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Old 03-07-2015, 08:28 PM   #1
lasmith03
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69 C10 Heater Wiring

I've got a non-AC 69 C-10. My heater isn't working.

My heater switch harness looks like this (pic from another post on this board):


But the brown wire that is shown in the wiring diagram on this board running from the back of the fuse panel to this harness at the heater switch does not do so on my truck. The brown wire instead goes to the ignition switch. (see the attached pic at the bottom...its the bottom wire in the pic below the two tan ones. BTW None of the wires are cut. I just wrapped them where the previous owner had shaved off the covering to test them.) I'm positive it is this wire. I stripped off all the wrapping and ran it back to the fusebox with it removed from the firewall.

Do I need to pull this brown wire out of the ignition switch plug and plug it into the empty 4th spot on the heater plug at the switch?

Thanks for your help. Here's the wiring diagrams.


http://farm4.static.flickr.com/3645/...c2a8064d_o.jpg

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Old 03-07-2015, 09:18 PM   #2
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Re: 69 C10 Heater Wiring

also having heater. Subscribed
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Old 03-08-2015, 12:13 AM   #3
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Re: 69 C10 Heater Wiring

Sorry double post, see next post.
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Old 03-08-2015, 12:18 AM   #4
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Re: 69 C10 Heater Wiring

[QUOTE=lasmith03;7080434]I've got a non-AC 69 C-10. My heater isn't working.

My heater switch harness looks like this (pic from another post on this board):


But the brown wire that is shown in the wiring diagram on this board running from the back of the fuse panel to this harness at the heater switch does not do so on my truck. The brown wire instead goes to the ignition switch. (see the attached pic at the bottom...its the bottom wire in the pic below the two tan ones. BTW None of the wires are cut. I just wrapped them where the previous owner had shaved off the covering to test them.) I'm positive it is this wire. I stripped off all the wrapping and ran it back to the fusebox with it removed from the firewall.

Do I need to pull this brown wire out of the ignition switch plug and plug it into the empty 4th spot on the heater plug at the switch?

Thanks for your help.

The brown wire you are seeing is the key switch accessory wire and it is a 12 gauge wire from the key switch shown in the first diagram below. It feeds the wipers the heater and the turn signal flashers. It is indicated by the first arrow on the left.

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Locate the heater switch on the diagram and you'll see another brown wire that is the feed wire to the switch. It is a 14 gauge wire and it comes from the heater fuse on the fuse panel up to the switch. You will have to run a new wire in place of it. You can't pull the other wire out of the key switch or you won't have any power for the accessories or the heater switch.

look at the fuse panel in the first diagram and you will see both brown wires on the left end of the panel.

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If you match the left side of the top diagram with the right side of bottom diagram visually, you can see how the wires match up and where they go.
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Old 03-08-2015, 12:54 AM   #5
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Re: 69 C10 Heater Wiring

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Originally Posted by VetteVet View Post
The brown wire you are seeing is the key switch accessory wire and it is a 12 gauge wire from the key switch shown in the first diagram below. It feeds the wipers the heater and the turn signal flashers. It is indicated by the first arrow on the left.
I know its hard to see, but the wire you are describing is the second wire in my pic (me holding the ignition switch connector top to bottom). Notice how the 24BRN/W joins it at the top. You can also see the 12P and 12PPL wires in my pic clearly which helps with orientation. Truck is metallic blue so there is overspray on some of the wires. Sorry.

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Locate the heater switch on the diagram and you'll see another brown wire that is the feed wire to the switch. It is a 14 gauge wire and it comes from the heater fuse on the fuse panel up to the switch.
This is the bottom wire in my pic. I think someone pulled it from the heater connector and plugged it in here. I traced this wire back from the bottom of the ignition switch connector (as I'm holding it in the pic) to the fuse block (the bottom left brown wire in the block diagram) and it terminates at one end of the AC fuse. I do not have a green wire that goes to the TEMP SW like in the diagram located on my ignition connector. Not sure where it is.

BTW, I have the gauges instrument cluster connector...not the dummy light cluster one. Maybe that's why I don't have a green wire there.
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Old 03-08-2015, 03:26 PM   #6
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Re: 69 C10 Heater Wiring

[quote=lasmith03;7080763]I know its hard to see, but the wire you are describing is the second wire in my pic (me holding the ignition switch connector top to bottom). Notice how the 24BRN/W joins it at the top. You can also see the 12P and 12PPL wires in my pic clearly which helps with orientation. Truck is metallic blue so there is overspray on some of the wires. Sorry.

This is the Accessory wire I referred to, it is a 12 gauge wire and it goes to the fuse panel for the wiper fuse the heater fuse and the turn signal flashers as you know. I thought that was the one you wanted to pull and run to the heater switch.

