Blower motor relay
 

I am pulling my hair out trying to figure out my blower relay on my 79. The low speeds do not work on my original. Bought a new. Low speeds work but high blows a fuse. I have bought three different and they all do the same.
The original will click when you ground pin 4. And add power to 3. But no continuity between 1 and 5. New switch continuity between 1 and 5. But as soon as you add power to 3 it sparks. A dead short. 3 relays all the same thing. See pics. What am i missing? Am i wired correct?

Re: Blower motor relay
 

Have you looked at the resistor?

Re: Blower motor relay
 

The relay in the pic is equipped with a suppressor diode. The arrow and line thing between 3 & 4. It is polarity sensitive. A short when +/- connected one way to 3-4, but open when connected the opposite.

By the little diagram on the relay side, 1-5 is closed when no power to 3-4 and 1-2 will be closed when 3-4 powered, while 1-5 will be open.

Don't know if the original relays came with suppressor diodes. But when computers became a thing in vehicles, suppressing voltage spikes when a relay coil is de-powered became important.

Re: Blower motor relay
 

I pulled the old relay apart and cleaned the points, it looks like I may be back in business