Ok guys, I am hoping you can help me out on this one. Have been trying for a couple of days to run this one down. Recently replaced some parts, Headers, new under drive pulleys, alternator, alt bracket, water outlet, and new hose. Had been driving it some previously and had an issue once before where it acted like it did not want to start. So it is leading me to believe that it might be the clutch safety switch. Not sure. When I turn the ignition key I get nothing.

Here is what I have done:
1. Checked battery, all good connections, have power-lights and horn working
2. Checked battery cables, ground wire to frame is good
3. Re-installed old alternator to rule out bad connections or bad alternator
4. Jumped starter on two terminals had power
5. Took off the starter and had it tested, tested good, re-installed
6. Located the clutch safety switch and jumped the two purple wires on the connector, nothing
7. Have new MSD coil, so should be fine there
8. Down to testing the ignition switch I guess

What I need to know is how do I go about testing the ignition circuit for power. I am going out to get a circuit tester. Any ideas?

 

Is the purple wire on the S terminal (engine side) of the starter solenoid? Check it for 12 volts when the key is turned to "start". If you don't get 12volts, then you know places where to start looking. Ingition switch, adjustment, wiring, etc.

There is a ground wire that lots of people accidentally put on the big solenoid 12v. I don't think that keeps it from starting though, just keeps the wipers from working right.

 

All true.
Make yourself a 12v test light with a brake light bulb and some alligator clips. clip it on the purple wire on the S terminal and ground and hit the key, The light should come bright every time.
If it does not, then start working backwards through the start circuit. If it does, but still no start you have a starter problem, keep looking. Be sure the engine ground under the right side motor mount is good, it mave gotten cooked by the new headers

 

Yes, the purple wire is on the engine side terminal. I was very careful to re connect everything back the same way. I don't have a volt meter yet, but I am thinking that my clutch safety switch might be the culprit. Does t have an adjustment to it?

 

Thanks guys, Actually the engine ground cable connections are good and clean but the cable itself has seen it's better days. I am going to try and make a 12v tester right away and check it.

 

...here's another little test to do. Turn your headlights and have someone try to start the car by turning the key. If your headlights go "dim" or loose their brightness, voltage is trying to turn the starter and it may either be "bound up" or have a "flat spot" in it. If the headlights DO NOT dim, voltage isn't going to the starter(at least not enough cranking voltage).

...1974s and early '75 Corvettes had a seatbelt/by-pass/interlock module relay up on the passenger side firewall above the heater core cover and has an orange plastic base with a silver cadmium relay cover with a black rubber/plastic by-pass button. This went bad on my '74 about 4yrs ago and took me more than a few hours to also figure out why my starter wouldn't crank my '74. I had to by-pass it internally under that relay cover that comes off by gently prying and opening up a few bendable tabs. Been perfect ever since.

 

You can take the seat belt interlock out of the system by opening the connections under each seat.

 

Ok, made the test light and tested the starter. Attached clip to s terminal, ground and turn key. NO light. Tested headlight brightness. Very bright, turn key same condition. I do not think the starter is bound as I had it tested off the car and it spun and tested as passed. I guess I need to start working backwards as suggested but not sure where to go next. Never heard of the seat belt interlock. Do I just un-clip the connections.

Also tried to see if I had power to the coil. Attached to power side and grounded and light came on, but when I attached to both terminals no light. Hmmm

Where do I go next? How do I test the ignition switch or what would be next in line?

 

I looked at the wiring diagram for my 75 and it says the purple solenoid wire goes to the seat belt interlock relay, the starter wire from the ignition switch side is light green/black going into the seat belt interlock relay. I'd check those wires for 12 volts while trying to crank the engine. There is a reset button on my seat belt interlock relay, might try pushing that too.

The seat belt interlock relay is on the engine side firewall, passenger side

 

How to bypass the seatbelt interlock override relay if it has gone bad (not my webpage):
http://home.comcast.net/~vettfixr/page16.htm

Nick

 

...I did not have power from my ignition switch to my starter until I did the exact same by-pass fix using vettfixr's method.

...if your override relay is bad, this "repair" will by-pass it correctly.

 

One thing that I've gotten in the habit of checking on these older cars is the ignition switch when all of the obvious things check okay.


This switch is clamped together and over time the clamp (actually little metal fingers) can let loose. If the switch isn't held tightly together it will act up intermittently by not allowing power to flow to the starter solenoid.

You can try reaching down to the switch (on top of the column near your feet) and squeezing the switch to compress it as you turn the key. If it appears loose, or you get an intermittent electrical response as you do this, the switch needs to be replaced or worked on.

Also try moving the ignition rod that goes between the key switch (at the top of the column) and the ignition switch along the top of the column. The ignition switch is held onto the column with some small sheet metal screws that can work loose. If they work loose, it will allow the entire ignition switch to move instead of the internal contacts of the switch which can again result in intermittent continuity problems.

Good luck... GUSTO

 

Gentleman, Thanks for your valuable experience and help! It was the seat-belt interlock relay bypass gone bad at the firewall. I jumped the terminals as described in the article and vola...HOUSTON We Have IGNITION.

Thanks again to all for their suggestions and comments. Great Forum!!

 

Do you know if this will work for a 1977?

thanks

 

77 does not have seatbelt interlock. This was a one-year-only mistake for the American auto manufacturers.

 

I would agree with this being a one year mistake as far as I know. Try running thru my list of trouble shooting and the other items mentioned to find your problem. Give us a little more info on what you have going on.

Good Luck

 

the seat belt starter relay interlock switch was the problem with my 74 by passed it with a wire.. part# is 1243384 very hard to find but is available on ebay for about $150

 

. If someone pays $150 for this part, they are an idiot. Bypass it and be done with it!! Mine works perfectly!

 

If all that dosen't work, the drive gear inside the steering column driven by the ignition key cylinder has been known to fail too. If you can pull the ignition switch off the top of the steering column and sucessfully start the car without problems start looking for an inner gear failure. Don't ask me how I know this, it was many hours of frustration before I came to the proper conclusion and found the real culprit

 

There's no need to butcher a pricey good looking relay (working or not)
It's much simpler to just splice the green and purple start wires behind the orange mount and leave the relay intact.