Inside a 3 lever BO Switch...

[N1265]

Well I took apart one of my 3 lever switches today and I have a couple of questions.

In picks #4 and #5 :

1 ) What is it ?
2 ) what does it do ?
3 ) Do they ever go bad and need replaced ?


I figure that in picks # 6 and #7 this is the 20 AMP internal Circuit Breaker that everyone talks about.

Therefore in picks #6 and #7 :

1 ) Do they ever go bad ?
2 ) can you solder a heaver CB in it's place ?
3 ) can you just bypass it completely ?

 

[doghead]

The first 2 pictures are a resistor(30 ohm, 5 watts), it's used to reduce the voltage to the gauge panel lights(dim, bright).

I am not 100% sure from your picture, if the other two pictures are the thermal circuit breaker(but I would guess so).

Yes, either can go bad, the resistor is easy enough to test/measure. The CB, to "cycle" it, not so easy. yes, you could bypass it, but then you wont have any circuit protection(something will melt or burn or both if you have a short).

Did you have a problem, why did you take it apart, what's your goal?

 

[N1265]

The lighs in my M880 keep clicking out after a while , expecially when running trailer brakes, emergency flashers or high beams.

Over the last couple of years I have gone threw everything and a while back I replaced the BO switch and it cured my problem, but it has since returned.

I thought about making a " bypass plug" to plug into the female end of the plug and do away with the switch altogether, however I am having trouble figuring out how to jump the switch.

I know of a few other M880 owners who have the same problems but so far nobody has been able to find a pereminat solution to the problem except to do away with the BO system all together.

So instead of having to buy new switches I am looking to repair or modify one I already have.



The inside of the switch looks good, no burnt or coroded contacts and no evidence of poor quality in materials or craftsmanship, but you can hear and feel a definate " click " from the switch when the lights cut out.

It seems to me that the clicking noise has to be from something mechanical. witch would leave the CB or the actual switch contacts. Looking at the design, the contacts are spring loaded so I doubt they are the problem. I am thinking that the CB is the thing making the noise when it trips but I could be wrong. the only thing I can see that makes we wonder is that the contact area of the CB looks kinda small, but not much smaller than the switch contacts them selfs.


If I was to bypass the CB and then wire an inline fuse to the main power feed to the switch would that be good protection ?

How big a fuse could I run and still protect the lights wiring ?

 

[NDT]

The click is the bi-metallic thermal circuit breaker snapping open. Bypassing it as you say and installing a greater than 20 amp fuse sounds good.

 

[Boatcarpenter]

This link may help some.
http://www.steelsoldiers.com/electrical/7047-testing-cleaning-repairing-light-multiswitch.html
BC

 

[doghead]

You could use a 20-25 amp slowblow fuse. I think you might want to measure the total load on that circuit, to determine what the amp draw is, then confirm that's what the total lights should draw. then make a modification, if needed.

You could use a relay and supply the headlights, directly off the alternator or battery and relieve a large portion of the load off the switch.

 

[N1265]

A few observations :

1) I applied heat to the CB and confirmed ( like NDT noted ) that the noise is the CB snapping open.

2) The switch in the link provided by BOATCARPENTER seems to be a much older style than mine, I can not even see a CB in the one in the write up and mine has no snap ring .
I am wondering how they use to protect the wiring in the older designs, without a CB. I would suspect with a fuse or an external CB. Does anybody know for sure ?
However, this is still a good link because it will save me much time figuring out where the contacts go for the switch, ( This portion is switches are the same ) thanks for posting it.


I have no clue on how to measure the total load on the light circuit to determine the draw but the idea of running a headlight relay sounds good and I might have to resort to it .

Now I thinking I will bypass the CB and install a fuse or maybe even a higher rating external CB. Dodge put one on these ( 15 amp Circuit Breaker ) in trucks for the running lights and they are easy and cheep to come by.

If you guys have any other thoughts or suggestions please keep on posting them, I won't be able to do anything for a while yet.

 

[steelandcanvas]

The click is the bi-metallic thermal circuit breaker snapping open. Bypassing it as you say and installing a greater than 20 amp fuse sounds good.

Not a very good idea to install a fuse larger than the wire can handle. The CB is tripping out for one of two reasons. It is fatigued, or you are drawing more current than was designed for the system. The CB could be indicating something is wrong. As earlier suggested, you do need to find out what the current draw is when the CB trips. Do you have a DC Ampmeter?

 

[kc5mzd]

Have you thought of getting LED lights? They have LED replacement light bulbs out now that you just install in place of your old light bulb. I think if it is acting up because of a old worn out breaker then the lighter load of the LEDs should make your switch last for several more years maybe even the life of the truck...

 

[N1265]

I do not have a DC Ampmeter. I could probable borrow one but then I don't know how to use it.

According to the The wiring diagram I have for this vehicle, the lights on this vehicle are 16 and 18 ga. any idea how many amps a 18 ga. wire will handle ?

One thing that puzzles me is that everything works fine until you hit the 45min to 1 hr mark, Then click and lights out... would the system draw more based on the amount of time used ?

