Guest reerunclassics Posted November 7, 2010 Share Posted November 7, 2010 Me and my son put a 1971 Buick Skylark back on the road this year but have an issue with the heater blower motor getting constant power and shorting them out. In the engine compartment we've changed the engine harness, the relay switch, the resistor. Inside the dash we've changed the fuse's, checked the fuse block for short's, changed the ignition switch, and still with the key off it still has a constant stream of power going to the heater blower motor. Any ideas? Please help, it's his daily driver and cold weather's comming.:confused:reerunclassics@hotmail.com Link to comment Share on other sites More sharing options...
BUICK RACER Posted November 7, 2010 Share Posted November 7, 2010 Did you check the blower switch? They can melt and short out!? Link to comment Share on other sites More sharing options...
Guest reerunclassics Posted November 8, 2010 Share Posted November 8, 2010 Checked the switch today, uncoiled the harness, everything checks out fine but still when I connect the battery the blower motor runs full blast. I'm 100% out of ideas, I've checked everything known to check.:confused: Link to comment Share on other sites More sharing options...
NTX5467 Posted November 8, 2010 Share Posted November 8, 2010 For the fan motor to run at "full speed", that would mean that the blower motor is wired direct, somehow, and bypassing the switch in the a/c-heater control panel PLUS the blower motor resistor under the hood. In some cars, there is a "High Blower Relay" which automatically is used to keep the blower switch inside the car from cooking due to higher voltage running through it on the "HIGH" blower speed. Usually, the blower motor relay is under the hood near the blower resistor in the HVAC case.In the way that GM does their wiring harnesses, under the hood, there will be: a Front lighting harness, an Engine harness (ignition system, basically), the air conditioning/heater harness (a/c compressor, throttle kicker on the carb OR anti-dieseling solenoid, and the blower motor harness), a charging system harness, and maybe another one. EACH has its own purpose and they generally don't mix BUT they can reside next to each other. Similar with inside the passenger compartment. What might be considered to be one harness is actually several different harnesses for particular functions in that area of the vehicle.IF you used a Painless Wiring harness (or similar), I believe they usually use factory GM wiring codes to make their products work for many different vehicles. My observations have been that GM wiring color codes did not change that much over the years--if at all--at least in the era of your vehicle. Therefore, you might need to invest in a GM service manual for the vehicle to ensure that how you did things is compliant with factory orientations in ALL cases. It could be something as simple as a ground that was missed, allowing for voltage to back-feed as it has no other place to go in particular situations. Hopefully, the inner and outer sections of the fuseblock bulkhead connectors have wiring color codes that match each other?In general, though, the part of the harness you'd need to be concerned with would be the "A/C and Heater Wiring Harness". That would start with the basic feed through the firewall connection . . . going through the main ignition switch feed to the blower motor switch feed, which would then make it a "switched feed". The blower motor switch would then send the current to one of the blower motor resistor sections, and then to the blower motor. It is the sections of the blower motor resistor which make the different blower motor speeds rather than the blower motor switch itself. As mentioned, the blower motor relay can be in the circuit too.As Roberta mentioned, sometimes the blower motor switches can fail internally, but from my observations when they do fail, the "feel" of the switch becomes different as the internal detents between the speeds will be degraded or completely absent.Keep us posted on what you find.NTX5467 Link to comment Share on other sites More sharing options...
Guest reerunclassics Posted November 8, 2010 Share Posted November 8, 2010 Thanks NTX5467 for the great reply. I have found one relay switch on the fire wall and one under the dash and have replaced both with new ones. I unwrapped the ac/heater harness to check for shorts and re-taped it. I have double/triple checked all grounds. As far as I can tell I've narrowed it down to the fuse block or the dash wiring harness. I guess my next step is to get some schematics for the dash harness and go from there. Take Care,Rob Link to comment Share on other sites More sharing options...
JohnD1956 Posted November 9, 2010 Share Posted November 9, 2010 Assuming NTX 5467 is correct, that the wiring did not change much on cars of a particular era, I just looked in my 69 Service manual and one possibility is a short between your voltage regulators # 4 terminal ( Brown wire) and the orange/blk wire going to the heater motor. These two wires go through the body electrical harness on adjacent ports. If you have any rust issues on your cowl in this area, or a leaky front windshield, I'd recommend pulling the fuse panel off and separating the body harness to clean and ensure the terminals are not compromised. And by way of information, inside the car, it appears there is a #14 brown wire which goes from the fuse to the blower switch. This might have been compromised by someone, at some time, with the #10 Brown wire coming from the ignition switch to the fuse panel. Also, under the hood there is a second orange/blk wire going to the wiper. Although the same color, these two wires have different paths and ports and are not intersected as far as I can tell. Good luck. Link to comment Share on other sites More sharing options...
Guest reerunclassics Posted November 10, 2010 Share Posted November 10, 2010 Went to the salvage yard today, pulled another switch, noticed there is a ground wire that runs up into the main harness that connects to the back of the heater control unit. The harness on my son's car does not have that ground wire. I grabbed an extra wire and connected to the back of the unit and touched it to several other grounds but no change. As soon as I connect the battery the blower motor zooms full speed, key's off and out of the ignition? I'm at a complete loss? Link to comment Share on other sites More sharing options...
BUICK RACER Posted November 10, 2010 Share Posted November 10, 2010 This may be a silly question, does the car start ok and run ok, otherwise? Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted November 10, 2010 Share Posted November 10, 2010 Not simple but obvious something is cross wired. Did you ever get the wiring diagram? I would start at the fuse block and pull heater blower fuse and see what happens. Ben Link to comment Share on other sites More sharing options...
