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Rob Talbot (12.202.162.5)

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Posted on Friday, October 08, 2004 - 11:27 pm:   

I am obviously an amateur electrician and hope I can describe my problem well enough to get some of your wisdom. We have a nice trip planned in a couple of weeks and I need my headlights!

I am converting the 24 V headlights to 12V after one of my beams went bad. I didn't want to get stranded without a 24 v beam available.

I was told by a electrical engineer busnut to run 12v from my house batteries and replace the 24v lead input at the dimmer switch. Of course . .. new 12v beams too. I read about this on old posts on this sight before starting.

Obviously this isn't right. I have to have a toggle swich to run the power to and then it goes to the dimmer.

What is confusing me is that when the 12v power goes to the switch it runs the highs only and the lows do not come on. (Even when I jump directly to the beam with 12 v power the low beam does not come on.)

When I got to looking at the dimmer switch I saw that it has two wires going to the input (one goes to the relay and the other was 24v hot) and only one of the two sides of the dimmer was hooked up. Even the high beams would not light up without both 12v hot (in place of 24v hot) and the wire (I think it is #34) that goes to the relay hooked up together on the input of the dimmer.

Below the electrical panels at the lower exterior access door I found where the wires come down and then split off. I also saw a thin long tube that says something about OHM's on it. Even jumping power to the wire connections down there I can get all high beams on, but no low beams. I can see that the green #52 wire is the one that is (and was not before when the high and low beams worked on 24v) not connected at the dimmer or down at the lower access. Even so, in jumping the wire with power down below I should have gotten low beams shouldn't I?

Here are my questions:
A. what does the headlight relay do or needed for?

B. I thought the wiring would be power to 1.) a switch to 2.) dimmer to 3.) headlights. Can I wire it this simple way (above) with 12v and what am I missing about my low beams too!

C. Are there any more supplies I need?

D. Can I use the old 24v headlight toggle switch that has 4 leads on it instead of getting a new one?

E. What is the thin long OHM's tube for?

Also: I tested the dimmer and it works.
Buswarrior (Buswarrior) (64.229.209.200)

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Posted on Saturday, October 09, 2004 - 7:08 am:   

Hello Rob

First, you cannot trust that the wiring in your coach hasn't been "reworked" into some unorthodox set-up.

Perhaps the original 24 was 12, converted back because they had the bulbs, or some mechanic decided what's "best", or any combination of flawed logic. You wouldn't believe what goes on inside some heads that are supposed to know what they are doing, and get paid for it!

And that the wiring is how old, and been "repaired" how many times?

You might be well advised to re-wire the whole thing properly, and don't bother trying to figure it out.

You need the headlight relay so you aren't running the big power through the switch and dash wiring. A relay lets you run small wire and a small switch up at the dash, and then the heavier wire from the relay to the lights. Think about the amps when running 4 good high beams.

happy coaching!
buswarrior
BrianMCI96A3 (69.34.171.129)

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Posted on Saturday, October 09, 2004 - 12:51 pm:   

Okay, I'll tackle this...

Firstly, the relay is an important part of the system, while you COULD re-wire the system without it, unless you changed the headlight switch for a much heavier one, it would fail eventually.

The relay is there to handle the current load going to the headlights, so the headlight relay needs be working to keep that load away from the rest of the system.

The good news: So long as your relay is in good condition, it actually can make the job of changing to 12v easier.

There will be at least 4 wires going to your relay, two of them will energize the coil and at least two will carry current through the relay to power the lights.

If there are only 4 wires then you only need to determine which wire coming in to the relay is
24V + with the switch off.

At that point you can replace the 24V + wire to the relay with a wire carrying 12V + In this way the relay will operate as before, with 24V input from the switch, but will pass 12V through it's contactors.

This is the easy way... however, depending on how robust your system is, the higher current demands of 12V may cause a few issues to crop up.

I would test the system for several hours with the high beams on, using a battery charger to keep the batteries fed during the test.

With the high beams on, I would test every component by touch to see how well it is handling the load passing through it.

If any component other than the lights (switches, relay, wires)is getting more than warm to the touch and becoming hot or is already hot, you'll need to beef up that component (wires, switches, relay) or it will fail sooner than later.

