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cranetruck · 12-28-2008, 09:14

Quote:

Originally Posted by steelsoldiers

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We hooked up some old batteries and ran a slave cable from Winslow's 5.9L Cummins powered M35. Once we had 24v to the cab I flipped the battery switch and NOTHING!! Doh!! Must be a bad protective control box. The sealant had failed around the edge of the box and the whole inside was corroded. The circuit board was fried in a few spots as well. Arghhhh!! Good thing we saved one from the 925 parts truck. We got that swapped in, flipped the switch, and we had power to the dash cluster! Yes!!!

Then, we decided to get the fuel-burning heater fired up......!

Good progress Chris!

About the control box, trying to "seal" it is a mistake, it has a rubber gasket for the connector and can never be sealed. You need to vent your new one, should be an 1/8 NPT plug on the bottom side somewhere. Open it and leave it open.

If you try to seal a printed circuit board, which generates some heat, within a box, there will be powerful forces at work, the difference in air pressure will pump molecules of water into the box past any rubber gasket or silicone, which will later condense and be trapped within. The only seal that works is a hermetic seal, preferable with an inert gas inside.
I have made thousands of electronic units enclosed in gasketed boxes (my old company for the trucking industry and ocean racing sailboats) and always vented them. Experiments showed that if I didn't, there may be as much as an inch of water sloshing inside within a couple of weeks.

To top it off, the control box I opened here, had lots of non-mil spec parts, so water will kill it fast.
Vent the box!