ENGINE HARNESS

TECH NOTES:

WHAT IS THE SEATBELT / STARTER INTERLOCK SYSTEM?
This system prevents a vehicle from starting unless the seat belts are fastened. But it goes beyond that. The seat belts must be fastened within a specific sequence. For example, the driver (and front seat passenger) must get into the car, close the door(s), sit down, and then fasten the seat belts. If the seat belts are not fastened, or if they are fastened in an incorrect order, the car will not start.

WHAT VEHICLES INCORPORATED THIS SYSTEM?
All 1974, and early-to-mid 1975 vehicles had the seat belt interlock system.

HOW DO I IDENTIFY IF MY VEHICLE HAS/HAD THIS SYSTEM?
All 1974 vehicles had the seat belt/starter interlock system. As for 1975 vehicles, unless you are the original owner or know the history of the vehicle, unknowing wiring modifications by previous owners or repair shops can make this identification difficult. We suggest trying to locate the specific components of the interlock system within the vehicle.

- Logic Module and Sensors often located behind or under the seats. (in Corvettes, it's located behind the seats)

- Starter Interlock Relay mounted in console or under the dash. (in Corvettes, it's mounted in the console)

- Manual Starter Bypass mounted on firewall or on the fender well. (in Corvettes, it's mounted on the firewall)

- According to an early 1975 Technical Service Bulletin (TSB) issued by Chevrolet (and probably pertaining to all GM passenger cars) "A new non-sequential 4 to 8 second delay seat belt system will be installed on all 1975 Chevrolet passenger cars built after February 24, 1975. The new system will have an instrument panel warning light that will illuminate every time the ignition switch is turned on whether or not the driver's seat belt is buckled, but will automatically go off after 4-8 seconds. The buzzer will also be controlled by a 4-8 second timer, but will operate only if the driver has not buckled up prior to turning on the ignition. If no attempt is made to buckle up after turning on the ignition, the buzzer will also shut off after 4-8 seconds."

WHAT DOES THIS ALL MEAN?
According to the TSB information above, Chevrolet is stating that no cars built after February 24, 1975 had the seat belt interlock system. However, we recommend that you verify all of the information provided above.

CAN I BYPASS OR DISABLE THIS SYSTEM?
From our experience, there is no documentation published on how to do so (most likely due to liability reasons). We can not offer any assistance in this area.

CAN I REPAIR THIS SYSTEM?
Repair of the seat belt interlock components is limited to their replacement. Testing the system requires the use of a special tester, which connects to the seat belt/starter interlock system at several points. About the only place that you are likely to find this tester, if you're lucky, is at your local dealer.

CAN I ELIMINATE THIS SYSTEM?
If you have a 1975 GM model vehicle, it is possible. However, because the interlock system was integrated into several wiring harnesses, you will usually need to replace the Dash, Engine and Rear Body Harnesses with harnesses made for "WITHOUT seat belt interlock system".

NOTE: If you've made the decision to completely rewire your 1975 vehicle, we strongly recommend that you purchase your wiring configured for "WITHOUT seat belt interlock system". Doing so will allow you to eliminate all of the electrical components that are part of the seat belt / starter interlock system; components that may eventually fail, are no longer made, and are hard to find.

CAN I FIND REPLACEMENT PARTS FOR THE INTERLOCK SYSTEM?
We offer some wiring harnesses for 1975 GM vehicles with or without the interlock system. However, the other components of the system (logic module, sensors, bypass device, and relays) have long been discontinued and are difficult to find. We do not know where to obtain these components but suggest a junk yard, swap meet, eBay, or a car club member.