Vehicle is 87 300SDL. As the title states Fuse 5 blows as soon as the ignition is switched on. Here's the nitty gritty detail on what I found when trying to sort this out.

I was told the SDL probably needed a new klima relay. Tried a used one and no go on the AC. Found the 50 step test procedure for the AC circuit and immediately found no power to pin 5 to the klima. Procedure says to replace the fuse. Find a good fuse in place but a blue fuse rather than the specified white fuse. (Not a good thing I figure) Move on to the X26 plug and find there is no power to pin 2. Trace a bit further and find the black/red wire supplying power is cut. (Uh Oh). Reconnect the wire and now have power to pin 2. Re-connect the X26 plug and the now proper fuse promptly blows when the ignition is turned on. Dig a little deeper and find the cable that includes the wire between the X26 pin 2 and pin 5 to the klima has been cut open and the wire itself probably tested. There is continuity between the two pins but obviously there is a major short or major current draw on the circuit somewhere.

Sorry for the excruciating detail but power/circuits is not my strength. The previous fix was to simply cut the power. Any specific/suggested steps to isolate the actual problem or what on the circuit may draw on a major basis? Thx.