No start- Bad control box?

[cranetruck]

Appreciate the pictures, I'll get back to you.

 

[TedG]

Paul,

As mentioned on the phone, disconnect the wires on the side of the contactors and then measure resistance. This will allow you to measure actual resistance (if any) of the contacts, both energized and non-energized.

The silver relay in the 800 series box is: Stancor 70-903 and can be purchased for around $20 at Allied Electronics. Newwark might have them also. Iwould think that it could be used for this application.

If you need a backup control box to find a trailer (hehehe), you can borrow one from my trucks.

 

[steelsoldiers]

Here is an interesting article on the PCB and wiring on the 939 series: https://www.absmodtrack.com/m939/uploads/M939 5 TON FMTV VOLTAGE SPIKE PROTECTION.htm

 

[cranetruck]

Closed contacts (relay energized) should give you a reading of 1/2 Ohm or less for a new relay.

To help "burn off" some of the oxide on the contacts of the reverse polarity protection relay, turn on headlights and other electrical loads before flipping the master switch.

Note: When removing wires from the terminals, hold the inner nut with a wrench to prevent damage to the internal relay/solenoid wiring.

 

[steelsoldiers]

Here's a link to a previous thread on the subject: http://www.steelsoldiers.com/5-ton-up/11557-trouble-shooting-protective-control-box-5-ton.html with pics from Bjorn's box dissection.

 

[Armada]

Thanks for the links.
Update: I disconnected the wiring from the relays and tested all of the posts again for resistance. I get '0.L' reading on all positions, left to right, to center, etc.. So that means the relays are good, right? Let me know.
Thanks for the help.

 

[cranetruck]

Here is a typical schematic of a "normally open" relay/contactor. The coil may have a resistance of 100 ohms or so, the contact resistance must be measured when the relay is energized...

Edit: Based on the link posted by Chris, there may be some issues with the electronics since the designers apparently didn't consider voltage spikes that may occur when the engine is started/shut down and not to mention bad battery connections coupled with a charging alternator (load dumps).

 

[TedG]

Hi Paul,

Trouble shooting electricals via typing is dangerous. To measure resistance on a contactor, it needs to deactivated (as you did) and no ohms/open circuit is verified. If ohms were found, then you would have a stuck/arced contact, like points on older M-series gassers. The contactor will then need to be activated. Measure what the ohms are. If you measure ohms greater than 2 while the contact is activated, then you have buildup on your contact points.

I recommend that you put box in your car, drive to my house, and we will both test it! Safer that way...

 

[Armada]

I recommend that you put box in your car, drive to my house, and we will both test it! Safer that way...

Sounds like a plan, Ted. Plus I also need to do a little parts shopping at 'Teds MV Parts Emporium'.

 

[Armada]

Thought I'd post the final outcome of the intermittant electricl failure I was having. Maybe this will help someone else.
Turned out it wasn't the control box causing the issue.
After not finding anything wrong with the control box, I started a serious recheck of all grounding points. I removed the base from the firewall that the black box mounts too and cleaned all the mounting surfaces. I also used di-electric grease on the contact areas to help prevent corrosion. For additional grounding I added a ground strap from the box to the firewall too. Still had a problem.
Then I started looking at the main harness on the firewall and viola! I'll let the pictures tell the rest of the story.
The wire has been fixed, and the harness repositioned to eliminate the pinch point. I had went through the entire truck previously and insulated, zip-tied, etc., any wire/hose/cable that lay loose, vibrated, or sat against something it shouldn't have, just for this reason. I had overlooked this part of the harness.
The truck works like a dream again, just like it used to.

 

[bambambam22]

If a person was to need this done and does not have the back ground to know what you are talking about would you be willing to do it for me for a fee and if so how much? I have a starting problem with my M813 and have not found it yet and purchasing new batteries is next then I dont know wehre to do if that does not fix it but the batteries were installed in March of 2007 and I dont thnk they are bad and if they are not I have other trucks that I need batteries in anyway so I have to buy new batteries anyway but if new batteries dont fix my problem is it better to ask you to check and fix ( For a fee ) my controle box or buy a new one? Thanks Rick

 

[dm22630]

You can check the control box yourself.....it is very easy to do. All you need to do is turn the accessory power "ON" & if you hear buzzing.....it works. If there is no buzzing, it does not work.

 

[cranetruck]

Chris (steelsoldiers) will be testing a "bare bones" version of the control box over the weekend. It was put together by yours truly and the printed circuit board has been eliminated, which simply means that the "protective" features based on the "engine running" input (wire #566) are no longer present. The reverse polarity protection is still there, but it's up to the operator to follow the starting and shut-down procedures per TM to prevent possible damage with this box.
If Chris is satisfied and others want this "box", I would need the old connector (=old box) plus $200 to cover the cost of new 100 amp relays, labor and hardware. If you want to supply the relays along with the old control box, the cost would be $75.

 

[vinny-socom1]

good info.. Bjorn do you have wiring diagram for your new set up for dyi



Vinny

 

[cranetruck]

Sure, just have to dig it up...

 

[vinny-socom1]

Thanks I just has one fail and was thinking of rebuilding it so I have a spare.

Vinny

 

[cranetruck]

Circuit diagram attached...

 

[vinny-socom1]

Thanks!!


Vinny

 

[derby]

So if I have to flip the master switch back and forth a couple times to get power and then loose it when I hit the start button it is most likley the Relay box. Rebuild or replace?

Cranetruck, how have the rebuilt relay's been holding up?

 

[cranetruck]

So if I have to flip the master switch back and forth a couple times to get power and then loose it when I hit the start button it is most likley the Relay box. Rebuild or replace?

Cranetruck, how have the rebuilt relay's been holding up?

No complaints AFAIK, Chris (steelsoldiers) is the person to ask, he installed it on his M925.