Hi gang,
My 1974 2.0L seatbelt interlock is suspect.
The car is new to me (33K original miles). The car was a 1.8 and a new 2.0 engine installed (3K miles ago) with duel weber 40s installed). The wiring and engine bay was cleaned up. The car always cranked (since it was delivered) but did not start. Since then I got it going/fixed by:
Changing the points (changed to pertronix ignightor II because the car carrier guy left the key on and melted my points and T12-5 wire which is the wire to the coil melted and I replaced).
Replaced the fuel pump (didn't work, located in the steering access area, cleaned/buzzed out the relay board, checked wiring etc..)
After replacement, he fuel pump buzzed (first time) but the starter did not engage (first time that happened).
I knew your book pretty well and I jumped pin 50 and C (on the SBIR) and the car started !! (Recently failed seatbelt interlock relay because I replaced the fuel pump??)
My questions now are:
1. Should I leave the SB Interlock relay(SBIR) in?
2. The seatbelt light never worked .. haven't check the bulb or CCA yet, could it be related to the SB Interlock relay(SBIR)?
3. E-brake light never worked.. have checked the bulb and have continunity to BRN/YEL wire to pin A (SBIR), could it be related to the SB Interlock relay?
4. Oil Pressure light never worked.. haven't check the bulb yet, could it be related to the SB Interlock relay or because I have a guage?
5. Defrost light on console never worked..haven't check the bulb (looks ok) or wires yet, could it be related to the SB Interlock relay?
I will check the bulbs and wiring soon, just wanted to get your opinion if this could be related to the SBIR.
Also the buzzer next to the SBIR works on the passenger side (i.e. buzzes when the passenger door is open and the key is on) but not the driveres side door (but the interior light works fine with both doors). The seat sensor has been connected and disconnected with no difference.
Do you have schematics of the SBIR and/or the 74 style buzzer (not in Haynes). I would rather replace a "suspect" relay (but rather not pay $52 to guess) before I pull things apart .
Thanks,
Tim
Full Version: Seatbelt Interlock Question for Dr 914
You got a lot of things going on here...I always remove the Seat Belt Relay and connect the two large (#10 size, I think) yellow wires together...forget the Relay forever...Of course then it's not "as original", but I prefer reliability...
E-Brake, Oil Press, and Defrost Lite have nothing to do with each other or the Seat Belt Relay...
E-Brake lite, check the bulb first, but the lite bulb has power directly to one side...The switching mechanism is on the ground side with the switch below the E-Brake handle...Pull it out and see if it works...It gets filled up with rust and crap over the years and does not work...If it's OK, trace the Haynes manual diagram and you will find it is joined with the wire from the master cylinder up behind the multi-gauge...Got to have a bad connection, broken wire, etc...Pretty simple to trace...
Oil Pressure lite should still work, even if you have the console...Check the wiring diagram in the Haynes...As I remember, the G wire on the sender goes to the relay board on the 12 pin connector, thru the board to the 14 pin connector and to the gauge and up to the lite...But the console may have been added later and some people run two wires (G pole and WK pole) directly from the sender to the gauge and hopefully the green with black stripe on to the lite...But the PO may have deleted the lite when they installed the console...If you have pressure on the gauge, I would start under the console flat board right by the base of the shifter...
Defrost Lite is just a bulb hot wired on one side and comes from the headlite switch...The ground side is the screw to the body which hold lite assembly to the floor...Remove the bottom board around the shifter (you gotta remove it anyway to solve the above problem)...The hot wire to the Defrost lite is blk/blu...Maybe when they put the console in, they did not use a long enough screw to make good contact to the ground side of the assembly from the body...But check the bulb first...
Whew !!!...Didn't know I knew that many words...
2-OH!
E-Brake, Oil Press, and Defrost Lite have nothing to do with each other or the Seat Belt Relay...
E-Brake lite, check the bulb first, but the lite bulb has power directly to one side...The switching mechanism is on the ground side with the switch below the E-Brake handle...Pull it out and see if it works...It gets filled up with rust and crap over the years and does not work...If it's OK, trace the Haynes manual diagram and you will find it is joined with the wire from the master cylinder up behind the multi-gauge...Got to have a bad connection, broken wire, etc...Pretty simple to trace...
Oil Pressure lite should still work, even if you have the console...Check the wiring diagram in the Haynes...As I remember, the G wire on the sender goes to the relay board on the 12 pin connector, thru the board to the 14 pin connector and to the gauge and up to the lite...But the console may have been added later and some people run two wires (G pole and WK pole) directly from the sender to the gauge and hopefully the green with black stripe on to the lite...But the PO may have deleted the lite when they installed the console...If you have pressure on the gauge, I would start under the console flat board right by the base of the shifter...
Defrost Lite is just a bulb hot wired on one side and comes from the headlite switch...The ground side is the screw to the body which hold lite assembly to the floor...Remove the bottom board around the shifter (you gotta remove it anyway to solve the above problem)...The hot wire to the Defrost lite is blk/blu...Maybe when they put the console in, they did not use a long enough screw to make good contact to the ground side of the assembly from the body...But check the bulb first...
