I've got a chevy K5 blazer built in 79.

The blower doesn't work. If I attach the blower directly to the battery it works, but it doesn't work over the switch.
Perhaps the problem is the fuse or the relay.
The fuses are mounted under the steering wheel, but I can't find wich fuses are attached to the blower.

Does anyone has a shedule about how the blower is attached? And where is the relay mounted? Or is there another problem?
NB also the speedometer doesn't work. any ideas about that?
Thanks.

 

Have you tested for power at the blower motor resistor pack? Or what goes into the fan speed switch in the dash?

Does your truck have A/C? What speeds are there for the blower motor?

 

Check your switch with a test light as well and make sure its not having issues.

 

I've tested the switch. There's one common contact and three open contacts. The switch is working correctly.

But I can't find the motor resistor pack.
Where is the motor resistor pack mounted?
Thanks again.

 

It'll be located in the blower box that is attached to the firewall. It is right next to the blower motor and is held in with sheet metal screws. Should have 3 or 4 wires running to it.

This view is from my '74 which should be quite close to your '79 unless you have A/C in which it will look different.

 

Ok I've found the motor resistor pack thanks to your help.
It was located in the blower box.
There are four wires running to the relay. One red, one orange, one blue and one black. The red wire is the biggest. Do I need to have 12 volts between the red wire and the black wire? The black wire is the zero.

 

This is the best diagram (attached) that I could find that showed a relay... Not sure what year it is from, but the fact that you only have 4 wires to the relay probably invalidates this as being your setup. My references only go back to '82 and they all show 5 wires at the relay. My hard copy references are for a '74, but I don't have them with me at the moment.

 

Arrgghhh.. look at the heater only diag. Could they POSSIBLY make it more confusing?!!! No way that diagram is correct ... unless there's a magic resistor that boosts voltage.

Here's what I've found in sparse experience with both Ford and GM blowers. If you check at the resistors and find no 12v in any position, on any setting, yet the blower works, then the problem is most likely at the 12v input to the speed selector switch or upstream - toward battery- of that. And that applies whether there's a hi-speed bypass relay or not.

What I suspect MIGHT be happening is based on my experience with my son's 79 Buick Regal.. I had to fix several connections where the terminals did not penetrate the wiring insulation properly. sometimes there would be evidence of overheating at the wire-terminal junction, sometimes not.
On the chance your truck's harnesses were made by the same supplier, I would look for that.
Given it's the blower circuit I would look for overheated insulation.
Point being: there's power through the wire but the terminal doesnt get it.

Note: On a re-look at the 'ac only' diag, see the blower speed switch input comes from a 'selector' output, which implies there was more than one way to shut off power to the fan. IOW, you could select 'off' as well as AC/heat/def etc. so FIRST you're looking for 12 v {the brown wire or whatever} going into the heater control panel. If you have that, then your problem is highly likely to be in that 'function= off' switch

- Does your truck also have an underhood fuse panel?
- Usually you can test fuses with them in place.. you want to use a 12v test light, one probe to chassis.

If it lights on one side of fuse and not the other the fuse is blown. If it lights on neither, try with key in both acc and ign positions.

 

Yeah, I questioned the heater only side of things when I first saw it as well, but it was the best I could find without spending more time that I don't have searching. If you have the time, have at it.

 

Heck that wasnt a critique of you, you didnt draw it. and any diagram is better than none at all just for the visualization.

I have a feeling that diag might be pretty close, otherwise.

Made me think about that Buick and a 73 Olds I had... had both blower speed off and Heater off positions, IIRC.

So Beukert.. I think you're looking to find if 12v comes into the controls at all