Restarting My '70 Nova Project

[BravoXray]

I was just getting ready to make a post.

Short answer, no I didn't find what or where the leaking voltage is coming from. I spent a few days with the dash out tracing wires on everything I could imagine was the culprit, but couldn't find it. I even set the cluster up and resting on the steering column, hooked up all the connections that go to it, and it didn't malfunction. I even ran a ground directly to the body, even though there are two other wires that provide hard grounds from the cluster to the body.
Then I finally went ahead in screwed it in place and the problem was back. Unfortunately, there is no room to get behind the cluster and disconnect the harnesses one at a time to try to isolate it. The only possible clue, even if it is related, is that the brake light comes on dimly when the key is in the accessory position, whether the parking brake is set or not. But, pulling the brake fuse makes the light go out, and the leaking voltage problem is still there.
One though I had today was if there is a possibility that the printed circuit that is on the back of the cluster, and carries connections to all the indicators and the gas gauge, might be the problem. So, I pulled the GAUGE fuse, and the problem goes away. Looking at the wiring diagram, there are no obvious points where the leak could occur, but obviously somehow there is. Also, due to the low voltage, that might coincide with the voltage to the gas gauge. Without draining the tank to see if the voltage changes, I might try disconnecting the sending unit at the tank harness to see if that affects the problem. If it does, that would tend to point to the printed circuit, maybe, so I might go ahead and order one and change it just for ***** and giggles. I just don't know.

Was a beautiful day here, so I pulled the Nova out and took it for a 30 mile ride around the area. It runs great, sounds good, and rides pretty good. It is a little noisy inside with the windows down, but I can still turn the radio up and hear it just fine. I even got a couple thumbs up from other drivers, which makes you feel good. In May, the cruise-ins at the Essenhauis start again on Thursdays, so I can make it to some of them this year.
When I got back to the house, I drug out the hose, filled the wash bucket with soapy water, scrubbed off all the dust, and rinsed it off. After drying it of, it looked a lot better.
I also opened the hood and turned the valve off in the heater hose, I forgot to do it before I went for the ride, but it really didn't put out any noticeable heat with the controls set to cold.
And best of all, no leaks!

So, when I decide to pull the dash out, again, I'll post an update.

 

[MossRoad]

Yes, it was a beautiful day!

 

[Alan46]

I was just getting ready to make a post.

Short answer, no I didn't find what or where the leaking voltage is coming from. I spent a few days with the dash out tracing wires on everything I could imagine was the culprit, but couldn't find it. I even set the cluster up and resting on the steering column, hooked up all the connections that go to it, and it didn't malfunction. I even ran a ground directly to the body, even though there are two other wires that provide hard grounds from the cluster to the body.
Then I finally went ahead in screwed it in place and the problem was back. Unfortunately, there is no room to get behind the cluster and disconnect the harnesses one at a time to try to isolate it. The only possible clue, even if it is related, is that the brake light comes on dimly when the key is in the accessory position, whether the parking brake is set or not. But, pulling the brake fuse makes the light go out, and the leaking voltage problem is still there.
One though I had today was if there is a possibility that the printed circuit that is on the back of the cluster, and carries connections to all the indicators and the gas gauge, might be the problem. So, I pulled the GAUGE fuse, and the problem goes away. Looking at the wiring diagram, there are no obvious points where the leak could occur, but obviously somehow there is. Also, due to the low voltage, that might coincide with the voltage to the gas gauge. Without draining the tank to see if the voltage changes, I might try disconnecting the sending unit at the tank harness to see if that affects the problem. If it does, that would tend to point to the printed circuit, maybe, so I might go ahead and order one and change it just for ***** and giggles. I just don't know.

