68 electrical engineering
 

Boy when you look over the electrical system in a 68 GTO it's easy to see where about 3 relays would have made the system so much less likely to burn down.

I was just restoring the console harness and wondered about the big thick purple wires to the neutral switch .. yep, it's feeding a huge load from the battery to the neutral switch, to the ignition switch to the solenoid.

I noticed the purple wires had seen too much heat, I assume someone laying on the starter for two minutes overheated them. A relay on the firewall and they could have removed six feet of voltage sucking wire and a couple of high current connections.

Same with the headlights of course. At least they used one for the blower motor ... but then they also feed all that current through a cheesy speed switch on the dash.

I would have much rather had to replace a relay now and then than have critical circuits sending all that juice through a maze of wiring.

Those GM guys were no dummies as I'm sure you know. Guessing cost factors in as usual, maybe there is some practical, built in safety stuff too?
Every old car that I have owned would for sure benefit from headlight relays.
Interesting topic!

You guys ever try MAD Electrical. Has some pre-packaged stuff like your talking about when separate components may be difficult to source. No Radio Shack anymore.

http://madelectrical.com/index.shtml

Agree! Circuit design was sketchy. But the US wasn't as bad at some of the European cars.

Todays CAN bus is where its at. Even my adventure bike uses it. With a programmer, I can add/delete or tweak functions such as fast or slow modulate the brake light before steady on.....ETC ETC ETC

I'm sure price had everything to do with it. One relay probably cost way more than the wire and a few connectors to run power to a switch and back.

I think my 2011 GMC uses servo motors to operated all the AC flaps, I assume a Pulse Width Modulator circuit in the computer to drive them. So three small wires to any location in the vehicle to operate the flaps and set them in any position you want. Sure there is a headlight relay too .. probably solid state, last for decades.

That Madelectrical has got some decent prices on those OEM style terminals.

Easy to lose sight sometimes how long ago these cars were built.

I just bought a painless harness, I'm wondering if they did away with any of that or just copied the gm stuff.

You once again raise good questions (like bait for me :-ohwell:) and I think you've answered them. Technology has definitely created options and improved efficiency but hasn't changed the basic need to switch and feed power through wires.

With a warranty, there are always both product and repair/replacement costs. My guess is the cost of a relay had to be balanced against the risk for a failure under warranty without it. I have to assume they were highly confident the ignition switch wouldn't fail under warranty or as you found out, they would have made different design decisions! They also had confidence the switch wouldn't fail a year after the warranty expired. Pissed off customers don't come back. So it's not always just the warranty life.. it's more typically the "design life".

Unfortunately for all of us, they did not design the ignition circuit to last 50 years! What's truly amazing and impressive to me is that many still do!



Just to add my predictable old-fart dinosaur ramblings...

FYI - electrical "interconnects" are statistically the biggest cause for failure in any electrical system. Component failures are rare and tend to reflect a bad design, bad understanding of the use, or quality issues when they happen.

Mechanical switch contacts feeding inductive loads are tough to make durable... I bet that ignition switch design was the result of many years of improvement before 1968.

I once worked on a product that needed a lot of field service. Design decisions were heavily focused on that. It's the first time I heard the term "FRU" (Field Replaceable Unit).

I think some of these aftermarket companies are building the best of both worlds. Take a switch that was designed to switch 10-15 amps and have it switching 0.5 amps and the contacts at least will probably never fail ... the mechanicals might but the contacts probably won't

I always forget warranties ... and honestly, most of these cars were probably pretty freakin trouble free for the first 8 years. I know I got my GTO when it was 8 years old, 93,000 miles and everything worked ... only had the usual wear items replaced. I'd say there are many modern cars that don't fair any better.

And of course ... owning a 68 I assume time was frozen from that point forward and any weakness I find was never corrected .. but of course they were. Numerous changes made in the electrical system 68 to 69.

Still, you gotta admit ... some of the decisions were questionable. I'm sure they had their reasons but sometimes it's like if they wired a house they would have put the breaker box in the attic :) And a LOT of issues that could have been solved with wire 1 gauge larger and maybe something other than a 1/4" x 0.030" spade terminal.

I agree it sometimes seems weird without knowing the back story.

For sure the world has changed, though, and not necessarily in a way that makes products more "robust".

For example, do you trust the relay contacts you buy today more than you trust those in your 1968 GM-engineered ignition switch? Which had more engineering behind the materials and design? Which had more cost pressure when developed and marketed? I truly think GM (and other US auto manufacturers) in the 60s and 70s had amazing engineering depth and expertise. In my experience and to your point about cars being more "robust" back then, there were many parts "over-designed" by today's standards.

My old boss used to describe design decisions that cut reliability to save cost "harvesting the margin". One thing technology delivered in the last 50 years are tools to more accurately predict component life. These tools are definitely used to harvest margins. "How good is good enough?" can be answered a LOT better today than in 1968.

I'd definitely trust a modern solid state relay more (Triac, SCRs etc) those things will last for decades unless you pump twice the rated current and voltage through them. Of course that technology was not available back when. I'm surprised most of these aftermarket systems are using mechanical relays, most modern vehicles I'm sure use solid state parts as they must have dozens of "relays".

And look at modern wire connections, environmentally sealed and almost never fail or overheat ... but once again that type of product wasn't available to be sourced 50 years ago.