Whew !!!...Didn't know I knew that many words...
2-OH!
Could be a couple of problems, just wondering if the SB relay could be related.........
QUOTE(pin31 @ Jan 31 2007, 03:47 PM) 
Hi gang,
My 1974 2.0L seatbelt interlock is suspect.
The car is new to me (33K original miles). The car was a 1.8 and a new 2.0 engine installed (3K miles ago) with duel weber 40s installed). The wiring and engine bay was cleaned up. The car always cranked (since it was delivered) but did not start. Since then I got it going/fixed by:
Changing the points (changed to pertronix ignightor II because the car carrier guy left the key on and melted my points and T12-5 wire which is the wire to the coil melted and I replaced).
Replaced the fuel pump (didn't work, located in the steering access area, cleaned/buzzed out the relay board, checked wiring etc..)
After replacement, he fuel pump buzzed (first time) but the starter did not engage (first time that happened).
I knew your book pretty well and I jumped pin 50 and C (on the SBIR) and the car started !! (Recently failed seatbelt interlock relay because I replaced the fuel pump??)
My questions now are:
1. Should I leave the SB Interlock relay(SBIR) in? Yes leave it there but look at the two large yellow with red and yellow leads and connect them together thus effectively eliminating the relay all together
2. The seatbelt light never worked .. haven't check the bulb or CCA yet, could it be related to the SB Interlock relay(SBIR)? Yes but with the relay bypassed who cares about the seat belt light. You would have to reconnect the plugs into the cushions and the seat belt holsters
3. E-brake light never worked.. have checked the bulb and have continunity to BRN/YEL wire to pin A (SBIR), could it be related to the SB Interlock relay?
The emergency brake wire just uses the interlock relay as a terminal point on its way to the light and functions through the turn signal switch. Just make sure that the two wires are making good connection with one another and make sure that you have a good four prong relay installed for the turn signal
4. Oil Pressure light never worked.. haven't check the bulb yet, could it be related to the SB Interlock relay or because I have a guage?
No it functions independently. Just make sure that the red and white power lead has power at the bulb the other side the green and red goes directly to the switch via the relay board
5. Defrost light on console never worked..haven't check the bulb (looks ok) or wires yet, could it be related to the SB Interlock relay?
No this wire (black with blue) is wired into the loom that powers the instrument lights and console lights (if you have a console) check the black and blue for power when the instrument lights are on and check the ground lead behind the relay board in the engine compartment
I will check the bulbs and wiring soon, just wanted to get your opinion if this could be related to the SBIR.
Also the buzzer next to the SBIR works on the passenger side (i.e. buzzes when the passenger door is open and the key is on) but not the driveres side door (but the interior light works fine with both doors). The seat sensor has been connected and disconnected with no difference. I would check the connections at the door switch there are several on each switch.
Do you have schematics of the SBIR and/or the 74 style buzzer (not in Haynes). I would rather replace a "suspect" relay (but rather not pay $52 to guess) before I pull things apart . Again I would not worry about connecting the relay. It is really a useless device
Thanks,
Tim
I would advise connecting everything as original if you have an original concours entry however as a edit to my "useless device" statement!
Thanks for the info and quick reply !!
basically SBIR = tits on a bull (gotta love our government helping us live a better life)
I'm an engineer and I can't help myself makeing things work that don't (but should).
basically SBIR = tits on a bull (gotta love our government helping us live a better life)
I'm an engineer and I can't help myself makeing things work that don't (but should).
Edited my reply above...
2-OH!
Thanks for the info and quick reply !!
basically SBIR = tits on a bull (gotta love our government helping us live a better life)
I'm an engineer and I can't help myself makeing things work that don't (but should).
2-OH!
QUOTE(pin31 @ Jan 31 2007, 04:27 PM)
Thanks for the info and quick reply !!
basically SBIR = tits on a bull (gotta love our government helping us live a better life)
I'm an engineer and I can't help myself makeing things work that don't (but should).
QUOTE(2-OH! @ Jan 31 2007, 07:42 PM)
Edited my reply above...
2-OH!
QUOTE(pin31 @ Jan 31 2007, 04:27 PM)
Thanks for the info and quick reply !!
basically SBIR = tits on a bull (gotta love our government helping us live a better life)
I'm an engineer and I can't help myself makeing things work that don't (but should).
Thanks 2-Oh good suggestions and a place to start
If it is a concours car, then I would open the SBIR relay up and crimp the contacts for the starter circuit together. Then all the other stuff would work, and it would LOOK original from the outside. But it would start every time.
I think I will open it up just to look inside....
I guess nobody has a schematic??
I guess nobody has a schematic??
Thread resurrection : 
After extensive searches I couldn't come up with a concise description of function, wiring diagram isolation, & fault diagnosis of an intact SBIR.