Was a beautiful day here, so I pulled the Nova out and took it for a 30 mile ride around the area. It runs great, sounds good, and rides pretty good. It is a little noisy inside with the windows down, but I can still turn the radio up and hear it just fine. I even got a couple thumbs up from other drivers, which makes you feel good. In May, the cruise-ins at the Essenhauis start again on Thursdays, so I can make it to some of them this year.
When I got back to the house, I drug out the hose, filled the wash bucket with soapy water, scrubbed off all the dust, and rinsed it off. After drying it of, it looked a lot better.
I also opened the hood and turned the valve off in the heater hose, I forgot to do it before I went for the ride, but it really didn't put out any noticeable heat with the controls set to cold.
And best of all, no leaks!

So, when I decide to pull the dash out, again, I'll post an update.

You have more patience than most, my friend!

 

[Fuddyduddy1952]

This: "The only possible clue, even if it is related, is that the brake light comes on dimly when the key is in the accessory position, whether the parking brake is set or not." Is a major clue.
Of course no connection with parking brake and brake light. Is this a parking brake warning light or the brake lights?
If the car is all factory stock and a wiring schematic it would be easy to trace out...but I assume it's not 100% stock. Whatever has been added can cause weird problems.
Last summer I bought this '69 Rambler Rogue.
What sold me was it's originality except for aftermarket stereo which I replaced with a factory radio. Except for ignition, headlights and starter, nothing electrical worked. After 100(?) hours now everything works.
Any gremlin like brake light on dimly I focused on. The light(s) of course is getting voltage somewhere. It's a time consuming pain, but so nice when everything works properly.

 

[BravoXray]

Nice looking Rambler, don't see many of those around any more. I always thought they were a nicely styled car.

The harness is a total replacement harness from American Auto Wire. It is loosely wired similarly to the original, as come circuits have to be basically the same as original to work, but it also has many more circuits and options for retrofit options like EFI.
I am going to remove the dash again, as now the gas gauge isn't working and I want that functioning properly, and I have a new printed circuit for the instrument cluster as I think that may be the culprit.
I also think I might have a method to help trace down the backfeed source, it it works like I think it should, but, I'll have to try it to find out.

 

[the old grind]

I've found grounding to be a big cause of electrical phantoms (including with home/shop wiring) and esp with trailer wiring or with accessories added and no schematic updated or to update.

Dim and/or ghost lights, say when the key is off, is what makes us dig in. Accessories can ground through each other, and yes I've added diodes to grounds* to prevent backfeeding.

Edit: * per accessory vs per bus or attachment to body/chassis.

 

[BravoXray]

Thanks for the suggestion, but I was very meticulous about making sure everything was properly grounded.
The fact that there is a backfeed of ~3 volts into the accessory circuit seems to pretty much rule out a bad ground.

 

[Fuddyduddy1952]

One suggestion is something easy to fabricate. I was (still am?) an electronic repair tech 43 years before retiring years ago and had to think outside the box making "gadgets".
Harbor Freight sells a clip lead set for $2.99. Use that and inexpensive 16, 18 ga. lamp cord. Clips on both ends. Disconnect battery +positive, clip leads one end cable to battery post. Other end to a 12v lamp. Long enough lamp cord you can have that inside car (of course careful it cannot touch ground).
You use incandescent not LED lamp.
Now you have current-limited power. Limited by whatever lamp you choose. If you have a short, bulb burns brightly.
Last week a neighbor called, his trailer lights didn't work. I clipped truck frame ground to trailer framp...lamp lit. "It it supposed to do that?" he asked. Of course not. Truck to trailer had a bad ground.
If you have a parasitic current draw, light will light...current draw indicated by what lamp you use. A #194 is about 1/4A (250mA) while a headlight 3 to 8 amps depending on bulb.
For a short finder sub in a 2 prong flasher. You found short when clicking stops.

 

[Duds13]

Been a few weeks since we had an update. Hopefully Bravo figured out the issue and has been enjoying the car!

