There's SO much I could say, but so little time.
First, you're confirming what a lot of us have suspected: the factory system (when working) is far better than a pushbutton system.
Sometimes, it's the simplest of problems. Since you're getting current at the bar, we can eliminate one of the more common problems: bad electrical connection at the fusible link going to the #1 glow relay.
That bar (or part of it) is a sensing resistor. As the plugs heat, their resistance increases (I believe). That signals your QOS controller (on the driver's kick panel in the cab) to cut them off. There is one wire connector between the engine and the firewall that this circuit goes through. I'd track that down, disconnect it, clean the terminals, plug it back up, and try again. Ditto for the other connections to the bar and to the block. On the other hand, there may be a bare wire that's shorting it out somewhere. Check for insulation that has rubbed away. I know of someone who had that problem. Since they're usually greasy, it's hard to spot.
Edit: I didn't read carefully enough. I just noticed this:
INeedLUV wrote:
Could the problem be that the original bar that connects the glow plugs is gone and they are now connected by wires and ring terminals? Would this cause the system not to function at all?
Most definitely. Someone at IsuzuPup.com should be able to help you with this part, and others that you're missing.
Hope that helps.
Jack
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'83 Isuzu P'up Diesel LS - Original Owner
JoeIsuzu@IsuzuPup.comIsuzuPup.com