If you measure the resistance across the loudspeaker posts which include connection to the bass driver (or full range) then you will measure some resistance that is greater than 0Ω which is made up of the crossover components and the voice coil resistance of the bass driver only. You are not measuring the impedance of the loudspeaker, in fact an impedance measurement doesn't mean anything unless you know the frequency you are measuring at.
In your configuration you should see open circuit for MF/HF and some resistance across LF. Which you do when the crossover is disconnected from the speaker terminals.
If I understand you correctly it is only when you put the loudspeaker back together that you read 0Ω across the MF/HF. If that is correct then you have a short which is upstream of the crossover i.e. the loudspeaker terminals, connecting wires etc.
If the MF/HF connectors really are a dead short then your amplifier would fail immediately... actually it should go into overcurrent protection but I digress.
Something doesn't add up.
1) You measure 0Ω across the MF/HF terminals of both speakers.
2) When you had everything disconnected you measured open circuit across IP+ & IP-. That is what you would expect.
Knowing that, it should be simple with the crossover disconnected to measure the resistance across the loudspeaker terminals to locate the short. If there's not one then the short was either at the point the wires connected to the crossover or items 1 & 2 listed above are incorrect.
The fact that both speakers measure 0Ω at the MF/HF terminals implies that you're not looking for a stray wire or small solder bridge but a mistake or failure on both speaker inputs. That's why something like connecting the amplifier outputs incorrectly seemed like a likely scenario... although I know you've ruled that out.
In your configuration you should see open circuit for MF/HF and some resistance across LF. Which you do when the crossover is disconnected from the speaker terminals.
If I understand you correctly it is only when you put the loudspeaker back together that you read 0Ω across the MF/HF. If that is correct then you have a short which is upstream of the crossover i.e. the loudspeaker terminals, connecting wires etc.
If the MF/HF connectors really are a dead short then your amplifier would fail immediately... actually it should go into overcurrent protection but I digress.
Something doesn't add up.
1) You measure 0Ω across the MF/HF terminals of both speakers.
2) When you had everything disconnected you measured open circuit across IP+ & IP-. That is what you would expect.
Knowing that, it should be simple with the crossover disconnected to measure the resistance across the loudspeaker terminals to locate the short. If there's not one then the short was either at the point the wires connected to the crossover or items 1 & 2 listed above are incorrect.
The fact that both speakers measure 0Ω at the MF/HF terminals implies that you're not looking for a stray wire or small solder bridge but a mistake or failure on both speaker inputs. That's why something like connecting the amplifier outputs incorrectly seemed like a likely scenario... although I know you've ruled that out.