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Hey all, new to the site and need some advise. Just picked up a project 74 vette that has the dash and interior out of it. Just hooked up new gas tank and all else looks in place. Would like to fire it up once but not happening.
First question. Is there anything in interior wiring harness that would keep power from getting to engine? Anyone have a basic wiring schematic for engine ignition? Just not sure where to begin. Dont have experience with vettes. Thanks
You could "hot wire" it if you just have to - but I wouldn't recommend it.
All you really need is a wire hooked to your ignition - where depends on if you still have points or what kind of distributor. Then jump the starter solenoid.
I wouldn't do this as you are taking a chance to burn the car down or damage something.
The seat belts are out of the interior also, so I'll have to see what I can do to test that. Seems odd you would have to buckle the belts before starting the car.
I was told by the previous owner that the engine started before they took all of the interior out. Starting to go through the interior wiring to see how to hook things back up. I just figured something is still disconnected. Also noticed I can turn the ignition tumbler without the key in it.
On the 74, there is a wire down beside the brake console that the seat belt plugs into. this stops the car from starting unless the driver is buckled up. I think it is dark tan in color.
Put the seat belt receivers back in the car and insert the buckle into the receiver. it shorts out the jumpers in the receiver which tells the car to start. You don't have to mount them, just set them in.
we don't know if it even cranks, if it has a points ignition, the battery is charged, if other electrics work.. just no information in order to even try to help the op.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi and Welcome!
As mentioned above the 74 Corvettes had to have the seat belts fastened before the car would start. Over time many owners have bypassed the system and there are many ways to do that.
The interlock relay is on the passengers side of the firewall.
To bypass:
Remove the relay and install a jumper wire as shown
With the relay bypassed turn the key to START and see if you have 12 volts at the purple wire on the small inside terminal of the starter solenoid.
This is great info...thanks. I did notice that there is no relay plugged into the interlock bracket in your pic. Thought it seemed odd nothing was plugged in there. I'll try the jumper wire tonight and check for voltage, along with putting seat belt receiver back in.
Seat belt interlock. Buckle up the driver's belt and give it a try.
This! 74 is only year with seat interlock.....car will not start without belts fastened and Your butt in the seat .....there is a sensor where you sit . Same for passenger seat, if a person is sitting in the seat , they have to fasten their belt or car will turn over but won't start.
Most have been bypassed over the years. But one pops up every now and then that still retains the interlock system and sensors.
You really really need a damn wiring diagram , one you can hold in your hand and study along side the car.. ....smh .......
Dude .....go get a nice wiring diagram ...stop banging your head against a wall.
DR Rebuild sells nice LARGE clear easy to read wiring and vacuum diagrams for C3 .
Last edited by LS4 PILOT; Jul 9, 2015 at 11:40 AM.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
The problem might not be the interlock relay.
Originally Posted by Cjf5150
This is great info...thanks. I did notice that there is no relay plugged into the interlock bracket in your pic. Thought it seemed odd nothing was plugged in there. I'll try the jumper wire tonight and check for voltage, along with putting seat belt receiver back in.
If the relay has been removed and you do not see a jumper wire a previous owner may have removed the orange base and connected the lt green/black to the purple and replaced the orange base.
I agree with post 6, we need more information.
Is the battery good?
Are the connections at the battery clean and tight?
Is the battery ground wire under the car and the positive at the starter clean and tight?
Did your car start before you took the dash apart?
Stick or auto?
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Originally Posted by LS4 PILOT
This! 74 is only year with seat interlock.....car will not start without belts fastened and Your butt in the seat .....there is a sensor where you sit . Same for passenger seat, if a person is sitting in the seat , they have to fasten their belt or car will turn over but won't start.
If the stock interlock relay is BAD the engine will not turn over.
we don't know if it even cranks, if it has a points ignition, the battery is charged, if other electrics work.. just no information in order to even try to help the op.
I agree..too easy to jump to conclusions without even the basic of information.
Still not able to figure this out. I put a jumper wire between the purple and green/blk on the interlock switch plug, inserted a seat belt into the drivers buckle. Nothing at all when i turn the ignition. I can get a few dash lights and rear lights if i turn the headlight switch.
It looks like the purple/wht wire from the ignition goes into a two wire connector with the green/blk under the drivers dash. Have no idea where that would plug into, or if its supposed to have a relay type switch.
I would hate to haul this somewhere to have a guy figure it out. Could cost a ton. Any ideas? I took a pic of the two wire connector under dash, and interlock switch. Thete is also another wire connector unplugged nearby and cant figure out where it goes.
Under dash. Looks like the other ends connect to ignition switch and interlock
Near passenger firewall area. No clue where this connects to.
Mine would not turn over as I let the battery die down... Interior lights worked - just nothing when I turned the key - I don't recall the starter clicking.
When I got out the volt meter and tested the battery, it was at 9 volts.
take a picture of the drivers seat belt receiver....and the area above it. there should be a tan connector (if memory serves) that should be coming from the seat belt receiver.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
While your taking pictures take one on the neutral safety switch (at the base of your shifter) and the connectors.
In your first new picture the purple/white and green look like the connector for the NSS.
See if the purple/white has 12 volts with the key in start.
I'll take a pic of the NNS switch, but I have looked at that and no connections broken or missing there that I can tell. I think the purple/wht and green wire connector does run between the ignition, NSS, and back to interlock switch. I just can't see where the connect in the pic would hook up to. It's too short to reach anywhere past the steering column area.
While your taking pictures take one on the neutral safety switch (at the base of your shifter) and the connectors.
In your first new picture the purple/white and green look like the connector for the NSS.
See if the purple/white has 12 volts with the key in start.
Hey, just noticed your in Mt Holly. If your planning to come to Raleigh anytime soon, would love for you to take a look at the car. Could really use some advise!
New 74 Project Won't Start
