Hello -

I apologize in advance for the long post, but I wanted to give as much information as possible.

I have owned my 70 Chevelle for a couple months now, and I am just starting to try to get the A/C working again. When I switch the blower speed from high to any other speed, the engine shuts off. It will crank, but it won't start indicating that the ignition system isn't getting any current. Everything works perfectly if the blower is on high or off, but if the blower is on any other speed, the ignition system is dead. This car has an Excel 1 piece self contained ignition system (coil in the distributor) that the previous owner installed. When I unplug the connections to the blower motor resistor, I can have the blower switch on one of the other speeds without the car shutting off, but the blower is obviously not getting current or working at this point because the resistor is unplugged.

This car had/has some electrical problems (most of which I have already corrected) but this one has me stumped. I have replaced the forward lamp harness and the A/C harness. I have a new engine harness, but I haven't replaced the old one yet. The previous owner replaced the dash harness. I have also replaced the blower motor speed switch and the blower motor relay that sits on top of the evap box. I'd like to replace the blower resistor, but I can't find one anywhere for a with A/C car. If anyone has one of these for sale or knows where I can get one, please let me know.

When I first got the car, it had a lot of electrical problems. The A/C compressor is missing so I never tried to use the blower until a couple weeks ago on vent. The blower would not work at any speed. I took the dash pad off, and it looked like all of the dash wiring had been replaced except for the A/C harness so I went ahead and replaced it along with the blower motor switch (which was burnt) and the blower relay. I wanted to replace the blower motor resistor, but I haven't been able to find one yet. The old A/C harness was probably ok, but I wanted to replace it anyway. It looked like the blower motor not working was either caused by a burnt switch or the previous owner not knowing to hook the A/C harness to the dash harness when he replaced the dash harness.

The blower now works on all speeds with the car not running and the ignition switch in the on/run position. The high speed is blowing at a reasonable rate, but all of the other speeds seem almost non-existent, which is why I'd like to replace the resistor. Up until today, I had only tested the blower while the car was off. Today, I was driving and had the controls on vent with the blower set to high. I switched to a lower speed and the engine shut off (while running about 80 down the Dallas North Tollway...). The engine shuts off and will crank but not start when any other speed than high is selected. The car will not re-start until you either select the high speed or turn the A/C off all together.

I would appreciate any help or ideas anyone may have on this topic.

Thanks,

Brian Schultz
ACES #8085
1970 Chevelle SS396
1966 Impala SS
2003 BMW M5
2000 GMC Yukon

First, how is the ignition system wired? Is your Excel 1 piece self contained ignition system using the original resistance wire?

Hi Greg,

Thanks for the the reply. Two wires are connected to the Excel housing. One wire is green (medium or light green) and the other wire is dark brown. The green wire comes out of the engine harness and the brown wire comes through its own hole in the firewall. I'm assuming the brown wire is for the tach. I can't find a green wire on my wiring diagram on the engine harness so I'm not sure if this car may have an engine harness from a 71 or 72 instead of a 70. The A/C harness was from a 71 or 72 before I changed it out. The engine harness is the only underhood harness I haven't changed yet. I have a new one, but I haven't changed it yet. Folowing the engine harness from the bulkhead, the wiper wires are all correct, next is the mysterious green wire and a lead going over to the electric choke on the carb, then after that there is the normall stuff...TCS disconnected, etc. According to my 70 diagram, Im supposed to have a yellow coming from the starter solenoid up to the coil and a white/orange/purple wire from the bulkhead to the coil. Any ideas?

Thanks again,

Brian

I dug a little deeper here and founf that after unraveling some of the electrical tape that the light green mystery wire is actually spliced to both the yellow and the fabric covered white wire. The brown wire is definitely for the tach. I'm guessing from this that the previous owner just used the two wires that originally connected to the + side of the coil, spliced them together and connected them to the Excel unit.

Brian

I believe you have a combination of problems. I am not familiar with the Excel unit, is it a HEI or a converted points distributer? If converted, does it require reduced voltage or full system voltage? The cloth covered wire is a resistor wire, and reduces voltage to the coil when using a points distributer. It shouldn't be used with HEI's and most other ignition systems. The blower high speed is fed directly from the horn relay through the high speed relay, the other speeds from the fuse box, but through ignition switch. Your problem is most likely excessive voltage drop to the ignition. It is probably still getting power, just not enough to for the car to start. Check connections at ignition switch (pink wire feeds ignition system) and determine if resistor wire needs to be replaced.

