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scratching my head on this one

2K views 20 replies 4 participants last post by  Dansk 
#1 ·
My Chevelle has been running great but tonight I went out and started it to see that the dash GEN light was on. Weird I thought because my car has a one wire alternator so I didn't even know that the light was functional. I checked the voltage at the battery and it was charging. 12.4 volts off and 14.3 when running. So I thought well I'll go anyway. Put the car (automatic) in reverse and it dies. Tried it a few times and the same, take it out of park and it dies. So the neutral safety switch must be playing a part. It's odd because the car was fine last time I drove it. Any ideas? I keep saying that I want to rewire the car because I don't know what's been done by others.
 
#2 ·
Check your harness where the reg connector once was. I don't know what method they used to convert the one wire but a picture of that connector or what they did there would send me in the right direction. Check to see if the brown wire is shorting out the in that location. Also see if the brown wire is connected to anything. It's possible to wire the light to function on some one wire alts.

Are there any other wires connected to your alt besides the red charge wire?

Does the alt light go off when you shift out of neutral?

What year is your car?

The only time your neutral safety switch sees power is when you turn the ignition switch to the start position.
 
#4 ·
YOU MIGHT BE IN A DANGEROUS POSITION AT THE MOMENT. SINCE I'M NOT SURE YOUR ELECTRICAL SYSTEM IS PROTECTED PROPERLY, YOU SHOULD BE READY TO DISCONNECT YOUR NEG BATTERY CABLE AT A MOMENTS NOTICE IF YOU SMELL BURNING INSULATION OR EXPECT A SHORT. HAVE A FIRE EXTINGUISHER ON HAND TOO, but disconnect the lead before fighting the fire if one occurs. Be aware that the battery could explode if the short is severe enough. I would probably loosen the clamp so the neg batt cable can be popped off easily if the need arises.

Your ignition circuit may be shorting out causing the engine to die.

I'm not sure what is going on yet, just want you to be forewarned.
 
#5 ·
Thank you, I did disconnect the battery ground based on your advice. My car is a 66. The brown and red wire are just hanging on a connector next to the alternator. They could be plugged in to the excite terminals but aren't. The alternator is internally regulated based on the terminals orientation but they aren't used. There is no voltage regulator up near the horns and no wires there either. My alternator just has the battery wire and also a feed to the an HEI ignition relay from the same terminal. The ignition switch wire picks the relay and full battery voltage goes through the relay to the distributor. I've been scolded before for using a relay but my ignition switch has too much voltage drop for the HEI to run directly. I did replace the resistor wire but still don't get full voltage through the key switch.
 
#6 ·
I use a relay for my HEI, nothing wrong with that. Wiggle the key in the ignition switch and see if the light goes out once the car is running. Also start the engine in neutral and move the shifter to drive and see if the engine stalls. Then turn your idle screw up a bit and try again.
 
#7 ·
Try this, we need to rule out a tuning issue before electrical. or,

You can also pull the HEI power plug and put a test light in the power terminal. Then turn on the ignition and put the shifter through the gears and see if you lose power or the light dims. Either would indicate a short, Return quickly to neutral and turn off the ignition. If you still have power to the HEI you have a tuning issue with the engine.

Sounds like One Wire Bubba got into your electrical system. It's probably a good time to consider a rewire with a reputable harness supplier.

If there is a short, the only time it occurs is with the ignition on and out of neutral. You have tried to go past reverse? Put it in drive ? If you have a Bubbafied electrical system without fuse protection a short in the backup light system could short out the ignition circuit while in reverse.

Unless I'm missing something, that brown wire has to be shorted to ground somewhere to get it to function.
 
#8 ·
I did quite a bit of probing after work today. It seems that I'm over due for a new harness. This particular issue is that there is 12.4 volts to the key switch but only three volts from there out to the fuse block. In probing around though I'm seeing low voltage in a lot of places down around 11 volts. It's obvious that someone re-wired under the hood but under the dash is original and somewhat butchered. I plan to go to American Autowire for a stock harness. I think they make a factory fit to work with HEI and a 12SI alternator. I'll also source a new GM ignition switch. Anything else that should be replaced after 53 years?
 
#9 ·
Did you see in the stickies that there were wiring diagrams for your year? If you click on them you can download them without the watermark.

Head light switches seem to develop issues over the years so if you want to throw some cash around it may reduce problems in the future.

