Resistor bypassed or not, the front battery always handles the 12 volt loads...at least that was my understanding of how it works.
Not exactly. Well, actually, no.
To get clear on this, remember to look at the whole
system, not just the voltage going to the GPs.
In the stock configuration, 24v (from BOTH batteries) is provided to the GP
system. The resistor knocks that down and feeds 12v to the glow plugs. Where does that other 12v go? It's wasted as heat from the resistor. So the stock GP
system is a 24v
system. It draws its power from
both batteries.
The bypass changes all of that. The resistor is no longer doing anything except collecting dust. No power flows through it. It's just
there. Decoration. It's as much a part of the electrical load as a mud wasp nest on your firewall.
Instead, we draw 12v from the 12v system (front battery) and feed it to the glow plugs.
So, we have changed the GP system from a 24v
system to a 12v
system.
Clear as mud?
Now get that wasp nest off your firewall, willya?