pre fuses on rt pass side in 76 280c
 

testing these 16 amp fuses in the three boxes mounted on firewall pass side theres 2fuses in one box power on both sides the other two boxes doesn't receive power on both sides fuses are new is there a short to ground or short to power ? asking for advice not sure if safe to jump ground fr the other box

Aren't those for electric windows? Even with the fuse installed you won't see anything happen unless you hit the window switch or jump those terminals at that point.

I'm not sure what you're trying to sort out.

testing power in power out yes wiring diagram says windows , aux fan. and ac clutch trying to troubleshoot why ac blowers don't come on just the defrost speed fan does testing power in power out fr fuse to changeover switch

Those fuses have nothing to do with the cabin fans. The A/C fuse is for the compressor and the Aux fan also has to do with the A/C by "by-passing" the auxiliary cooling fan's temperature trigger.

Not all A/C system installations used the fuse for the auxiliary fan. Some triggered it by using the A/C clutch circuit to activate the circuit.

thank you mike and thank you Mercedes doc