Hi Greg,

I have done some other digging since last night, and it looks like the previous owner spliced a couple inches of wire on the end of the original resitor wire to make a spade terminal to connect to the Excel unit. The Excel unit is HEI for sure so I'm guessing it's only getting 9 volts. I have a brand new factory reproduction engine harness from Lectric Limited that I was going to install (it came with the car). It looks factory correct, but it's set up for points with the standard resistor wire and yellow wire spliced together. Can I un-wrap the harness and replace the resistor wire with a 12g wire from the bulkhead forward? What do I do with the yellow wire? It makes sense now that using the other blower speeds is robbing the already starved HEI system so I'd like to fix it right without buying another harness that's already been converted to HEI. I'd like to use the new harness I have since the one in the car is hacked up. Any help you can provide on how to convert my new harness would be much appreciated.

Thanks again,

Brian

Sounds like you are getting it sorted out. Some A/C info. A 70 Chevelle A/C harness is different than a 71-72. In 71-72 You will find 2 relays under the glove box. What do they do? When you shut off your 71-72 Vell and the key is in your hand, Sit in the car with the key you just pulled out of the Ign.(BE QUIET)The key is in your hand. You will hear a "Click".
This is a anti DIESELING system used in 71-72. When you pull the key out of the ign. this applys power to one relay, inturn it supplys 12 Volts to the A/C clutch for 3-5 seconds to load the engine to stop the engine from being a diesel. I built a 70 Red SS 454 Sta. Wgn.(driver)
It was a 71 body with A/C, It is now a 70. After the car was built and running with a Green 70 SS dash, That is when I found out a 71 A/C harness will not work with 70 under hood 70 under dash. NOW I had to pull the dash and install a 70 A/C harness. Not a good idea to mix different year wiring harness!!!!!!!!!!! Bob ACES--AACA

Hi Bob -

Yes, this car did have a 71 A/C harness when I got it, but I changed that immediately along with the hacked up forward lamp harness. The dash harness looked new and correct so I didn't mess with it. I am in the process of removing the resistor wire from my new engine harness and replacing it with a 12g standard wire. I just love this black stick crap that I'm getting all over everything...lol. I'm hoping that this will ensure that I get full voltage to my HEI, and I'm hoping that solves my blower to engine shut off connection.

Thanks,

Brian

Hello All -

I modified my new engine harness (changed the resistor wire to a standard 12g wire) and installed the harness. I am still having the same problem (any fan speed except high shuts the engine off and prevents it from starting. The engine starts a little quicker though now that the HEI has full voltage. I installed the engine harness the same way as the old harness. Windshield wiper wires hokked up normal, jumper wire to carb, new 12g wire and yellow wire connected together and connected to the HEI, oil press wire connected to sending unit, black and orange wires hokked up to TH400, purple wire to solenoid, yellow wire left unhooked as this was the way it was before, orange blower wire for non A/C cars left unhooked, and all TCS wires left unhooked. Will not hooking the yellow wire up to the other solenoid post cause any issues? Is it contributing to this issue? I am going to check the ignition wires under the dash tomorrow night. Any help or ideas would be greatly appreciated.

Thanks,

Brian

Hello All -

I modified my new engine harness (changed the resistor wire to a standard 12g wire) and installed the harness. I am still having the same problem (any fan speed except high shuts the engine off and prevents it from starting. With key on and fan at med speed, check with meter or test light at dist, does it have any power? Pull the A/C TCS fuse, does the dist have any power? This will tell us it the dist is somehow wired through blower switch or there is another issue.

http://www.chevelles.com/showroom/data/500/DSC00923.JPG

Will not hooking the yellow wire up to the other solenoid post cause any issues? Is it contributing to this issue?
No. the yellow wire supplies power only when the starter is cranking. Seperate the replaced resistor wire and the yellow wire, check your replaced resistor wire and see if it has power in both the crank and run positions, if it does the yellow wire is not needed. If it only has power in run position, then you need the yellow wire.

I am going to check the ignition wires under the dash tomorrow night. Any help or ideas would be greatly appreciated.

Thanks,

Brian
Check connections at ignition switch.