Only the recurring "how to defeat" inquiries ~
So on a 74 with intact SBIR, there are retractable seat-belts with sensors in the receivers.
There should be a pressure sensor in the seat cushion
& on all cars there is a seat belt light on the dash.
How is the logic supposed to operate?
Open the door - you should hear a "door open" buzzer (part of the relay block)
Will the dash light illuminate? or does it need a key in Ignition?
If you sit in the driver seat & close the door the buzzer will stop.
Presumably if you insert the key the dash light WILL illuminate
If you try to start the car ...what happens ? Nothing ? Noise (from relay)?
If you latch your seat-belt, the light on the dash goes out & if you key the ignition it will then start?
What am I missing?
Should you be able to hear the relay triggering?
After extensive searches I couldn't come up with a concise description of function, wiring diagram isolation, & fault diagnosis of an intact SBIR.
Only the recurring "how to defeat" inquiries ~
So on a 74 with intact SBIR, there are retractable seat-belts with sensors in the receivers.
There should be a pressure sensor in the seat cushion
& on all cars there is a seat belt light on the dash.
How is the logic supposed to operate?
Open the door - you should hear a "door open" buzzer (part of the relay block)
Will the dash light illuminate? or does it need a key in Ignition?
If you sit in the driver seat & close the door the buzzer will stop.
Presumably if you insert the key the dash light WILL illuminate
If you try to start the car ...what happens ? Nothing ? Noise (from relay)?
If you latch your seat-belt, the light on the dash goes out & if you key the ignition it will then start?
What am I missing?
Should you be able to hear the relay triggering?
Maybe this helps. From the 1974 S&T manual.
PS its not a relay. There is a circuit board inside.
PS its not a relay. There is a circuit board inside.
Awesome thanks Jeff
Ive never seen that before, S&T manual ? Service & training?
So that is the logic... I see that E-brake is a dotted line?
Never even considered that oil pressure was in the mix.
No mention of door contacts or the buzzer, it must consider that separate.
Ive never seen that before, S&T manual ? Service & training?
So that is the logic... I see that E-brake is a dotted line?
Never even considered that oil pressure was in the mix.
No mention of door contacts or the buzzer, it must consider that separate.
My '74 had the SBIR intact when I bought it in 2009. I was stunned that even the passenger seat had a load sensor circuit -- and it worked!
I eventually followed the "defeat" instructions on here, prior to updating the seat belt mechanisms to something more modern (seatbeltplanet).
IIRC, you'd still hear the fuel pump as the ignition switch rotated to "on" but there was only a click when you rotated to "start"
I think the first few mechanics who worked on the car hated me for it.
Usually they'd leave the driver's belt buckled the entire time they had the car and just climb into the seat on top of it.
I eventually followed the "defeat" instructions on here, prior to updating the seat belt mechanisms to something more modern (seatbeltplanet).
IIRC, you'd still hear the fuel pump as the ignition switch rotated to "on" but there was only a click when you rotated to "start"
I think the first few mechanics who worked on the car hated me for it.
Usually they'd leave the driver's belt buckled the entire time they had the car and just climb into the seat on top of it.
QUOTE(914werke @ Jun 7 2023, 10:41 AM)
Awesome thanks Jeff
Ive never seen that before, S&T manual ? Service & training?
So that is the logic... I see that E-brake is a dotted line?
Never even considered that oil pressure was in the mix.
No mention of door contacts or the buzzer, it must consider that separate.
Find it here: https://bowlsby.net/914/Classic/zMan_1974_2...iningManual.pdf
Anyone have an isolation for the wiring diagram & or flow chart? 
QUOTE(914werke @ Jun 8 2023, 05:56 PM)
Anyone have an isolation for the wiring diagram & or flow chart?
Rich
Reopening thread. Did you ever get a wiring diagram for under a 74 passenger seat? I bought both from prospeo’s and the interlock and the other box are not on there’s. I have the yellows joined but wondering what the others are for?
Kevin
The others are "for" nothing. They used to carry signals that the relay needs, but the relay did not affect them at all. So you'll get a "switched power" wire going to the relay, and another "switched power" wire crimped into the same connector going somewhere else. That effectively is carrying the switched power to the next thing, and completely ignores the interlock relay.
--DD
--DD
Not following what you are describing Dave? As Jeff mentioned the lrg box (under pass seat) is a logic circuit (if and or then) not a relay (simple switched pwr). I was hoping to locate a current flow / wire diagram of that circuit but the S&T only provides a simple block graphic.
I recall opening one in the past. Seems to me it’s a circuit board with transistors and similar electronics on it. I.e. “Logic board”. An EE could probably develop a schematic for it.
QUOTE(914werke @ Oct 1 2023, 10:58 AM)
Not following what you are describing Dave?
The wires that aren't the thick yellow starter wires going to the relay socket. The relay does not affect those wires in any way; it does not change the current/voltage going through them. It only acts as a switch to disable the yellow starter wire. The circumstances where it does that may be more complex, but the only thing it actually affects is that yellow wire.
--DD
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