Yes, I did replace the blower relay (on the firewall beside the blower motor.) Worked fine through 3 ignition switch on/off cycles. On the 4th cycle, the blower stayed with the ignition switch turned off. Same problem I started with.

Still getting power to the Heater fuse (Fuse 6) with the ignition switch in the off position (key out.)

 

Yes, I replaced the blower relay with a new one. Problem on-going.
Blower turned off first 3 ignition on/off cycles, then blower motor continued running after the fourth (and subsequent) times I turned the ignition switch off.

Still getting power to the Heater fuse (Fuse 6) with the ignition switch off.

 

Pull fuse 6 when the blower has failed on with ignition off and probe the two fuse sockets with a volt meter to see if 12v is found upstream towards the ignition switch or downstream towards the hvac control unit.

Has the ignition switch ever been replaced?


George

 

Ignition switch replaced 4 to 6 weeks ago as the initial "fix" for the problem. When that didn't work bought another switch with a different part number. (Both were listed for my vehicle. Hoping maybe the pin-outs were different. They weren't.)

I will probe fuse 6 for voltage tomorrow (Tuesday).

I have probed fuse 6 with a "computer safe" probe, The upper fuse socket is getting power but I'm not sure that it is a full 12 volts.; the lower fuse socket is going to ground. Not sure which is upstream. I have located to heater switch feed wire (brown, 12 ga), but I can't see it well enough to determine whether it is connected to the upper or lower fuse terminal. I can back probe the ignition switch connector to see if any hot-in-run wires are hot with the ignition switch off. Looks like there are only 2 wires from the switch designated as hot-in-run.

OK. Found the fuse box diagram (below). Per the earlier schematic I sent, power exits the fuse-box via n7, so that would be the downstream terminal. 6 columns, 4 fuses, 8 rows. That implies that m8 is the corresponding terminal for n7 ( fuse 6.) Therefore, the upper terminal is the upstream and is getting power. I will check the voltage later today. (I have included the above so that you can double-check my logic.)

Again, thanks.

 

It sounds like you have confirmed that the power with the ignition switch off is coming from the ignition switch side (m8). So you had this exact problem, replaced the ignition switch and still have the same problem, is that correct?

There are four wires from the ignition switch that supply “power in run”. Orange, brown, pink and pink/white. We are interested in orange. Yes back probe that wire when the blower will run and the ignition switch is in the off position. Pull the #6 fuse for this measurement after you confirm the faulty operation.

If you have power on the orange wire then it would be natural to condemn the ignition switch but you already replaced that and the odds of a new one failing in the exact same way are very low so I am not so sure that’s the problem. The other possibility is a short/corrosion somewhere causing power to back feed onto this wire. Have you ever had the ip fuse panel out to see the condition of the back side of that panel? Have you ever seen wiring damage or corrosion anywhere around these circuits? Using my power feed wiring diagram you can pull the other three fuses and breaker to see if power remains on that wire with the ignition switch off.

In order to absolutely condemn the switch you would have to uncouple its connector and confirm continuity from orange to the power feed into the switch (red) when the switch is off. This could be a little tricky since the problem is intermittent.


George

 

Ready for a curve ball?
I pulled the cruise control fuse, and the heater fan now works like it's supposed to - with the heater switch/fan on and ignition switch in run, the fan runs. Turn the ignition off, and the fan stops.

Got to looking at the fuse box diagram I sent yesterday/this morning and saw that, if my fuse box bus bar theory was correct, the only other circuit on the bar was fuse #12, which handles power to the cruise control. Figured that I'd pop that fuse prior to start probing. (Much easier.) Anyway, it solved the heater fan problem - at least for about 8 on/off cycles of the ignition switch. Turned the cruise control switch (on the turn signal lever) off , reinserted the fuse and blower still turned off with ignition. switch. Turned cruise switch back on, turned switch on, heater fan ran. Turned ignition switch off, heater fan stopped. Same results with cruise on and hitting the "accel" swith on the cruise control, i. e., fan turns off with ignition switch

My guess that I have a faulty relay in the cruise control system, back feeding the fuse box. The relay is only activated when the cruise control is actually engaged; have to be moving at 25+ mph for it to actually engage. Pulling the fuse (or disconnecting the battery) reset the relay. (This doesn't eplain why the problem reappeared 3 ignition cycles after replacing the blower relay and reconnection the battery yesterday.)

The truck won't be drivable for a day or two (at least), so I can't test the theory till then. Meantime, I'll pull down cruise control schematics to see what they look like. I'll monitor and update the thread with the result of the test drive and/or find the elusive stuck relay.

Thanks again for your help and your patience.

 

It's not a curve ball at all, that's why I asked you to pull the other fuses and breaker in that power distr diagram that I posted earlier which includes fuse #12. This confirms that there is nothing wrong with your ignition switch and one of the components on that power circuit from the switch has a short to power downstream of fuse #12. There are no additional relays or buss bars, just splices. This is why we do this level of diagnostics, to avoid the parts cannon and in this case, another ignition switch. We have work to do because 5 things are powered by that leg and we need to find the short to power. You may want to get a look at the back of that ip panel before we start the new leg of this adventure because windshield or door leaks can cause corrosion back there.


George

 

Here is your new treasure map showing the wiring, splices and 5 modules on that circuit:





George

 

BTW, one of the reasons I suspect the back of the IP fuse panel is that the # 6 and #12 fuses are next to each other.

George

 

Quick question on site mechanics. How do I attach/embed schematics, pinout drawings, etc into a post? Last night I copied and pasted a fuse panel pinout diagram (from AllDataDIY site to my post - looked good prior to sending. Today, the post has a picture of camshaft brackets -. Evidently, I'm doing something wrong.