Toad wiring

[Bill DeGroot]

I have an MC-9 and am planning to tow a 2002 Trailblazer. My plan is to install an additional bulb/socket in the toad's taillights and hook this to the coach's tail/brake/turn lights. Is this feasible, and, if so, can one bulb handle feeds from three different sources. Any help with the wiring diagram will be appreciated.

[NJT5047]

If you can find a leakproof way of intalling two dual filament bulbs inside your existing tailights , it'll work.  One bulb won't do an MC9 (see way below for exception).   If you want brakes, turn sigs, and tail, you gotta have five wires to the tailights and three filaments on each side. 
I installed a set of lights with two bulbs in each light on the hitch.  Which accomplished a legal, simple 24v toad light system, without screwing with the Jeep lighting system...which can cause problems. 
The wiring is simple enough.  Just copy the typical wiring colors for an RV 7 pin to the rear of the toad.  The wiring inputs can be picked up at the tailights on the bus...the LH TS, brakes, and tail can be wired into the harness on the LH side of the coach...you will probably find it easier to get the RH TS at the RH side turn signal.  The RH TS crosses over the rear of the bus, but to access the wire you'll have to cut into the main chassis harness above the engine doors. 
Once you have it wired, just match the correct leads to the lights you are using.  Keep in mind that 24V dual filament bulbs are reversed from 1157 12V.  They are interchangeable, but the 30 cp (bright brake and TS filament) is where the tailight filament is in an 1157.    Ax me how I know this! 
You may also want to consider an RV wiring adaptor on the toad, which taps into the toad factory wiring harness, and converting the 24 to 12V.  You'll have to have 12V DC in the engine room to do this.  If you have a DDEC engine, you have 12 in the rear Junction box, if not..."some assembly required"...you'll have to run 12V to the engine room.   This isn't as complicated as it sounds.  The AC box has twelve volts...and there are unused leads between the front Junction box and Rear Junction box.  ID these unused leads and put them into service as a dedicated 12V DC lead for your relay circuits.  Be careful that you don't cut into anything that's necessay for bus function. 
Mine works fine...looks sorta different with two extra taillights on the hitch.  It is simple and doesn't interfere with the Jeep wiring at all. 
One the other hand, with a 24V system, if you wish to tow anything else...trailer or whatever, you'll have to rewire the trailer (remember the reversed 24V bulb filaments) or add "toad" magnetic lights to the unit.  That's the downside to 24V toad lights.  I don't pull anything else...so not a problem.   
A converter box is doable, just have to have a 24V relay for each circuit you wish to power....LH TS, RH TS, tail, brake, would require 4, 24V relays....and a smattering of wiring knowledge.  The relays should be boxed in a weatherproof container. 
It ain't never simple!  My system is simple...but I didn't know that the 24 V filaments were reversed, so it looked like a bad ground to me...not!   After essentially disassembling the wiring connectors, I saw what was happening.   Simple after that. 
One other possiblilty, is if you convert to 12V, you could buy a "prlority" box and use two bulbs for all functions.   Someone may build a 24V priority box.  I'm not familiar with such an item....it probably exists...there are guys that post on this site that could easily build a 24V priority box.
Hope this helps!  JR
BTW, where do you live?  Perhaps someone could show you how this would work?  Come on up to Timmonsville ,SC   Exit 150 off of I-95
Be lots of good help there.  Free help.  If any specific questions, ask away.  the Doktor will be out for a weekend, but I will return as best my minimal knowledge base allows. 

[Bill DeGroot]

JR,

Thanks very much for your reply and insight. I'm in the process of trying to find sockets that will work with 24V bulbs. There are 12V sockets but they are designed for the 1157 bulb with its offset "pins". If you have any information on possible sources, I would appreciate it. BTW, I'm in northern Wisconsin, a long drive to Timmonsville. If I can't find the sockets, I may have to go the same route you did. Where did you get the lights that you mounted on the hitch?

Thanks, again, for your help.

[NJT5047]

The 1157 style socket will work with the correct 24 V bulbs.   What you have is 1638.  It won't work.  A 1638 is an equal pin turn signal bulb.  It will install either way.   They have dual filaments, but are not separated....both filaments work together.  A 1638 is used in a 1002 style socket.  Not what you are after.
Take an 1157 to NAPA and tell them you want  a bulb similar to the 1157 for a 24V system.   They have them...for $10 bucks apiece.   I believe they are 1663...but not sure.  Someone may know.  NAPA knows.  I bought the lights from NAPA because they had them in stock. 
BK may also know number for a dual filament/dual circuit 24 V bulb.
These bulbs are not used on buses...probably trucks use them in the tractor taillights.
I am using two boat trailer lights on my Jeep for toad lights.  The original sockest worked fine...just had to reverse the tail and turn/brake light leads.   Keep in mind that you'll need another bulb (the 1638 that you have would work fine for the third light...the socket for a 1638  is similar to a boat stern light or some auto dome lights) for either the brake or turn sig
JR.   

