I have a 67 sb. The other day I installed a new Dewitts Radiator. Upon completion I took the car for a test ride. I drove around the corner (1/8 mile) and the car just shut off. I tried to restart but there was no power. I got out and checked battery cables which were tight and free of corrosion. I got back in and the car cranked right up.

I drove it down the road about a mile and when turning onto a side road, the car shut off again. I wiggled the cables and after a few tries power came back and I drove it home. I left the car running while wiggling all the electrical wires I could find and could not get it to shut off. I checked battery cables for any place that was bare and maybe ground out but they look good. With the car running I removed the positive lead to make sure the alternator would keep the car going... no problem there.

I noticed tat when the clutch was pressed, it would move the wiring harness that comes down from the steering column. to be safe I tied the harness back. I drove the car for over an hour and can no get it to shut down.

Does anyone have any ideas of what could cause this? or what else I can check? I did replace the ignition switch about two years ago.

 

Check your harness plugs on firewall....under the Master Cylinder....

 

You found the problem...I read about this frequently on the forum.

The main harness plug is of a rather lousy design and is the culprit...it works loose and the car shuts off completely. Others have figured out a work around to avoid the intermittent issue but I can't speak intelligently to this fix.

I replaced the under hood wiring harness and managed to break the retaining clip on the main harness plug to the firewall. I used wire ties to help keep the plug in place but I am sure I will have the same problem at some point.

Gotta love 40yr old technology...

Cheers,

Frank

 

The engine harness was replaced years ago. I did check the connectors that go onto the firewall and they seemed tight. During both of the shutoffs, the only wires I touched were the battery cables.
Once I got it home is when I checked all other wires.
I reached under the dash and tried moving the ignition switch wires but still could not get it to shut down.

 

The wire that kills the power to the interior and ignition is the red wire in the right hand bulkhead connector beneath the master cylinder. It's the closest connector to the center line of the car and it's larger than the other wires. The pins inside the connector can get corroded or bent so they make intermittent contact. You need to clean and tighten the red wire pins, or bypass them completely.

 

Check the wire from coil to inside of disturber cap ,pull cap make sure its tight inside and on small nut on coil, it happened to me a while back

 

I will check the red wire and be sure that it is getting good contact. I installed a HEI ignition years back to eliminate the coil/points issues.

 

I had my 67 stall at the same traffic light 3 times . It died the bie medal contacts inside the worn ignition key switch would wiggle back losing contact .When I dropped the ignition to check it started up.
Gravity caused this problem ,New ignition switch fixed.

 

Rare option, those ingestion switches with bie medal contacts.

 

Gotta love these " complete the word " helpers on these computers!

 

I think it makes them feel better that they got to fix something

 

He didn't get your meaning. Just an idea, when you type something that's going on an international forum, read it before you submit, then you can correct the computer correction.

 

I will try to check the connector on the back of the ignition switch to see if shows any sign of being loose. I will also find where the red wire comes into the fuse box. That would allow me to check for voltage there if the car shuts off again. If I get voltage, then I would guess that the problem would be in the ignition switch.

 

According to the schematic.. it looks like the battery power first goes to the horn relay then to the fuse box. I now wish I could get it to shut off again so I could isolate where the power is being lost.

 

I can't make you believe me, but I told you where it's being lost.

 

In addition to the common problem with the main bulkhead connector, which you may have actually fixed with the "wiggle" check, is another hot spot. It's what feeds that bulkhead.....It's the buss bar at the horn relay as you've found.

If you were working around the radiator, there at the horn relay there is a black wire with a terminal at the buss bar. The black wire is a high temperature insulation covered 16G fusible link. The other end is a spade terminal rubber covered plug which connects to it's mating rubber plug terminal to the 12G Red wire in the forward harness which feeds the entire car through that bulkhead connector.

I'd recommend that you check that buss bar area for corrosion or loose connections in the link terminals since you were around it working on the rad. A few weeks ago someone forced a dead short under their dash Brown ACC wire plug to Cluster ground and blew that fusible link. The entire car shut down, except the horns, as those are fed from the buss bar directly. if it was pre '67, it would have fried his harness.

There isn't a good pictorial of this wiring in the '67 AIM, I believe because the forward harness and Horn Rely arrived as an assembly with the wires and fusible link already connected.

Also below. The original wiring diagrams of the buss bar connections were wrong, showing a visual/phisical connection of the 12v feed directly to ground. This causing some innocent pre-'67 re-wirers in the past to burn up their harnesses.

Rich

 

Thank You.
I've been working on a charging problem for a few days now and while looking at the 67 AIM, I could not fathom why the output of the alternator went directly to ground on the horn relay. The AIM manuals should come with a list of corrections/changes.

 

Way to go Rich now that's the way to explain the problem others can share and benefit very well done

 

Glad it's helped clarify some confusion. A few years ago someone here on CF inadvertently followed the Wiring Diagram regarding the ground at the Horn Relay. He tied the Black Ground to the Buss Bar at the horn relay just like the diagram showed, connected the battery, and fried the harness. The Black ground connects at the mount bolt for the relay to the radiator support. I don't recall what year, but it was pre-1967, when there were NO fusible links or Fuse protection on any Corvettes at the main source in their wiring.

Thanks. It's too bad there are so many wiring diagrams out there that are wrong. It's really unfortunate that the electrical system designers didn't catch that error when it went out for review.

Rich