Popping fuse when AC/Fans are turned on

[jallen]

I need your help. I have a 1980 C10 Cheyenne. It has a SBC 350. I put two electric fans on it from Derale. I had an Old Air A/C installed last year around the same time. I ran that setup for about a year with no issues. The other day I popped the 20 amp fuse on my fuse box. It’s the one that controls the gauges. I have checked all the relay wiring, change it, changed the relays as well. I still keep popping that fuse.

I have checked under the dash for frayed wires. I checked the wires going thru the firewall. All other fuses are good. The AC fuses are good. No wiring is grounding out that I can see. I have cleaned up my grounds for the fans as well. I can unhook the fans and drive the truck and not pop the fuse. The moment I plug those relays back in and turn on the AC, the fuse pops.
What could be causing this issue?

 

[SirRobyn0]

@jallen Unplug the fan, unplug the high speed relay on the firewall, unplug the resistor. Put a good fuse in it. Does it pop then?

If yes, look over the wiring again and consider a bad fan switch.
If no start plugging components in one at a time, when you plug something in and the fuse pops you have found the problem.

Hopefully that will help you track it down.

 

[fast 99]

Could be just circuit overload. How many amps do the fans draw on startup? That in combination with other items on same fuse be overloading it. May have to run a standalone fused switched power supply from battery.