Electrical help with heater blower on '78 SA FJ (1 Viewer)

Cromagnon

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It appears you have a wiring problem. Somehow you are getting 12V on the WB wire. As I said earlier that needs to be ground. It looks like if you correct that then the circuit will behave as expected. Do you have WB wired to the heater switch? That would be the first place I would look. Pictures of the connectors and the wire colors would be helpful at this point.
 

Cromagnon

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When I plug the blower back into the circuit that is when it will run with the engine OFF but as I turn the key to ON I lose power.
You aren't losing power, there isn't any difference of potential between the switched leads and the 12V on the ground. If the blower motor were grounded to the chassis you would be blowing fuses or have melted wires and a fire.
 
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Here is a photo of the fan pull switch and the plug I found under the dash. I can't really get any better view of it or the wire color.

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I thought maybe I had installed it backward but there is only one way to attached the switch to the under dash plug.
 

Cromagnon

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The female receptacle in your hand has what color wires going to it?

The switch has four wires, LR, LB, LW and ??, going to a male plug. The wiring diagram that I have shows three wires going to the heater switch, LR, LB and LW. If the there is a second LB wire, it would go to the rear heater.

The wiring diagram also shows the WB wire at the blower motor goes directly to ground. That needs to be confirmed as well.

With everything disconnected, the motor off and the key in the ACC position, do you see voltage on the LR wire at the receptacle in your hand?

With everything disconnected, the motor off and the key in the ON position, do you see voltage on the LR wire at the receptacle in your hand?
 
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Guys:
Apologies for not getting back quicker, winter arrived early up here in Idaho with the FJ taking a lower priority. The heater I bought came with a fan switch had been over sprayed with blue body paint. I can't be sure what color the wires are. All the household cleaners, paint thinner, scotch bright, and 80 grit paper isn't taking the blue paint off. Any ideas without damaging the wire?

Thanks, Craig

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TheHardWay

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The blue color isn't paint:
Heater switch_LI.jpg

So you have two blue/black wires, one blue/red and one blue/white coming out of the switch - correct per 78 electrical schematic. Stop scrubbing!
 
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Guys:
Good afternoon.
Here is my table for the plug up under the dash based on the wire colors listed above on the fan pull switch. Even with the key in the off position there is 12v on the blue red wire and the lower blue black wire.
Craig

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Cromagnon

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The LR wire is fed from the 15A Heater fuse which is only supposed to have voltage with the switch in the "IG" position. Confirm that this is happening. Someone may have performed some wizardry on your fuse block.
 

Cromagnon

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There should be a legend on it for the wire colors. The heater circuit is fed from the IG position of the ignition switch. It seems like someone has messed with the feeds on the fuse block.
 
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Looks like a red wire to one side of the 15A fuse and yellow/black wire from the other side of the fuse to the IG.
Do you suspect the is a jumper? Not sure what I should be looking for.
 

Cromagnon

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If it doesn't have a factory color coded wire then it is something that was put there by an electrical wizard to perform some magical feat. Without a picture and going by your description there is no way to know.

If you look at your wiring diagram you should see a BY wire from the IG position of the ignition switch providing power to (feeding) three fuses, Engine, Heater and Turn/Wiper. You need to verify that the BY comes from the ignition switch. If there is a R wire and a YB wire those are not factory installed and you will have to validate what they are for and determine why they were put there. If it were my vehicle I would put the wiring back to factory as that is the easiest way to troubleshoot it in the future.

Use your wiring diagram and a multimeter to verify, validate and troubleshoot your wiring problems. This will not be easy and takes time. The easiest way would be to pull the harness out, put it on a board, troubleshoot and restore it back to factory and then reinstall it.
 
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Thanks I do agree. As fortune would have it I bought a new fuse block months ago just thinking I would use the cover. Now it feels like maybe I should go through the effort of putting in a new one while also getting the factory wiring corrected. How difficult is it to access the ignition switch to be able to see the wire colors?

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