Guest reerunclassics Posted November 11, 2010 Share Posted November 11, 2010 I've got a color diagram comming in, hopefully in the next day or two. I considered pulling the heater fuse but I've tested the fuse block and with the ignition off there's no power going to that side of the fuse block. Car runs fine, everything works great. If I could just get this crazy heat issue fixed my son would have a great car. Winter has hit the salt lake area, were in the 40's for highs 20's for lows and with no defrost in the moring the car is now parked until we can get this fixed. Going to pull the fuse block again tomorrow and start over.Thanks,Rob Link to comment Share on other sites More sharing options...
BUICK RACER Posted November 11, 2010 Share Posted November 11, 2010 Here's your schematic!http://www.teambuick.com/reference/library/71_chassis/files/120-g-color.pdfI had a similar problem with a '73 Century, the fuse would blow for the power window and direction signals. I used a tool similar to this:Tool Aid (SGT25100) Short Finder The short was the air cleaner hitting the hot lead on the anti-diesel solenoid, who would have thought that! Link to comment Share on other sites More sharing options...
Guest reerunclassics Posted November 13, 2010 Share Posted November 13, 2010 Got a color wiring diagram in yesterday, traced every wire in the dash harness and all wires in the engine compartment. Nothing broke or burned, everything connected to where it's supposed to, yet the heater blower motor still runs full high as soon as I connect the battery.Going to see about pulling a harness from another car today and see what happens. Link to comment Share on other sites More sharing options...
Guest reerunclassics Posted November 14, 2010 Share Posted November 14, 2010 Went to the salvage yard today, pulled a complete dash harness, so now I've replaced the engine harness and dash harness and still have the same problem. Heater blower motor runs full on when I connect the battery. I'm completely out of idea's, every relay, blower motor switch, light switch, voltage reg, resistor has been changed, this ones for the record book... Any ideas?Take Care,Rob Link to comment Share on other sites More sharing options...
Guest reerunclassics Posted November 14, 2010 Share Posted November 14, 2010 Went to the salvage yard today, pulled a complete dash harness, so now I've replaced the engine harness and dash harness and still have the same problem. Heater blower motor runs full on when I connect the battery. I'm completely out of idea's, every relay, blower motor switch, light switch, voltage reg, resistor has been changed, this ones for the record book... Any ideas?Take Care,Rob Link to comment Share on other sites More sharing options...
old-tank Posted November 14, 2010 Share Posted November 14, 2010 Start again at the blower motor and if no joy just rewire it as if it were an add-on accessory. 1 Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted November 14, 2010 Share Posted November 14, 2010 Yeah, Willie, that is what I would have done already, But would be interesting to determine the actual culprit. Ben Link to comment Share on other sites More sharing options...
rick60 Posted November 15, 2010 Share Posted November 15, 2010 Did you try disconnecting components one at a time? Make sure all grounds are secure. It is also possible that you replaced a defective part with another defective part. Just because a part is new does not mean it is good. This sounds like a shorted high blower relay. I would not rewire the motor. Link to comment Share on other sites More sharing options...
NTX5467 Posted November 16, 2010 Share Posted November 16, 2010 With all due respect, since this is a GM vehicle which usually didn't have any issues with wiring harnesses, it would be best to make sure everything is as is should be, even if it seems to be. Something's gotten bypassed in there, somewhere, or the blower motor switch would be functional, as designed.I understand Old-Tanks' orientation and there should be a "switched" voltage terminal on the inside section of the fuse block,which is open for use, that could be a good voltage source to go to the fan switch. BUT I would consider that to be a last resort situation.In THAT realm of thought, as you have the wiring schematic which shows the voltage feed to the rear of the blower motor switch, what happens if you put 12V directly to that terminal and then try to modulate the fan speed with the switch? For this, you could use an auxilary voltage supply rather than battery voltage from the vehicle. This should test that particular circuit ONLY (my theory is to ground the aux power source to the body and then use the power side to the particular terminal. To do this best, you might need to get some terminals and make some short jumper wires so that you could pull the connector off of the switch and then better attach the aux power to the appropriate power feed terminal on the switch. I would think that with the aux power, if things worked normally, then there's something flaky in the harness somewhere.An additional thought . . . on some years of GM vehicles, when the a/c control is on "MAX" the fan runs at top speed anyway, unless you unplug the wire to the switch and a/c control switch that makes that happen. I don't think that's on your model year of car, though.Just some thoughts,NTX5467 1 Link to comment Share on other sites More sharing options...
Guest reerunclassics Posted November 17, 2010 Share Posted November 17, 2010 Finally figured it out. The new relay switches from the parts stores have the points inside to close together. They need to be spaced out. I have one from NAPA, AutoZone, and Checker Oriley and they all have the same problem. It was a costly venture chasing this problem but glad it's over. Thanks to everyone for the advise in helping me solve this.Take Care,Rob Link to comment Share on other sites More sharing options...
buick5563 Posted November 17, 2010 Share Posted November 17, 2010 Glad you figured it out. 1 Link to comment Share on other sites More sharing options...
NTX5467 Posted November 17, 2010 Share Posted November 17, 2010 Thanks for the update! I might suspect that all of those switches (from the auto supply stores) all came from the same manufacturer, just in different boxes and markings for the different stores)--just a gut suspicion.Glad you got it taken care of!NTX5467 1 Link to comment Share on other sites More sharing options...
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