[VetteVet]

[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.