 

[BravoXray]

I haven't gotten into it yet. Been busy with a few other projects lately, but I have been putting a few miles on it. The last two Thursdays, when the local cruise-in is held, it's either been raining or threatening rain, so I haven't attended yet.
I'm probably going to pull the dash beck out late this week, or over the weekend. I'll post when I get it out and what I find.
It has been running great though.

 

[BravoXray]

Okay, problem finally figured out and fixed. Fortunately, I guess, it wasn't my wiring error or something I did wrong.
After scanning the circuit diagram for the fuse block and bulkhead connector, I found a dashed line, the only one in all the wiring schematics, that was causing the problem backfeed.
Bear with me, I'll explain it. The accessory wire from the ignition switch goes to the fuse block to power a row of fuses that power accessory circuits. In the instrument cluster, one terminal of the the Generator light is connected to the normal ignition feed which powers the fuel gauge and other indicator lights, Water, Oil and Brake. The other terminal goes into the harness and into the bulkhead connector and then out in the underhood harness to the engine compartment, ending up next to the battery, but is not connected. However, for some reason the tech at American Auto Wire couldn't explain, there is a resistor wire connecting the accessory fuse bus to the generator wire. He couldn't explain why that was done, just that's the way they make them. The stock wire harness has no such connection, so I am at a loss for a reason they would do this, as it provides a direct path, albeit through a piece if resistor wire, between the accessory circuit and the normal ignition circuit. So, whenever the switch is in the accessory position current can feed from through that wire and the filament of the Generator light into the ignition circuit. Because of the resistor wire and the resistance of the Generator bulb, only a small amount of current can pass, just enough, around 2.5 to 3 volts, to make the MSD EFI display try to power up, fail and repeat the sequence every second or two making the screen flash on and off.
Once it figured this out, while the instrument cluster was out, with the ignition switch in the accessory position, on the cluster connector, I could connect the cluster power wire to the Generator light wire with a test light, and duplicate the problem.
To fix it properly, would mean pulling the fuse block out, finding the resistor wire and cutting it out, but, that would be a nightmare working under the dash and having to pull the brake mater cylinder and booster to get access to the nuts holding the fuse block and bulkhead to the firewall. So, instead, I figured out that putting a diode in the circuit between the Generator light and the bulkhead connector would prevent any current bleeding over from the accessory circuit. There is a short harness from the main dash harness to the instrument cluster, so I installed the diode in that harness. I used a 10amp Schottky diode, as they have a lower forward bias voltage, ~.2 volts, versus ~.6 volts on a normal diode. While at this point, the wire isn't being used, if I do ever decide to use it, it will have sufficient current carrying capability and very little voltage drop.
I got the dash completely reassembled this afternoon, and everything works as it should, finally.
Before I had pulled it apart this time, the fuel gauge had stopped working, which I traced to a break in the printed circuit overlay on the back of the cluster, so I replaced that. I bench tested the gauge and all the indicator and backlighting lights, and everything worked. I also checked the circuit going to the level sensor in the gas tank, and since the tank is full, it read about 90 ohms, which is correct. The gauge shows right on the full mark now.
So, after a year of trying to figure out the problem, I finally have it solved and understand what caused it.
That only leaves one problem I have left to resolve. At speeds over 65 mph, I have a driveline vibration. I can feel it in the shifter, and it's speed dependent, not RPM dependent, so it's either the driveshaft out of balance, or a driveline angle problem. Being that the driveshaft is new, I'm thinking it's an incorrect pinion angle causing it. When I was installing the differential and the driveshaft, I must have installed a wrong shim when I set the pinion angle. I'm going to check with my alignment shop to see if I can get it on their alignment rack so I can check the angles while the car is level. I'll update the thread when I get that sorted out.

Everyone stay safe and well.


The dashed line above the fure block and the bulkhead connector is the culprit.

Diode installed in the harness.

New printed circuit overlay.

