Ray,
I have a pair of PRR F7s from the first run. I also have a pair of E7s and FP7s. They do not overload my system.
I have an 8 Amp Digitrax system also. I do have 2 additional boosters and the layout is divided into 3 districts. But the F7s and 2-3 other locos can run in any of the districts, without overload. I am wondering if there is something else going to overload your system. Perhaps you have a bunch of lights or light passenger cars, or maybe stall motor switch machines powered off the track buss?
I am not sure which manual you have. I have one that is 434 pages, and one that is 376. Each seems a little different. However, the headlights and backlights are on the same CVs. so look up in the table of contents "Headlight" and then Headlight initial state and then the same for the "Reverse Light". Just focus on those few pages and learn about them. I documented the changes I made on my E7s and could send you that. It is written more in english than the manual.
By the way, since you have digitrax, do you also have any PM42 or PM4 breaker boards in between the command station and the track? The breakers on them may be popping. They default at 3 amps if you did not change them.
