Steve:
Regarding Jay3000's observation of both wires being hot at the blower motor, does this suggest the blower motor regulator is the problem (no ground)? Does the normal (one hot and one ground wire) apply when the blower motor is OK but turned off, or only when it is on and functioning correctly?
Also is there an easy way to trouble shoot the regulator short of replacing it?
I have an 85 300SD and had the blower motor replaced with a used one (I gambled and may have lost). It worked great for three months, then started working erratically and then low speed only, and now not at all.
I was hoping it was the fuse, but despite various suggestions as to where to look, I haven't found the "outboard" fuse. Does this model have one? I noticed it is listed on the fuse box list.
Thanks for any and all replies.

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1985 300SD CA (low miles 180k)
1977 300D (RIP)
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In theory, there is no difference between theory and practice. But in practice, there is.