Please excuse me Steve while I post on this closed thread.
A few comments on the design. These are in addition to Steve's comments in post #12 which you should also read carefully.
The CPH3105 is specifically rated for a maximum base current of 600 mA, and this suggests to me that it's designed to monitor load currents directly, without a separate path for most of the load current. But...
C1 and C2, 22 µF capacitors from Q1 and Q2 bases to ground, and the smoothing capacitors in the switching LED drivers, will cause a large current spike in the base-emitter junction of Q1 and Q2 when power is applied. Depending on the rate of rise of the voltage on M1's drain, this spike could easily be enough to damage Q1 and Q2.
Characterising LOAD1 and LOAD2 as "175 mA" is a misleading oversimplification. They are actually switching converters, and their current draw will vary over a moderate range in roughly inverse proportion to their supply voltage, so they have a negative resistance characteristic, so they're neither a resistance nor a current sink. I understand that you can't easily model them in the simulator, but any or all of those factors could be important to us humans who are trying to understand the setup, and should at least be shown as comments on the schematic. Please bear this in mind for future times when you are about to redact potentially important information from your schematic and/or your description. We should not have had to wait until post 18 before discovering this important information.
As for the issue of continuous power dissipation in the transistors, I think it's worth investigating. You didn't mention this, but Q1 dissipates extra power due to the emitter-collector current that feeds LOAD2. This is a lot less than its base-emitter dissipation, because Vce(sat) is typically only 100 mV, but it still exists.
The CPH3105 data sheet gives a maximum Vbe of 1.2V at a base-emitter current of 100 mA and a collector current of 1A. Q1, and especially Q2, run at a much lower collector current, and collector current does affect the Ib vs. Vbe relationship, but not to a huge extent, and as far as I can tell using LTSpice with common transistor types, reducing Ic will also reduce Vbe for a given Ib, so you would be erring on the safe side. Assuming LTSpice's transistor models are accurate in this respect.
As for the actual maximum continuous load currents, they will occur with (a) minimum supply voltage, (b) maximum voltage drop across L1, D4 and M1, (c) maximum base-emitter drop in Q1 or Q2, (d) maximum Vce drop in Q1 (for LOAD2), (e) minimum efficiency in the LED driver (95% in the table in the data sheet, but this is not guaranteed), maximum LED current (6% high for an LDU08xxxxxx), (f) maximum LED forward voltage at that current, and (g) worst case temperature extremes for all of these. I don't know most of those figures; you should work them out. In the meantime I would design using load currents of 250 mA AT LEAST, preferably 300 mA.
Ignoring the small current through R2, and assuming that the 1.2V maximum Vbe at 100 mA also applies at 300 mA (NOT a valid assumption), the worst case Q1 dissipation would be (0.3 * 1.2) + (0.3 * 0.1) = 0.36 + 0.03 = 0.39W, say 400 mW. Based on any of the thermal resistance figures I've seen in this thread so far, that is a problem.
These calculations all relate to steady state conditions. The possibility of damage due to capacitor charging currents at switch-on is a separate matter and could still be an issue even if the steady state dissipation is within limits.
I would use a different approach. First, if possible I would avoid monitoring the load current in the first place! That's just because I don't know why it's necessary. If that's unavoidable, I would insert a proper diode (e.g. 1N4001) in each load path, and add a tiny amount of resistance somewhere (e.g. in series with D4, which is only rated for 1A continuous anyway), to minimise the turn-on current. Then monitor the drop across the diode with a transistor operating at low current. (You may need some small components to ensure enough bias voltage under all conditions.)
Other general comments:
That seems like an awful lot of circuitry. Apart from the overvoltage protection (D2, D3, Q3) and the pass MOSFET, what functionality is actually needed? Why is it necessary to turn the pass MOSFET OFF if either of the loads goes open circuit?
What is the purpose of D7, Q5 etc? Are these just to ensure that Q4 and the pass MOSFET remain ON for a short time at power-up? They will also have an effect if the input voltage is low; is this not a problem, or is it intended behaviour? If the latter, what is the reasoning behind it?
Is this an exact copy of the circuit in production? If you're about to answer YES, please think again. I doubt that a designer would use two zeners in series (D2, D3) when one is available in the right voltage; I assume this is a change you made because of LTSpice's limited component options. I have done exactly the same thing myself. What other changes have you made for this and other reasons? Is M1 really an Si7113DN in the production circuit? If not, please add an indication of the actual part number, the way you did for Q1 and Q2. Are there any other differences? Please look carefully.
In this application, are the fog lights and the reversing lights actually always driven at the same time? They have different purposes, don't they? Is there another part of the circuit that you haven't shown? If they're always driven together, why not use a single LED driver and connect all four LEDs in series? Is it because the fog lights and the reversing lights are too far apart? Or because there is not enough voltage available from the drivers for four LEDs in series?
eem2am, you can post any response to this once Steve reopens the thread, or PM them to me if you prefer.