on page 32
The 70457501 section in hashed lines, near the 70457502 inscription you have the Y and Z named wires, you have the r102 10 ohms resistor, the resistor is between sw1 A2 pin and sw1 A4 pins.
In section 4 of the manual you have some theory of operations ,,,, reading it would give you some hints.
... switching an unregulated supply or the regulated +5v for the battery pack if installed ?? i think for the charging mode when the meter is powered off, the trickle charge or the supply charge, section 4,3,2
As i see it in the same page (p32), you have two similar sections /revisions made with different parts, an 3 pins regulator lm340, and the other made with transistors and a op amplifier
Your first post picture is the dc/dc 70457704 pc board, i would not connect anything on tp3, tp2 is the positive side of the battery pack.
I finally think the red wire may have been added to do something or bypass some part of the dc/dc board and go straight to the battery ?, since you wrote the board wasn't there when you got the meter, and the battery holder casing was there, the only logical place it would go is tp2, it may had another kind of battery installed ??
I don't like this wire at all, you should be very careful, i would remove it, there only the Z wire going to the front panel, all the other pcb traces are between the sw1 switch.
The 7045702 board is the front display, the Y and Z wires goes to an D44 led page 25 diagram 2.4
The B1 thru B10 are the dc/dc converter outputs / connection when inserted, i may have made a bad deduction, on the previous post