Your ignition switch might be bad. But the voltage drop may be caused from the short in the wiring somewhere. Disconnect the 2 brown wires( one solid brown and one brown with a white trace)) and see if your ignition voltages return to near batt voltage. The 2 brown wires lead out to the bulkhead connector where they join and continue out as a solid brown wire to the regulator. One is a resistance wire and the other leads to the gen bulb and then the bulkhead connector. If it's not hooked up to the reg or alt in someway, then there should be no continuity to ground or power on those wires at the switch when disconnected.
 
#10 ·
I think you are on to something. The brown wire runs out to my alternator but is not connected.(see photo) I checked and it is not shorted to gnd. in the engine compartment but when I reconnect the bulkhead it is 8.6 ohms to gnd so there is something going on under the dash. Can you pull the ignition switch without pulling the whole dash? It looks like it will be hard to access.
 

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#11 ·
For the 66 gnition switcg you remove the tumbler from the switch first. Watch the video. Then unscrew the bezel and push the switch in. If you need pliers to get a grip. cover the jaws with elect tape so you don't damage the bezel. Disconnect the batt neg cable so nothing shorts out. You can hook it back up when it's clear of the dash for resting.

On your car the release holes should be on the right side of the key hole. The top hole will release the tumbler.



 
#12 ·
Looks like it was set up for a 12SI before the one wire alt was installed. Without anything connected to that connector at the alt you should never get an alt warning light lit. So that's where I would look. The brown or brown wire with the tracer are shorting out somewhere. Disconnecting and taping off the connectors at both ends might isolate the short. But I would feel better to know that the short or issue has been located. No telling the extent of the issue or possible damage that can occur until you find the issue.
The warning light gets power from the ignition switch which is grounded at the alt when a no charge condition exists. As soon as the alt begins to charge the ground is interrupted and the light goes out.

If you get the switch out and disconnect the 2 brown wires and then see batt volts in the rest of your ign circuits you have found the culprit. Check your switch out puts to rule out faulty switch contacts or resistance in the switch.
 
#14 ·
I took the ignition switch out and removed the brown wires. 12.1 volts to the ignition now so yes, the browns are the culprit. I then disconnected my battery and read ohms from the brown wire terminal that I removed from the ignition switch to gnd., it was 16 ohms. Tracing the schematic I see that the solid brown goes up to the fuse panel and feeds another solid brown that goes to the turn signal flasher. I removed the flasher and no change. I then followed the brown w/white trace wire. It goes up to the bulkhead connector. I disconnected the bulkhead and only a small change resulted. Remember that my brown wire under the hood goes nowhere so it shouldn't have had any affect. That same wire with the white trace also connects to a brown wire that feeds the generator indicator lamp. I removed that bulb and the resistance to gnd actually went down from 16 ohms to 8 ohms.
My next step was to check the fuse block. There was a wire attached to "Fused Accy" that powers my tach and transmission temperature gauge. I disconnected that wire and no change. Am I missing anything?
 
#15 ·
have a funeral to go to so can't dig in now, hopefully someone can see the issue. I'll dig back in when I get back

Your resistance will change when you remove the bulb because it actually acts as the resistor in the wire. I could be wrong, but I think somewhere some how your brown wires are shorting to ground somewhere.
 
#16 ·
The one brown wire runs from the indicator light to the bulkhead connector and to the VR.

At inboard bulkhead connector there is a spliced additional wire that runs to the ignition switch and then another spliced wire to/through the fuse block then to the heater sw. I believe this is the lamp test wire that will cause the alt light to illuminate when the key is on and the engine is off. If you pull the fuse the ohm's reading should go away.
 
#17 ·
I pulled the fuse marked heater and the reading did not change. I also noticed that it was 16 ohms earlier and is now 21. By accident I hit the directional lever and the reading did change a little when the blinker was on. All of this done with battery disconnected.
 
#19 ·
I put everything back together, the light is out and it is acting normal again. It bothers me because I didn't find or fix anything. I'm thinking that the 16 ohms is normal resistance through the bulb and other parts of the circuit. I think I disrupted whatever was shorted in the first place. I bet it comes back but I don't know what it is.
 
#20 ·
My old 67 ignition switch acts funky occasionally and I have to turn the key towards the start position and let it return sometimes because my voltmeter will be at 12v charging vs the 13/14 that it normally charges at. Which is why I suggested wiggling the switch earlier. Its been doing this for 10 years.
 
#21 ·
I ordered a new switch, I can tell that mine is tired. A huge thanks to both Al and Eric for guiding me through this. I didn't pin it down but i learned enough that I can now go after the problem if it rears it's head again. I still plan to replace the entire wire harness this winter. I need that peace of mind and can fix the heater and radio at the same time when the dash is out.
 
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