Probably unfair to compare old to new engineering because so much of it is controlled by the available materials, and the materials have changed tremendously. I'd say it's more often that our old cars electrical systems fail because of material degradation than design issues. Cracked insulation, degraded plastic connectors, lower temperature resistance, lower chemical resistance. In mechanical systems, worse gasket materials, poorer lubricants, no such thing as Finite Element Analysis, less exotic coatings.

I guess some of the more advanced stuff might have been available back then but I'm sure it was prohibitively expensive.

So far my last two GM truck engines have gone 100,000 miles with not a single major part, not a water pump, or alternator or ignition part (not even plugs), actually not even an air filter on either one. One did need a small evap valve. How much of that is better materials, how much is better design?

But then designers and engineers have software tools now that would have been inconceivable 50 years. They can probably simulate years of wear and tear on most component without ever actually making the part. They can model air intake systems for maximum flow, minimum sound and the least carrying capacity for particulates with a desktop computer. Same deal with exhaust systems (and of course now they are SS to comply with EPA requirements for longevity). I bet they can plug in the design for an entire electrical system and stress test it for hot spots and such long before it's ever made.

I guess in the final analysis, if the engineers were giving free reign we probably WOULD have flying cars by now, but companies have to make a profit and old ladies don't want flying cars :)

It was a very popular thing to do to add a relay to help with voltage drop on the purple wire. It was even suggested in a GM tech bulletin. The thing you saw done was to use a Ford solenoid for the relay.
However, even that is a band-aid approach to what is the real problem which is the basic design of the GM starter/solenoid and they way they routed the wires to it without enough heat protection.

This is the best explanation I have come across that explains how a GM starter/solenoid works.

https://autosystempro.com/starter-co...it-components/

Notice that the solenoid has 2 windings in it. One to pull-in the plunger and one to hold it in place once it has been pulled in.

Also notice that the ground for the pull-in winding goes through the windings in the starter. This part of the design is why this starter is so prone to a no-start malfunction caused by heat soak.
This is also why a adding a relay or solenoid is a band-aid at best because you are trying to overcome a high resistance ground problem with lowering the voltage drop on the positive wire. However, it can make the problem better and why it has been done.

The best way to solve the problem the problem today is to go to a mini starter. The solenoid will draw much less current and a relay isn't needed. The size makes it a lot easier to protect the wires from heat too. New wires have much better quality insulation on them than they used 50 years ago too as long as you buy high-quality automotive wires.

So your 1968 GTO is 54 years old.
To illustrate how much engineering has evolved over the last 54 years, take a look at what a 54 year old Pontiac looked like back when your GTO was produced:

https://a4.pbase.com/o4/17/342117/1/...87_Oakland.jpg

This is a 1914 Oakland which was the GM division that became Pontiac.

Thanks, very interesting. A mini-starter is definitely a possibility since I have transitioned away from 100% stock to something I will probably drive frequently. Any system I find glaring problems I'm going to do whatever is necessary to address them.

dataway - My opinion is yes, yes, and yes on all points....

And back to your first post, even if the modern relay contacts fail earlier than the GM switch contacts, you can easily replace the relay.

roger1 - great info and link, thank you! I have to assume the purple wire did not fail often and was protected by a fuse.

It would be fun for me to see the repair history data from these late 60s vehicles. Has this ever been published?

Coming up with a new vehicle design on a 1-year development cycle was an amazing accomplishment for automotive engineering organizations. And they were doing it with slide rules, manual drafting, and typewriters in 1968.

GM was certainly high tech for the time. When repairing a dash tach I was very surprised to see the circuit board was a hybrid "chip and wire" on a ceramic substrate. So I have a lot of respect for the 68 Electrical Engineering!

I put a RobbMc mini starter on my '69.

I'm working on getting it wired up right now. I will be posting details about that and many other wiring upgrades I'm doing in my next build thread post. I am using the American Auto Wire upgrade kit for the car but I'm doing several things under the hood different than they intended with the kit.

The only fuse protection for the purple wire is the main power fusible link that attaches to the starter. I think that is adequate when you consider the purple wire is only hot during engine cranking. If the wire ever failed it would probably be at the starter where high heat over a period of time makes the insulation on the wire brittle and flake off. Same for the red fusible link wire that runs next to the purple wire.

So I'm guessing the signs of heat damage in the console to my donor console harness was someone staying on the starter for an extended period? Probably far beyond the factory recommended cranking time?

It wasn't horrible damage, just the factory female spades melted into the connection for the neutral switch and some shrinking back of the insulation on both switch end and plug end.

I replaced the female spades with tin plated brass double crimps, after trimming back the wire a bit, covered the crimps with shrink tubing, left the females uncovered to help dissipate any heat, so no longer a "connector" on the switch end, just the separate terminals. Just cleaned up the plug end connectors and used anti-corrosion grease.

I'm one of those people that if the engine doesn't start within about five seconds you stop and find the problem. Preferable about one second :)

Hard to know but after 50+ years in NY or anywhere humid, a crimped connector or even a spade lug connection could corrode and have increased resistance. I doubt it takes a long time for high current to heat up a small connector, but melting adjacent plastic could take a while...

Regardless, yours will now be better!

I recently did some research into the solder vs crimp debate ... jeez, and I thought oil threads were bad in the car groups, these electrical guys are very opinionated :)

So I usually crimp AND solder critical connections.

Can hardly wait for this one Roger. Maybe after you post it to your restoration thread, you can duplicate it in the "Electrical Tech" Forum. It sounds like good info in several areas other than the 68-69 Tech Section.

Just thoughts,
Ogre