Voltage drop in cab with load (blower motor)

[dunk]

''

 

[daazedjmcfarland]

I have noticed the same on an 84. It's mostly just old wire and old connections. Definitely running some 8 gauge would help and cleaning up those fuse box connections. But, the biggest thing you can do is put the 3g alternator in there and re run some 1/0 grounds and hot wire. I had to do this because of the speaker system I put in and I was worried about the draw from the electric lifter. It is actually way easier than you might think it is. Hardest part was getting the damn pulley off of the old alt

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[FORDF250HDXLT]

voltage drop in the cab with the heater blower on
maybe there are better options

the biggest thing you can do is put the 3g alternator in there and re run some 1/0 grounds and hot wire.

summarized with everything you need to focus on.
the 3g upgrade is one of the first things i would do to a pre '92.5 idi engine before she hit the street fwiw.

 

[typ4]

Blower relays to take the load off the dash. Did both trucks. Huge difference

 

[CDX825]

From what I recall power is fed to the blower motor. Then the ground side of the motor runs to the resistor block and the actual blower switch grounds the different taps of the resistor to adjust the speeds.

If this is the case you could easily use three relays for each speed and reverse the way power flows from factory starting with the relays. The relays would all be fed ignition switch power to one side of the coil. the other side would be grounded by the switch. Power feeds in to the relays then out to the resistor block for each speed. High doesn't use the resistor so its just straight to the motor. Then the motor has a constant ground instead of being switched.

That's the way I want to do mine so none of the load is on the dash side including the ground. So the dash switch is only has to carry the load of the relay coil.

 

[daazedjmcfarland]

I know this may be off topic but could you wire a dimmer switch for the fan control?

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[typ4]

I use 4 relays, power, low,med,high. At least do 2, power and high, it puts the most current through blower switch. No on the dimmer.

 

[bbjordan]

Check your blower motor to see that it turns freely. On my '91 I had to lube up the bearings. I used ATF.

 

[daazedjmcfarland]

You can't use an actually dimmer switch but you can use one that is similar called pulse width modulation (pwm switch) www.ebay.com/itm/like/262095693251?...7290-0%26rvr_id%3D1108312820281&ul_noapp=true

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[daazedjmcfarland]

They aren't really meant for blower motors but I build PCs and they give you speed control on the fans....you'd just need a 20a or 30a one...not sure what kind of draw these blower motors have

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[BDCarrillo]

Should be easy with a potentiometer and 555 timer running a big transistor. That'd also be a good way to divorce the motor and dash wiring.

Great, another side project lol...

 

[laserjock]

I'll leave this here.

Leadrise[emoji768] 10-50V 60A DC Motor Speed Control PWM HHO RC Controller 12V 24V 48V 3000W MAX https://www.amazon.com/dp/B00YGTB3NO/ref=cm_sw_r_cp_api_a1V.xb8GPSSMP

Now, if you could use the blower resistor in place of the pot to give you the three speeds. [emoji6]

 

[FORDF250HDXLT]

Check your blower motor to see that it turns freely. On my '91 I had to lube up the bearings. I used ATF.

^ i would suspect this too.perhaps it's just bad.im all for taking the load off a switch and putting it on a relay.even if it's just for high speed.however the load it's pulling,is the load it's pulling.with a 3g alt, a blower motor shouldn't mean a thing,let along a noticeable voltage drop.

 

[ifrythings]

The thing that everyone is missing is the fact that almost everything in the cab is ran off of one power wire through ONE pin on the firewall plug, the exact same pins used on the glow plug harness that likes to melt. They changes this on the 92 and up trucks but if you really want to see a difference run a big 8,6 or 4 awg wire from your starter relay right to the yellow wires on the ignition switch and you'll see a difference.

For reference, large yellow wire runs almost everything in the cab

Black/orange runs the lights and a few other smaller things

Small yellow wire goes the the brakes and hazard lights

Those are the main power wires into the cab upto 1991 (maybe different a bit for 80-86)

Only thing left after that is to relay the ignition switch.

Edit: to add to this, the ground system in the cab isn't done the best, ford grounded everything to the metal dash frame which is then bolted to captive nuts on the a pillar which is still nicely painted, grounding the dash to a nice solid clean ground will help also.

 

[ifrythings]

Not 100 percent sure on the 80-86 but if they are the same like 87-91 then it will be up around the ebrake release lever.