[Rules] Leader effect on APC's morale

[Poor Yorek]

I kinda think Rules as Written is appropriate here.

That is the point: the rules-as-written imply the general principle that the ability to activate conveys full use of the leader's capabilities unless explicitly prohibited (I agree with Peter here).  Regular leaders can activate towed artillery and SPA's both of which have BF values. Thus, a leader with a combat bonus can combine their fire subject to the regular restrictions and provide his morale bonus to both unit types in the absence of a RaW prohibiting it. Please note that I am NOT saying that one can do "anything" not explicitly prohibited by a rule, but in this case, the general principle is already established and thus should apply in the absence of an exclusionary provision.

though I think there is little precedent of SPA and towed artillery working that closely.

Presumably the paucity of scenarios with the two types on-board reflects this.

Some possibilities from the German side might be:
SPW-250/1 or SPW-251/2 (?) with, say, regular 81mm.
120mm with a Wespe (or even Wespe with an 81mm albeit the Wespe would need to be "forward").  

Of course, whilst this might be a way in some scenarios of boosting BF, one does pay the price of dedicating a combat modifier leader to the purpose rather than for DF/Assault actions.  So whether the choice to do so is wise or not ... :hrug::

[zaarin7]

Historically the US Army used Fire Direction Centers at divisional level to coordinate fires. And a lowley platoon Lt. could, in the right circumstances, call in a Corps worth of support. PG dosen't go to that level and really shouldn't except in games like Cassino.

[joe_oppenheimer]

but since they can already fire as a group if up to 3 arty units are located together, same hex or adjacent (my understanding), they don't need the leader to coordinate the fire.
Tom Oxley

That's not correct. On-board artillery in different hexes can only combine fire with a leader:

Units in different hexes may not combine Bombarding units stacked in the same hex may combine
their fire values without assistance from a leader. Bombarding
units in adjacent hexes may combine their fire values
only if a good order leader with a combat modifier is in one
of those hexes (6.41, 7.33).
(from the fourth edition but rule is the same in the third).

You may be confused by the rule on off-board artillery:

Up to three off-board artillery increments may combine into one fire value, but may not combine with on-board units.

[thomaso827]

I may have confused it then. I believe I did play it right even if mis-remembering it now that I think about it. It comes up in a few Pacific scenarios where I didnt want them to be a bigger target by stacking all three in one hex. I'll blame it on that "age appropriate memory loss" thing I was told I might have.

Tom Oxley