Hope that helps

Brian
BrianMCI96A3 (69.34.171.129)

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Posted on Saturday, October 09, 2004 - 12:56 pm:   

OH...almost forgot, my suggestion would be to find the original headlight wiring schematic and return the wiring to that configuration, THEN replace the 24+ positive to the relay with 12V+

Brian
ChuckMC9 (Chucks) (64.105.16.131)

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Posted on Saturday, October 09, 2004 - 2:11 pm:   

For a very high-level overview of MCI's approach on the MC9 12v headlight setup:
Headlight Wiring - 12-Volt Lights on a 24-Volt System
Rob Talbot (12.202.162.5)

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Posted on Saturday, October 09, 2004 - 6:46 pm:   

Great help you guys are exceptionally nice to help me out with this. As far as the old system . . . I didn't check the voltage, but the old beams are 24V as marked. I have three questions:

Now as I look at my wiring and the diagram from MCI from the link above - page 3:

1) I am perplexed concerning the long tube which carries a #35 wire on one side a #34 wire on the other side. On the tube it says

Long Omite Tube
270 - 100M-40
2 Ohms =/- 5%
X-47

What is this for??? It might be for something separate from the lights, but the wire numbers are the same as the ones we are using for the lights. As a matter of fact the #34 wires are for the low beams and the #35 wires are for the high beams. These hook on the opposite poles of the stud blocks where the headlights for each side hook together.

If it is something I need how do I test it to be sure it works?

2) I had a #52 wire that was hooked up with the power wire #33 going into the dimmer. If the #52 wire was not on there with the power #33 going into the dimmer I could not even get the high beams to light. Anyone make sense of this?

I am wondering if the relay is bad? I might hook everything up according to the wiring diagram and then use the heater relay for the lights to see if that makes a difference. that wierd #52 wire is not mentioned anywhere on this diagram and I cannot figure out why it is needed to operate the lights.

3) I have a relay with four terminals on each side, but Brian is correct that two come in and two come out. However, there is also a #33L power from the headlight switch.

It appears to me that power comes into the relay at the "1 connection" through the #33L wire from the headlight switch. The relay also gets power from the dimmer at the "7 relay connection" through the #35P wire that comes from the dimmer and it gets low beams from the other terminal off the dimmer to "8 relay connection" and wire #34P (Odd since this was not hooked up when I took it apart).

From the other side of the relay goes the #34 (left and right) low beam wires and #35 (left and right)high beam wires

Long way to asking: Should I would hook up 12V power to the relay at #1 connector with the wire already coming from the headlight switch???

Then hook everything else back up like it was and see if it works without getting too hot.

Thanks again for your help wading through my situation and questions.
Rob Talbot (12.202.162.5)

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Posted on Saturday, October 09, 2004 - 7:05 pm:   

I just figured something out . . . the schematic I have been looking at is the 12v one for switching to 12V from 24V.

It is not the original schematic, so I don't know if all that stuff I just mentioned is relevant.
Jim Ashworth (Jimnh) (172.147.187.52)

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Posted on Saturday, October 09, 2004 - 7:59 pm:   

The tube with "ohm" on it is a resistor used originally with the 12v headlights on the 24v system to drop the voltage. You have a lot of work ahead since someone down the line has modified the wiring. This is the most difficult situation to troubleshoot and correct. I no longer have my MCI schematics, but perhaps someone else has that can copy and get them to you. At least they didn't cut and remove all the wires so you at least have a half a chance of restoring it. Good luck--

Jim
BrianMCI96A3 (69.34.171.129)

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Posted on Sunday, October 10, 2004 - 2:38 pm:   

Alright... the relay... do the contactors make connection through it to the wires for the headlights?

I think what I might do is take a jumper wire and attach it to the load wire coming into the relay

This wire should be hot all the time with the master switch on.

(As I mentioned before two wires coming into the relay will be to energize the relay coil, one will be hot when the headlight switch is turned on, and one will be a ground wire...)

I would then carefully touch the hot jumper wire to the #34 then the #35 wires leading to the headlights, if you get a violent reaction when you touch the jumper to either one you have a short somewhere, if no adverse reaction, attach the jumper to those wires in turn and see if you have lights.

If you do have all the lights lit, and you feel that the dimmer switch is in good working order then most likely the problem is in the relay...

I would use a test light to see if the output terminals on the relay are hot with the relay energized

If there is no juice at the output terminals but the relay clicks when power is going to the coil, then coil is still working, however the contactors might be fouled...

I have, in the past, been known to CAREFULLY remove the cover from a relay, and carefully, use a fine grit emery paper to clean the surface of each contactor...

Hope that helps... but with wiring it can be difficult at times unless you are can eyeball the situation.

Brian
Rob Talbot (12.202.162.5)

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Posted on Tuesday, October 12, 2004 - 11:03 pm:   

Brian this is great help. I am going to try this and then if all fails I'll drop back and punt. I found some 24 volt headlights -- finally. So if it gets too tough I'll go back to 24 till I have time to figure all this out. 24V headlights are 19.99 each at Napa - ouch!

Rob

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