blower motor wiring question

[incoma]

I've been having sporatic problems with my blower motor not working. With everything in the truck off, and the key in the "on" position, I can hear a light click when I turn on the blower fan, but I don't always turn on the blower. I'm thinking the heater resistor may be failing, but how can I be sure? I don't want to swap that and it turn out that the blower motor isn't working..!!

If the blower were bad, would it sometimes work and other times not work?

[70GMCer]

You need a volt meter to see if you are getting 12 volts to the motor when it is heater control switch is on. Test it at the firewall where you unplug the wire that is on the motor. Turn the fan switch on and then take 1 meter test lead to that wire and the other lead to a negative ground. If the meter shows 12 volt, it is good. Do this to all the speeds on the heater control. If no voltage, work your way back to the heater control testing for voltages.

[centsless]

Do exactly what 70gmcer said, then check the ground. With the fan on, touch the volt meter leads to the negative battery post and to the ground on the blower motor. By doing this you are checking voltage drop. It should be minimal. If it reads anything over about one half of a volt, you have a ground problem. You can do this on any circuit. The volt meter measures the difference between the two leads. The voltage at one end of the wire should be the same at the other, that is why the reading should be as close to zero as possible. Hope that helps !

[incoma]

ok guys, thanks for the help. I played with it yesterday - not using a meter, just disconnecting and reconnecting things and it started working. Not 100% yet, but 75% of the time. I'm going to find some electrical grease and see if that doesn't fix the 25% of the time. If it doesn't I'll hit the volt meter. I'm not the best with wiring troubleshooting and try to avoid it at all costs!

[jhow66]

The click you hear is the blower relay on the pass. side up by the right side of glove box. If you can move the relay it means that the ground wire is not making contact all the time.The wire (black) hooks to one of the screws that mount the relay to the heater and AC box.To check it just run you a jumper from the relay to a good ground. If it works all the time then you have found your problem. (the above advice carries no implied warrenty)