The 24 brn wire with the white stripe is the resistance wire for the alternator, external voltage regulator and it goes to the inside section of the firewall junction block. On the engine side it converts to a 16 gauge brown wire that goes to the regulator no. 4 terminal. These two wires are OK in the IGN switch plug. The large red wire is battery power and the purple is the starter solenoid wire. You'll have a pink wire which goes to the ignition coil. I know you know this but some of the viewers may not so I like to point it out.



This is the bottom wire in my pic. I think someone pulled it from the heater connector and plugged it in here. I traced this wire back from the bottom of the ignition switch connector (as I'm holding it in the pic) to the fuse block (the bottom left brown wire in the block diagram) and it terminates at one end of the AC fuse.

I see it and your description fits the heater switch wire. Here's how to tell.
Get a voltmeter and pull the brown wire off the IGN switch. With the positive lead on the wire and the negative lead on the nearest good ground, check for zero volts with the key off. Then turn the key on and check for 12 volts. IF you get 12 volts then pull the heater( AC fuse ) and check for zero volts. If you get zero volts then that's the heater switch wire. Without AC on the truck then that's the only wire that the fuse protects.


I do not have a green wire that goes to the TEMP SW like in the diagram located on my ignition connector. Not sure where it is.



Now we are going to get into a long explanation and you'll see how that ties into the brown wire being plugged into the IGN switch if that's what happened and I think it is.

The key switches had two extra terminals on them for the two lights in the cluster, labeled Temp and Brake warning. The idiot light cluster used both of those terminals. The double tan wires are for the Brake warning. One wire goes to the cluster connector shown in the first diagram to the number 2 pin labeled brake warning. The other tan wire comes from the master cylinder proportioning valve, through the firewall block and to the key switch. Those wires show up on your harness in your hand.

Now we get to the nitty gritty.
The light cluster had the Temp warning light in the cluster. It's wiring consisted of two green wires that were plugged into the key switch in the other extra terminal.

One of the wires goes to the light cluster to the number 5 pin on the cluster plug. The other green wire comes from the temperature sender in the left cylinder head and goes through the firewall block and up to the key switch.

The gauge clusters did not have the green wires to the key switch because they do not have the TEMP WARNING LIGHT.
Now you know why you can't find that green wire.

OK so here is why these wires went to the key switch.

When the factory engineers set up the wiring circuits they wanted to have a way to test the bulbs in the clusters, and this applies to the GAUGE cluster for the Brake Warning light as well.

Here is how it works.

When the key switch is turned on and it is turned to START, these two terminals, Green and tan, are grounded to the key switch body. This provides the ground side of the light bulbs and the power on the cluster board provides the positive side so the bulbs light. If you turn the key on, and go into the engine bay, and ground the sending unit wires the same thing should happen. Of course if you have the gauge cluster you won't see the TEMP light but the brake warning light should still come on.


BTW, I have the gauges instrument cluster connector...not the dummy light cluster one. Maybe that's why I don't have a green wire there.

Yes like I said above. If you compare the two connections in the first diagram, it shows the two connectors and the green wire goes to pin 5 on the left side of the light cluster from the key switch

The green wire direct from the sender goes to pin 6 on the left side of the gauge cluster without going to the key switch. The pin 5 is empty on the gauge cluster.

Just for the record you'll notice that pins 1 and 12 are empty on the light cluster connector and they have wires on the gauge connector.

These are the two wires that go to the battery gauge. There are other differences as well but they can be re-wired to convert from one to the other.



There is one problem with having the heater wire connected to the ignition switch at the green wire terminal. Remember I said that the green wire terminal and the tan wire terminals were grounded when the key was turned to start. This means that the hot brown wire would be grounded on start which would blow the heater fuse instantly. Was your heater fuse blown or blowing fuses when you started the truck? Some of the key switches would cut out the accessory circuits during the start cycle which would cut the power to the heater wire when the key was in start. I don't remember if the 67 to 72 key switches had that feature or not. If they did then the fuse would be dead during start and not blow.
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Old 03-10-2015, 11:38 AM   #7
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Re: 69 C10 Heater Wiring

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There is one problem with having the heater wire connected to the ignition switch at the green wire terminal. Remember I said that the green wire terminal and the tan wire terminals were grounded when the key was turned to start. This means that the hot brown wire would be grounded on start which would blow the heater fuse instantly. Was your heater fuse blown or blowing fuses when you started the truck? Some of the key switches would cut out the accessory circuits during the start cycle which would cut the power to the heater wire when the key was in start. I don't remember if the 67 to 72 key switches had that feature or not. If they did then the fuse would be dead during start and not blow.
VetteVet thanks for all the help!!! I crawled under there and looked at it again yesterday. I'm positive that the brown wire in the iginition is the heater wire now because the length of this wire is way longer than the other wires in the loom (plus I ran it back to the fuse block like I said). The PO must have plugged it in there incorrectly when wiring back up the truck. I'm going to move it over to the heater. I'll let you know how everything goes once I have got everything put back together. I'm also sorting out the wiring harness under the hood (burnt frayed wires). PO put in an HEI distributor and a one wire alternator and evidently didn't do it right the first time.