Ok -

I think I'm finally starting to get my arms around this thing. I think the previous owner had the A/C harness jumpered to the dash harness using the brown tach wire. The A/C harness was connected to a brown wire from the dash harness that had a rubber firewall plug around it. Tracing that back, there was another brown wire spliced in to it going through the firewall to the HEI's tach connection. This brown wire might not be for the tach, but it's definitely part of the ignition system and was definitely meant to go through the firewall given the rubber stopper. I disconnected the A/C harness from this brown wire and taped it off. I took voltage readings at the end of the 12v power wire going to the HEI...full 12 volts at both the start and run ignition switch positions so I don't need the yellow wire. I ran a temporary wire from the ign terminal on the fuse block to the A/C harness power feed. Now the blower works on all speeds with the ingine running or off with the key in the run position. The low and medium blower speeds are now higher than they were and seem normal now instead of being so weak. Now that I no longer have the A/C harness connected to the ignition system and have both the ignition system and the blower working perfectly independednt of each other, I can now connect the A/C harness to the proper dash harness wire. According to my wiring diagram, I need to splice in to a pink wire on the dash harness in order to be connected to the ign wire run beyond the A/C & TCS fuse. I am beat for tonight so I'll tackle that one tomorrow night. If anyone knows the best location to splice in to the proper A/C & TCS fused wire on the dash harness, I would appreciate you letting me know so I don't have to hunt around too much.

Thanks again for everyone's help,

Brian

Ok -

I think I'm finally starting to get my arms around this thing. I think the previous owner had the A/C harness jumpered to the dash harness using the brown tach wire. The A/C harness was connected to a brown wire from the dash harness that had a rubber firewall plug around it. Tracing that back, there was another brown wire spliced in to it going through the firewall to the HEI's tach connection. This brown wire might not be for the tach, but it's definitely part of the ignition system and was definitely meant to go through the firewall given the rubber stopper.
I assume the tach never worked, true?



I can now connect the A/C harness to the proper dash harness wire. According to my wiring diagram, I need to splice in to a pink wire on the dash harness in order to be connected to the ign wire run beyond the A/C & TCS fuse. I am beat for tonight so I'll tackle that one tomorrow night. If anyone knows the best location to splice in to the proper A/C & TCS fused wire on the dash harness, I would appreciate you letting me know so I don't have to hunt around too much.

Thanks again for everyone's help,

Brian
See post first
http://www.chevelles.com/forums/showthread.php?t=54300

http://www.chevelles.com/showroom/data/500/DSC00565.JPG

The Tach did/does work. That's the crazy part. The brown wire that goes out to the tach is spliced in to the wires coming out of the printed circuit. The brown wore that was connected to the A/C harness that had the firewall grommet on it is what probably should have been used for the tach. Is the tach wire supposed to normally have 12 volts on it in the start and run ignition positions? This one does, but the brown wire currently connected to the HEI's tach lead does not. Again, the tach is working. I'm sure I'll be able to get the A/C connected correctly, but I'm now not very confident that the tach is hooked up correctly...even though it's working and seems fairly accurate.

Brian

well...it took about 2 seconds for me to find the brown & black/purple terminal connection from the dash harness to the A/C harness. I connected it to the A/C harness (connections fit like they were made for each other...lol) and everything works now...A/C on all speeds with the engine running. If I remove the A/C & TCS fuse, the blower turns off so I have that hooked up correctly. This connector and two wires weren't on any of my diagrams, and I had previously thought that I had accounted for everything that was part of the dash harness that wasn't connected to anything...but I gess not. I'm still worried about how I have the tach connected and whether or not the brown tach lead should have 12 volts on it or not while the ignition is on.

Thanks,

Brian

FWIW if you remove the factory resistor wire and put in a regular 12 gauge wire you don't need the yellow wire that comes up from the starter. That wires only purpose is to provide a full 12 volts to the ignition while starting the engine.

well...it took about 2 seconds for me to find the brown & black/purple terminal connection from the dash harness to the A/C harness. I connected it to the A/C harness (connections fit like they were made for each other...lol) and everything works now...A/C on all speeds with the engine running. :D:D:D


I'm still worried about how I have the tach connected and whether or not the brown tach lead should have 12 volts on it or not while the ignition is on.

Thanks,

Brian It should not. Tach signal is 12 volt square wave