the same source as the lights & using that to power the controller & brakes. I guess another 24V relay from the brake lights will serve the activate the controller. What do you think?

[oldmansax]

Sorry - just noticed your mention of electric brakes. What on earth are electric brakes? I don't think we have those in the UK

Jeremy

Thanks anyway Jeremy. All suggestions welcome!! I can't change the bulbs because I pull these trailers with my dually too. One of them has 16 lights so it would be a pain.

Electric brakes are pretty common here in the USA. They are used on a lot of trailers under 10,000 lbs. Basically, they use an electromagnet in the drum to actuate the shoes. The controller (in the cab) regulates the voltage. More voltage, more braking. It is a pretty simple system.....until you are on a single lane highway in the middle of the night & it does not work!

[Hartley]

Run a heavy line fom the 12-volt tap of the batteries to the dash area ( #10 ) wires at least.
Then run one back to the brake terminal on the plug. That one goes on the output of the controller.

If while you are at it you pull and extra wire like a #14 or #16 along with that you can pick up the
12 volt brake light signal from the brake light relay that you hook up for the trailer. That way
you will have the signal for the controller.

I did that on my MC9 and also installed an LED marker light down low on the left instrument panel
that comes on when I have the brakes on. It tells me that there is power to the trailer relays
and whether I have by brakes on or pedal is stuck.

Relays are available in either 12 or 24 volts. I used 12 volt relays with a resistor on the ground leg of each relay
to make it easy to get replacement relays just about anywhere in 12 volt versions. I used a 950 ohm 2-watt
resistor on each relay. I also used automotive standard sockets for the relays. The same sockets and relays
are used on lawn equipment, boats, cars and trucks.