 

[N1265]

I did just spent $20 bucks for 4 LED 1157s and dash lights, However the dash lights were way to dim, and the 1157s bulbs I got would either work as running lights or flash for turn signals but not both, This confuses me because all 4 1157s have two filiments.

 

[319]

Not being familiar with the M880 series, but it seems as though the three lever switch cannot handle the total load of the lighting system, especially when adding the load of trailer lamps, hazards and high beams. Do you happen to have halogen headlamps? They would increase the load also. Might be a good idea to modify the system with relays to handle the load instead of the switch.

 

[G-Force]

I do not have a DC Ampmeter. I could probable borrow one but then I don't know how to use it.

According to the The wiring diagram I have for this vehicle, the lights on this vehicle are 16 and 18 ga. any idea how many amps a 18 ga. wire will handle ?

One thing that puzzles me is that everything works fine until you hit the 45min to 1 hr mark, Then click and lights out... would the system draw more based on the amount of time used ?

Just from that comment it sounds like you have a bad connection/ground someplace. I would hook up an amp meter in series with the circuit breaker and monitor the amperage. See if it goes up when the tghermal breaker trips.

 

[N1265]

Could it be a bad Neg. cable at the battery ?

 

[Ferroequinologist]

N1265, I had the same issue with my switch in my first deuce. I know you said you don't want to buy another one, but I've seen them go for $40 on Ebay, and you already spent $20 on LED lights your not happy with.

My deuce would do the same thing, especially if I ran the convoy lights (they are designed to draw off the headlight circuit) or had a trailer. Just a few extra amps would trip it, even though I know it wouldn't get near 20amp total. (had a clamp on amp meter) And I could drive it for various periods of time before it would start doing it. Sounds very much like a fatigued CB.

Once I replaced the switch, I never had another issue, 4ways on, convoy lights on, highbeams on. Still only drew 18.2amps.

If you buy a switch and it isn't the issue, you can always resell the switch to another member or keep it as a spare for when your 'original' switch fails (and it will eventually, usually at night, in the rain)

 

[Stretch44875]

I have had a couple 3 lever switches with weak CB's. They would trip when trailer lights were connected, or hazard lights used for a longer time.

 

[cranetruck]

My solution was to add relays as shown in the images below (posted several times in the past too, for that matter). This gives me 100% control of the light circuits outside of the 3-lever switch and its 15 amp CB, but still letting it control the basic operation as designed.
The relays selected are 25 amp mil spec units and they leave only a small current for the 3-lever switch/flasher module to handle.
Losing my lights one time was all it took, some years ago...

 

[319]

This is on his M880 which is all 12V if I'm not mistaken, and correct me if I'm wrong, would increase the load to the switch because of the lower voltage verses a 24V system. Seems as though it's possibly a design flaw.

 

[N1265]

A bad or under AMP CB is what I am leaning toward right now, everything on the truck has been checked and double checked. and the fact remains that the problem was cured by replacing the switch with a Brand New one ( but unfortantly the cure only lasted about 10 months ) I am therefore awful hesitant in thinking that another NEW switch will provide lasting results, Especially when you consider that the M880 BO system was not designed from the original consept of the truck, It is a military 24v set up that is spliced into a civilian 12V system in an attempt to make them field operational, Not being an electrical engineer I admit I am a little out of my comfort zone on this, This is a learning experience for me ...

So let me make sure that I am on the same page here with a few suggestions / comments that have been posted :

1) This is a thermal CB, Therefore heat of any source will trip it, so the problem may not be entirely due to the current flow. In theory, raising the temp of the switch ( weather it is a hot day, or heat from the blower motor ) may contribuite to the CB kicking out .

Is this a true statement ?


2) I have always been under the impression that the CB in these switches were 20 AMPS, I get this information from reading various posts in other threads witch may or may not be accurate. However after reading an above post, I am to believe that these CBs are actually 15 AMPS. Does anybody know for sure what the CB rating on these switches actually are ?


3) It was suggested that I may be dealing with a bad contact, I'll buy that. So Having the switch apart lets start there. In the photos below ( and I know it is hard to judge these things by a picture ) would it appear that the contacts in the switch itself are dirty enough to be part of the problem ?

Many thanks for your guys help.

 

[kc5mzd]

I did just spent $20 bucks for 4 LED 1157s and dash lights, However the dash lights were way to dim, and the 1157s bulbs I got would either work as running lights or flash for turn signals but not both, This confuses me because all 4 1157s have two filiments.

I am not sure what kind of LEDs you got but some have the LED on the top and others have the LED part on the sides. Try to get the dash light LEDs that have the LEDs that point in the right direction they will work a lot better.
You may have a 1156 in a 1157 socket somewhere on the truck. This could cause your electricial system to overload.
The wrong lightbulbs can cause higher than normal currents. I have seen major electricial problems with a car's entire electricial system fixed by puting the correct 2 pin bilnker taillight bulb in where someone had put a 1 pin bulb into a 2 pin socket. It can make hard to find ground loops in other systems.