Ground issue on the fan blower

[Greg5OH]

So i had no blower fan, i get voltage at the blower plug but there is nothing on the orange/black wire which should be ground when my wife cycled the switch. I added an aux ground to test it as you can see in the pic, just tapped that onto the battery negative terminal. The blower fired up, but the issue is that it is only high mode, i cant get it to cycle to lower speeds. The resistor in the air box is good. Again, I am dumb electrically..any idea where the issue may be?

If you follow that orange/black wire, in the engine bay it splits to the blower resistor, and then inside the cab it runs into the function selector switch (off, ac max, defrost etc). I have tried two sets of switches as well to rule it out (and i know mine worked before this massive rewire job, so obviously I messed something up)

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[LCAM-01XA]

Pop the heater controls block out of the dash again, unplug the blower speed switch, put the vent selector on anything but off to power up the blower, then start checking for voltage on each pin in the speed switch connector. You should see some voltage on all but one pin, if you're using a voltmeter instead of just a test light you'll probably notice different values for all voltages (courtesy of the resistor pack in the blower housing). Then measure resistance between the one pin with no voltage and any known good ground (should be one next to the fuse panel under the dash) - you should get close to zero ohms, basically a short circuit. If any of those fails that narrows down your search area. Notice how you're testing just the wiring, and not the speed switch itself - if you pass both tests the switch is your issue even if you think it's good.

Wire color codes coming tomorrow if you need them, the EVTM is MIA right now, I think I know where it is but the path to it is dark and scary and likely blocked by manbearpigs and possibly rabid werewolves.

 

[franklin2]

The orange/black is the ground wire. The brown/orange is the hot wire. The brown/orange feeds power to the blower motor anytime the keyswitch is on. Power flows to the blower motor on the brown/orange, and the flows out on the orange/black. It then splits and goes to the resistor and the selector switch. On high, the switch grounds the orange/black just like you did, and the blower runs full speed. Any other position on the switch the power from the orange/black has to run through the resistor and then back to the switch. Eventually inside the switch there is a black wire and it makes it to ground.

I would try to get it to work on high first. That's the simplest circuit, goes from the motor through the switch and to ground. If you get voltage on the orange/black, then you don't have a ground on that wire in high.

 

[typ4]

Check harnwess grounds and the one near the fuse panel also. As franklin says ,the speed switch controls negative , not positive.

 

[Greg5OH]

It were the grounds. Ther eis a large 3 prong round connector has two green type wires and a bloack wire, all large gauge. That ground wasnt hooked up. Hooked it up and all was well.
So i went to try to do the blower relay upgrade...no friggin dice.

Tried splitting the red/brown and the brown/orange wires individually and using either side as the trigger on the relay..but nothing! i can hear the relay turn on when I touch it to the chassis side of the brown/orange wire but it just doesnt send power to the blower! Was a frustrating dayu.

 

[franklin2]

Not sure what the relay mod is. Do they feed the motor directly from the battery with a relay? If so, then the original key-on power for the blower motor would be cut( the brown/orange) and this would go to the relay coil to trigger the relay. Then a good sized(10 gauge) wire would come directly from the battery with a circuit breaker or fuse, and run to the relay contacts, and then go to the other cut end left from the brown orange to feed the motor. This would feed the motor directly from the battery through the new relay.

Does this make that much difference? I supposed it may give you a little more speed, but it would add to the underhood clutter.

 

[typ4]

I did a 4 relay mod on the dually, takes all the load off the dash switch. Power and ground

 

[LCAM-01XA]

Relay mod, first you'll need to cut both blower motor wires, make sure you cut the orange/black wire on the dash side of the splice feeding the resistor pack (you want the relay between the splice and the blower speed switch, not between the blower and the splice). Then wire the relay as follows:

1. Blower positive:
a) terminal #85 = factory brown wire coming in from the harness
b) terminal #86 = added ground
c) terminal #30 = heavy gauge constant hot wire thru a big slow-blow (MAXI) fuse
d) terminal #87 = factory brown wire headed into the blower motor

2. Blower negative:
a) terminal #85 = factory brown wire coming in from the harness
b) terminal #86 = factory orange/black wire going towards the dash switch
c) terminal #30 = factory orange/black wire coming from the splice for the resistor pack
d) terminal #87 = good heavy gauge ground

Basically you use the factory brown harness wire to feed power both relays' trigger circuits when ignition is on. This will immediately engage the positive (blower power feed) relay due to the constant ground on its #86. The blower negative (high-speed ground) relay however only gets "primed" in a sense, to engage it still needs its trigger circuit complete which is what you do with the switch set to high in the cab.

Haven't tested this setup yet,try it out on your own discretion. Should work fine tho...

 

[Greg5OH]

So you guys thing i took the power to the blower (brown/orange) too far down? I basicaly cut it right near the blower plug.
i have to get to that factory splice (black cylinder) and tap in there? It would be between the rubber grommet at the plastic airbox and at the large junction where the splice is and the wires split off to the blower resistor?

Lcam, why is it necessary to run 2 relays?
The one basicaly feeds power to the switch, and the other feeds power to the blower itself?

 

[LCAM-01XA]

One relay feed power to the blower, the other provides blower with a short ground path when the speed switch is set to high by bypassing the miles of questionable factory wiring and so-so end ground points under the dash. Good power flow in and good ground make for little losses and a fast blower motor. Keep in mind the negative relay is only active when the switch is set to high, the three lower speeds still operate like the factory intended them to. Power feed is good for it all the time tho, and as a bonus it takes that 30-amp load out of your interior fuse panel (which is why I said make sure you fuse the thing well externally).

Not sure what you did when you wired your feed relay in. If you do it like I suggested it should be fine tho.

 

[Greg5OH]

thanks LCAM, i will try wiring it the way you suggested. I bet its me cutting after the splice (between splice and blower, not betwene blower and switch) that was causing the issues.
I am running an electric vacuum pump to control the hvac doors, pulls like .25 amps, but would like it to be on the relay circuit as well.
Should i hook it up to the blower positive circuit on terminal 87 as well?

Thanks.