How to bypass PCB? I am aware some HMMWV owners have done it. TOBASH

[TOBASH]

Been replicating kboy's/ TOBASH's diagrams. Thanks a million for posting all this info up!

Background: My smart start box was sitting on the floorboard and the harness was chopped instead of being disconnected when I picked it up from Yermo I brought all all the chopped wires ends into a small Harbor Freight water tight box. All the splices are under the sheet of aluminum and the relays are mounted via nutserts. I mounted the box on top of the footwell for ease of wiring and future serviceability:
View attachment 943950
(Ignore the 60 amp circuit breakers, leftovers from another project, just used for mockup)

Its always bothered me that there are no fuses/breakers. I am adding 3 to the system to ease my mind with the higher amp items. Currently I am connecting the following from the engine side of the harness running to breakers:

• Terminal D (wire 575A, 24v to glow plugs)
• Terminal F (wire 5B, 24v Run HD engine electrical)
• Terminal E (wire 81A , 24v source always hot)

(The relays are 24v, 200A)
If one were to add circuit breakers, what amperage would be appropriate?

Just be aware that using a plastic box is potentially an issue because it is flammable and it is dealing with high voltage and high amperage. Just one wrong wire can cause that all to catch fire.

I recognize that car companies are using plastic boxes however they have extensive teams to make sure that they have not created cross circuits.

Each one of the hobby builders is creating a one-off item, so mistakes can be made.

 

[wjeeper]

Good point. I have tested all the circuts and they are working as planned. (once I take care of the missing injector return line, and add diesel it should be a runner again)

I am not at all concerned about using plastic housing. A metal housing being conductive every where seems like a bigger chance of a bad connection causing a catastrophic failure. I have done 5 or 7 manual glow plug control boxes like this on Kubota/ New Holland equipment when the spendy glow plug controllers kept going out (lots of cold starts in N. Utah). Had to train the employees to not "over cook" the glow plugs when starting them. I would bet those control boxes have a combined 2000+ hours on them with no problems *Knocks on nearby wood*

Since my relays are 200a each, the total of the breakers should be less than 400a so that it trips the breakers before it fries the relays? But the glow plugs and start relay shouldn't be active at the same time, so as long as the glow plug breaker is under 200a, and the others that are on when the engine are under 400a

175a? Terminal D (wire 575A, 24v to glow plugs) a C3500HD with a 6.5 uses a fusable link that appears to be 12-14 gauge
185a?Terminal E (wire 81A , 24v source always hot)
200a? Terminal F (wire 5B, 24v Run HD engine electrical)

They aren't cheap, but I feel they are necessary to prevent a total failure/ electrical fire

 

[Ajax MD]

PCB- Prestolite Edition:

At least for the Prestolite box, Kboy is right. If you want the "Wait" light to function, it needs to be connected to the (-) or ground side of the secondary relay.

-The Prestolite box has three relay-looking devices in it. You can safely reuse the steel-bodied, Cole-Hersee looking relay.
-The other two black, plastic bodied relays are not the proper pole/throw configuration to use as the secondary relay.
-The Cole-Hersee relay being metal, is grounded to the box which is grounded to the body of the truck, thus only one small terminal (+24v) is needed to activate it.

Although I'm electrically/electronically inclined, I still had some "duh" moments while interpreting TOB's diagrams. That's my fault, not his.
"Before" pic attached for reference:

 

[Ajax MD]

For the secondary relay, I purchased the same kind that some other guys in this thread have used.
I took special care to find ones that were rated for "continuous duty" even though the secondary relay is only momentarily engaged for the glow plugs because Amazon is sketch sometimes. I wanted this relay because I thought it might be more compact. It is, but not enough to matter. Two Cole-Hersee relays would fit fine.

https://tinyurl.com/2ed8kv4b