I'll post an update once its all finished.
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Old 03-22-2015, 11:37 AM   #8
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Re: 69 C10 Heater Wiring

I removed the brown wire from the ignition and put it in the heater wiring harness. Heater works now. PO had already replaced the blower motor so its all good to go. Thanks VetteVet!!!
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Old 03-22-2015, 11:45 AM   #9
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Re: 69 C10 Heater Wiring

You're very welcome
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Old 05-05-2016, 05:19 AM   #10
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Re: 69 C10 Heater Wiring

Hi , iam am having a similar issue. i have the brown wire that plugs into the heater but theres no power from it. today i cut the brown wire and connected a 12 volt battery to it and the fan worked perfect. can i connect the fan directly to the fuse box?
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Old 05-05-2016, 11:00 AM   #11
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Re: 69 C10 Heater Wiring

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Hi , iam am having a similar issue. i have the brown wire that plugs into the heater but theres no power from it. today i cut the brown wire and connected a 12 volt battery to it and the fan worked perfect. can i connect the fan directly to the fuse box?
Well Ben, I am not sure what you are asking but it seems that you want to run the brown wire from the fan motor directly to the fuse box. If that's the case then you can do that, but the fan will run anytime the key is on, and you won't have any slow or medium speeds.

On the back of the fuse panel behind the heater fuse, there should be the brown wire connected, which should run straight to the fan switch to the common terminal. then there are three wires from the switch which run to the blower motor resistor and from there you'll have one orange wire which goes to the fan motor through the firewall for it's power. Jumping this wire to a 12 volt source will make the motor run in high speed. That's how I check them if I suspect that the fan motor is bad.
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Old 05-05-2016, 04:09 PM   #12
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Re: 69 C10 Heater Wiring

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Well Ben, I am not sure what you are asking but it seems that you want to run the brown wire from the fan motor directly to the fuse box. If that's the case then you can do that, but the fan will run anytime the key is on, and you won't have any slow or medium speeds.

On the back of the fuse panel behind the heater fuse, there should be the brown wire connected, which should run straight to the fan switch to the common terminal. then there are three wires from the switch which run to the blower motor resistor and from there you'll have one orange wire which goes to the fan motor through the firewall for it's power. Jumping this wire to a 12 volt source will make the motor run in high speed. That's how I check them if I suspect that the fan motor is bad.
Hi VetteVet
Thanks for the reply,
the brown wire I have now comes from the wire loom, and looks also like it goes through the ignition. However there is no power coming through it, when key is on or on acc.
So yesterday I cut the brown wire and striped the coating back. I plugged the wire with the spade end into the black connector and then plugged the connector to the fan switch on the lever controls.
I took a 12volt supply and attached it to the stripped end of the cut brown wire, to simulate power through that wire as per what would normally happen, an attached the earth to the dash. The fan worked perfect, with all speeds and controls.
So the question is,
Can I make a new brown wire and attach it to the back of the fuse panel heater fuse, and go direct to the fan switch in the same position as the cut wire that I tested and bypass the origanal wire in the loom and ignition?
I hope that makes sense, I will post pics if I can
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Old 05-05-2016, 06:09 PM   #13
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Re: 69 C10 Heater Wiring

Attached is the setup i did to make it work, also a photo of the ignition. as you can see, its a bit of a birds nest. PO installed a engine immobilizer and they seemed to cut allot of wires, that's why i believe i have no power through original brown wire.

what do you think?
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Old 05-05-2016, 11:09 PM   #14
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Re: 69 C10 Heater Wiring

Quote:
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Hi VetteVet
Thanks for the reply,
the brown wire I have now comes from the wire loom, and looks also like it goes through the ignition. However there is no power coming through it, when key is on or on acc.
So yesterday I cut the brown wire and striped the coating back. I plugged the wire with the spade end into the black connector and then plugged the connector to the fan switch on the lever controls.
I took a 12volt supply and attached it to the stripped end of the cut brown wire, to simulate power through that wire as per what would normally happen, an attached the earth to the dash. The fan worked perfect, with all speeds and controls.
So the question is,
Can I make a new brown wire and attach it to the back of the fuse panel heater fuse, and go direct to the fan switch in the same position as the cut wire that I tested and bypass the origanal wire in the loom and ignition?
I hope that makes sense, I will post pics if I can
That sounds like what I said to do and if it works and it's fused you're golden.

That wiring looks pretty rough but as long as it's safe and you understand it you should be fine. VV
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Old 05-06-2016, 01:04 AM   #15
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Re: 69 C10 Heater Wiring

Thanks VV
i will try that tonight.
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