I haven't been able to get my '74 convertible to start since March. The last time I tried to start it the starter turned over, but the engine wouldn't catch. I figured that my (refurbished) Q-Jet was finally shot, so I took the time to swap a new carb in and run a new hard line. I changed my plugs, plug wires, oil sender, and re-sealed my distributor and headers while I was at it.

While I did that I cleaned up some oil where I had a valve cover leak, and took the starter motor off to clean it up. I have what I think is the original Delco Remy unit. Cleaned it up, got it back on, and turned the key in the ignition hoping my new fuel line didn't spray gas everywhere.

Nothing. No click, whir, anything. I have lights, buzzer, etc. I took the starter off and hauled it and the battery to Autozone for testing. Both turned out to be okay. Re-attached it, no change. Replaced my ground strap since it was in pretty bad shape, nothing.

I've been using the micrometer to get an idea of what is going on, but I haven't solved it yet. I've gone through most of the Service Manual following the No Crank steps. When I use the micrometer on the B terminal I get 12 v with ignition in ON or START. I also get 12 v at the R terminal with ON and START. The S terminal gets nothing.

I back tracked the wires, my S wire at the ring terminal is red, but about a foot further back two purples are joined. The R wire heads back toward the ignition coil, and B wire is okay. I tried swapping my wires in the midst of testing thinking I'd mixed them up. No joy.

I next tried prying out my shift console and used the micrometer on my neutral safety switch. On the bottom purple wire it gets 12 V all the time, the top purple wire only gets 12 V in Park or Neutral. I'm guessing that means it's good. Oh well, I've wanted to replace the parking break boot and my rear compartment trim frame.

Before tearing into the ignition, I thought I'd follow the starter interlock relay tree. I unplugged the connector by the fuse block that has the green, yellow, and orange wires. That didn't help. I don't have the bypass block on my relay, PO must have ditched it.

What's weird to me is that the R wire is hot even off the terminal and the S gets nothing either way. That's why before I looked at the wire colors I switched them. After I made the swap, I only got 1.5 v at the S terminal off the R wire that was 12 v off the post.

I'm at a loss, sorry for the wordy read. Last stop steering column?

 

The wire to the r terminal will have voltage with the key on because the other end goes to the coil. Does your 74 have the starter interlock relay on the firewall? There should be a reset or bypass button on it.

 

A PO removed the interlock bypass logic block so the blade type connectors are open. One of the prongs, my apologies for not having a picture, gets 12 v. I haven't previously needed to buckle up to start. I thought the R wire only got power from a contact finger in the solenoid attached to the B terminal, hence my confusion.

Thanks for the reply.

 

What about the fusible link?

 

The only fusible link I can identify is on the wire for the B terminal. It doesn't look crispy, and I have lights. Is there another fusible link that I'm missing somewhere?

I sat down and re-read the service manual. With that said I think there has to break in the circuit between the solenoid terminal and the neutral safety switch. As I described it in my initial post, the neutral safety switch only lets 12v through in park or neutral. Maybe I pulled a wire loose at the interlock block while working.

I think I'm going to grab the multimeter, and follow the purple wires as far as I can from the solenoid back. Now to enlist my wife to crank the car while I test. I didn't realize that the S wire would only be hot when the ignition was turned to Start, but now it makes sense. Wish me luck, I'll update if I figure this out or get stuck again.

 

Some observations:

1. I undid all of the wire tape up to the firewall and there aren't any visible breaks or blown fusible links.

2. I found that when my wife sat in the driver's seat the neutral safety switch didn't get 12v. When I sat in the seat it did, and the switch seemed to operate normally.

3. The pink wire at the interlock bypass block gets 12v.

I'm thinking of buying a bypass relay for more testing. I feel like every time I look at the wiring diagram I understand it a little more.

 

This relay on the firewall is interrupting the start (S) wire.
It's problematic and no longer available.
Easiest to just solder the green and purple wires together.
I also just unplug the seat sensors under the seats, but not necessary if the relay is is bypassed.

 

Here's under JC74's hood.
Looks like someone already did the bypass.

 

?
With the key in start you send power from the ignition switch to the NSS.
The NSS must be in P or N to send power to the starter.
Here's a basic schematic:



See if you have 12 volts to and through the NSS.

 

Noonie,

What does the green/black actually do? When I test it for continuity with the multimeter I don't get a reading (ignition in RUN or START).

As you probably know, the pink wire being hot with 12v, I jumped the pink wire to the purple wire and the starter solenoid engaged. Also jumped the B terminal to the purple wire plug on bypass relay block (attached to firewall) with the same result.

Pete,

I've had that pic on my phone for a few weeks. The NSS checks out with the multimeter for continuity. When I shift through the gears the circuit breaks. We've always said that the car hates my wife. I think it was my own lack of experience with the multimeter giving us a bad reading while she cranked it.

Some better pictures below. You can see where my two purple wires come together. I didn't change anything with the starter wiring when I started "refreshing" the top side of the engine, so I'm stumped as to why this is happening.

 

At the ign switch on the column, you will see a purple/white heavy wire, from there to the neutral switch (changes to green), then to the old firewall relay and then to the S on the solenoid/starter (purple).

In start position it should test 12vdc all the way, the other wires are meaningless, if the firewall relay has been bypassed. Only wires to be concerned with are the 12ga purple/white, light green/black and purple.

 

Well, with the way you described that, it sounds like a bad thing that the green/black wire doesn't have power. The purple wire on the relay block just joins with the other purple wire coming from the firewall further down by the starter. That means that there has to be a break from the neutral safety switch to the relay block, right?

Does the interlock block (I think that's what it is, says Delco Remy on it) under the radio ever go bad?

From the neutral safety switch the are two purple wires. Bottom is solid, top is purple and white. The purple and white wire only gets 12v in Park and Neutral. These two wires go to a connector just in front of the radio and like you said, they change to purple and white and green and black. From there it goes into a bundle of wires that run under the radio, left to the driver's side, and then up in the dash to where I can't follow.

However, there is a green and black wire and a purple and white wire running from that Delco Remy box into the same bundle that has the connector from the neutral safety switch. I think a dark green and a pink attaches to the box as well.

I got excited when I found an L shaped connector with a green/black wire and a purple/white wire hanging out unplugged near my fuse box, but realized that it must be the connector for the manual neutral safety switch and should attach to a clutch (I have a TH400).

 

@ Noonie,

I figured wth, I'd use the test jumps I bought at Radioshack and connect the green/black and purple/white at the relay block. Had my wife crank it and viola, starter fired up.

It still pisses me off that I can't figure out what changed for me to have to jump that wire.

 

Maybe somebody jumpered it and it just fell out.

 

Sounds like you disabled the relay under the radio when you played with the smaller ga wires on the firewall. As you mentioned, the original ground strap was probably your problem before you got into the wiring. As I mentioned earlier, with the original system, just disconnect the seat plugs and jumper the interrupt at the firewall.

Now you have a straight shot like earlier cars.

 

Thanks for the assistance! I see plenty of '74 electrical threads on this board, so I don't feel like I'm being singled out.

 

You dove right in to an electrical problem and fixed it for FREE.
Pat yourself on the back!

To little to late:
Here's a schematic.

 

Just got wind they shipped my Q-jet today. Q-jet power.com I am a firm believer in these carbs. The one I have on now is for a 396 with A.I.R. Someone swapped out the original. But am getting back a rebuilt numbers correct. Will make a big difference

 

You've been waiting for a long time-- this thread is from 2013..