 

[BleedingOrange]

Awesome, glad you found the issue, and found a way to correct it. Hopefully you get many years of trouble free enjoyment from it. I,m sure the compliments you get from others when you have it out and about have to make you feel very proud of all the effort and hard work you have put into building such a beautiful car.

 

[Duds13]

Amazing work and glad you solved the issue!

 

[BravoXray]

Thanks for the compliments, guys, I appreciate it.

It's nice out today, so I'm going to take it for a drive this afternoon.

 

[BravoXray]

Well, I thought I had everything working when I put the dash back together, and I guess I did, sort of. But, the next time I drove it, I noticed that the left turn indicator and the high beam indicator weren't working. Well fudge! (Not exactly the words I used.)
After a couple more trips, my OCD kicked in and I had to figure out WTF the problem was. Today I pulled the driver's seat out so I could get under the dash to look at the wiring. I was able to get to the connector at the main harness and short connector cable going to the cluster, and power for both those lights was present. More cursing ensued. There is no way to get to the connector that plugs into the cluster to remove it, but using my fiberoptic scope I could see that all the wires were intact and none of the terminals had pulled out of the connector shell.
Now, I did check to make sure all the indicators and the fuel gauge worked before I reinstalled it, since I had replaced the plastic printed circuit and just wanted to make absolutely sure everything was working. However, I used the spare connector from the original harness, not the new one that is used in the car. So, after I disassembled the dash, again, with it on the bench, applying power to the connector failed to power the lights. Hmmmmm. Removed the connector from the cluster and when I touched the copper traces going to the indicators, sometimes they would light and sometimes they wouldn't. Although the copper looked clean, and there were marks that the terminals made on them, there was some coating or something else preventing a good connection. I plugged in the test plug, and all the indicators worked. plugged in the new connector and LT and HB didn't. I took a piece of emery cloth and polished up the traces on the printed circuit, also polished the terminals on the connector, and tweaked the terminals a little to ensure good contact whe installed. Now, everything works again. I wouldn't have believed it unless I saw in for myself, but that was the problem.
So, tomorrow, I'll put it back together, again. Hopefully for the last time. Shouldn't take too long, I have it down to a science now.

 

[Willman]

get this and put a small amount on the connections
Eliminates the “fretting “ on pin and circut board Contacts

 

[BravoXray]

I have a can of Deoxit, I thought about using it, so I will take it to the shop today and give the connectors a spritz before I reinstall them.
Thanks for the suggestion, though.

 

[Willman]

I have a can of Deoxit, I thought about using it, so I will take it to the shop today and give the connectors a spritz before I reinstall them.
Thanks for the suggestion, though.

Regular Deoxit is a cleaner and helps, the Deoxit Gold is a enhancer that improves the connection between contacts, its not cheap though

 

[Fuddyduddy1952]

I used a tool like this a lot as an electronic technician. The chisel end to gently pry connector tabs up a little & wire brush to clean. Over time connector tabs lose tension and become corroded.
Contact cleaner spray is good afterwards.

 

[the old grind]

CRC contact cleaner (2-26?) indoors on electrical stuff. Hoppes #9 bore cleaner on outside stuff to clean and leave a bit of corrosion protection but I often follow it up with a dousing of WD-40 or similar.

btw, & OT but just fired up the skidder after sitting since Covid but w/new starter. 5 gal of hydro didn't get it to the dipstick so it'll get a few filters & likely another 5 or so to get all cyls & the drive working. Still going over elec and hydro circuits daily.

Back to cars & I promise a pic soon of the '80 L-82 Auto C3 than started & ran on 20 year old gas. We started on ityesterday, got the front brakes bled with a new MC and Dave drove it home today ... with flat-spotted tires that shook the car a 40 mph.

<26k mi & I bought it in '81 with 7,400. Gotta be the oldest C3 with headlights that come right up, so hoses and vacuum motors remain intact. Brake, turn, and backups all work. Uh, it was 100% when I quit driving it, and will give it's indoor berth to the skidder. (finally)