[Bill DeGroot]

JR,
Thanks again for your reply and sorry I didn't respond sooner, but I've been gone all week. I did find sockets at partsamerica.com. I ordered the ones that fit the 1157 bulb and have a ground tab. I also found the equivalent 24v bulbs at bulbs.com-1662 for $.89 each.
Bill

[gumpy]

I just don't get it. All you guys go to all this trouble to find all these obscure parts and then try to make them fit into your tail lights so you can run 24 volt bulbs back there, and in the end, it doesn't save you a thing. Maybe a bit of money. Certainly not any time or effort.

Building a relay based converter is simple. I made one yesterday. Took me about 2 hours to wire it up after the components were installed on the board, but I've done several of them in the past. I'd expect a novice to need about 4 hours.
MCI 8-pin relays cost $11, bases are about $4. You need 4 each. With some effort you could find some DPDT relays that are cheaper, but I like to use the same relays the bus has in it so you only have to carry one spare.
Circuit breakers are about 2.50 each. You need 3.
Diodes in the toad wiring to prevent back feeding into the computer cost about $10 each, you need 3.
You have to run the wiring anyway. A 6 prong female trailer connector on the front bumper is about $5. One on the bus is the same. A cord with two male connectors to go between is another $5. You're probably going to put these on for your system, anyway.

Did I miss anything.

Oh yeah, if you ever want to tow a trailer or another vehicle with your system, you're out of luck till you "convert" it's light sockets, too. With a relay based converter, you just hook up and go! I had to pull a U-Haul trailer back from CO this summer. All I had to do was make up a 4-prong converter to go between my bus connector and the trailer. The only way it could have been easier is if I had brought my store bought 6-prong to 4-prong converter that was home in the truck.

I guess using it's still not as cheap as hanging magnetic mounted lights on the bumper, but it's a heck of a lot easier once it's installed. Cleaner, too.

Oh well, that's why this is such an independent hobby. To each his own.

craig

[NJT5047]

Did I miss anything.

Yeah you missed something...please post a simple, easy to follow diagram, parts list....or better yet, how much is two hours of your time worth..Plus parts and shipping of course?     I may want one of your converters. 
I saw Jack Conrad's unit in T'ville...take more than my knowledge to make that thing and make it work. 
However, doing the way I did didn't require any special parts.  All it took was some standard boat trailer lights and 4, 24V bulbs.  This is "simple"...but obviously has it's limits.  My Cherokee has a lighting fault system in the ECM, and several expensive ECM failures have been attributed (perhaps erroneously?) to toad light wiring.  I know some Jeeps with lighting taps are working without problems too.   Just don't know what's causing the problems.   
A Cherokee XJ doesn't have room in the tailight housing for additional bulbs...but a couple of diodes in the OEM wiring could solve this problem too...if I go to 12V system.   
Well.  Lunch is over...got to go finish my block heater install.   Got 3 more gallons of water to complete.  Not leaking. That's good news. 
How soon before you post the diagram?   As I think about it, either Marc or Buswarrior posted a similar system recently? 
JR   

[gumpy]

Well, as for the schematic and photos of the unit being built, see http://www.gumpydog.com/bus/MC9_WIP/Electrical/Tail_Light_Converter/tail_light_converter.htm
The part numbers for the relays and bases are on the page. The circuit breakers and stud connector can be acquired from Waytek. Maybe I'll update the page to put those on there, also.

Note, the photo shows one with all the outputs connected. All you really need is the bottom three on the schematic, with the brakes and turn signals combined, so you only need 3 circuit breakers, not 6 as shown.

As for getting me to make one, you'll have to contact me offline. I don't make these to sell (which is why I provide the schematic for free), but have been known to make up a few for friends. I'm starting to get my son to wire them up, and consequently there's some profit built in to the price, over and above the cost of the components, so he can earn some spending cash since he doesn't have a job (Dad says his school comes first  ).

[NJT5047]

Thanks Craig...I'm going to look right now.  My experience with this sort of thing (I just hooked up my cruise control, and while the components are not expensive, I'll have to make ten trips to get everything compatible..or something) has been that I spend waay too much time and money on some things.   You may... your son may save me money.
Just installed a block heater in my 6V92...the heater fit fine, but stuff all around it didn't.  The dipstick was right where the heater outlet is mounted.  Cool.  This is the way many things seem to end up.  That's now done.  On to other things.  Of course now I've gotta drive across Charlotte tomorrow for more DD anti freeze, or find something locally that's compatible with the red stuff that DD sells??  Monroe doesn't have major offerings in this product.
Just won a bid on some air horns on Ebay.  Cannot believe what some of those things are going for....bid on a set of Mack truck air horns and they ended up at $130 bucks.   I let that one go a $120.  Bought another set for $73.  Grover horns...same as the others that I bid on.   
I'll contact you.
Best, JR