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MG MGB Technical - how to bypass sequential seat belt control

Hey, guys, I've been having weird problems starting my early 74 MGB and need your expertise. I've got the new high torque starter, new ignition switch, replaced the 2 six volts with a new 12 volt battery, and the starter doesn't do a thing. When I hit the switch, all the lights come on correctly but the starter just sets there, no clicking or anything. I've cleaned the ground strap, tried a different starter relay, tried a new positive cable and it still won't do a thing. Next on the list is to bypass the sequential seat belt unit.
It was screwed to the backside of the metal plate that holds the console in place. I've got it out now and setting on my coffee table.
I searched the archives and found 3 or 4 threads about it, but I want to make sure I'm getting this right. One thread talks like there's a wire to cut that will cut the power to the entire seat belt circuit. Another thread talks like I need to put a jumper somewhere. What is the best way to totally remove that sequential unit?
thanks,
Ken Thompson
early 74 MGB
Kenneth Thompson

Hahh I had the same with my 74 midget. Its real easy to bypass both the starter relay an the seat belt stuff. From the ignition switch there is a (red/white) wire going to the seat belt box.Then from the box there is a (yellow/pink)wire to the starter relay(Join both together).At this point at the starter relay you will need a double female to connect the Brown/white and the Yellow/pink wires and bam! you never have to worry about the problem again! The early cars have just have a (red/white) wire from the ignition switch right to the starter solonoid. You could just run a 14 or 12 guage wire right to the starter solnoid from the switch. I found all this info in the MGB haynes manual.It gives you more info that My haynes Midget manual. Both manual come in handy when you are stumped on a MG problem.
James

As James says to bypass the sequential seat belt unit you need to jumper pins 1 and 3, white/red to yellow/pink. However *don't* bypass the starter relay as well or you will damage the ignition switch. The relay is there to protect the switch from the relatively large current of the solenoid. It also puts more wiring and connections in series with the solenoid and as such is more likely to cause non-cranking problems if the battery is a bit weak.
Paul Hunt 2

Ken,Sorry Paul is right keep the relay in place. My problems started at the seat belt box. Then my reley went out so thats why I bypassed both. I've had no problems so far and the last bypass at the relay was over a year ago. The relay is to protect the seat belt box when the starter was kicked over sending all the power to the starter. And yes a relay is to portect a small switch(Ignition)to power a big one starter.
James

FWIW I also have to say that the relay doesn't protect the sequential unit, which remains powered all the time, just the ignition switch.
Paul Hunt 2

James, Va beach Va-

Replacement relays are available at local chain auto parts stores for about $5.
Kimberly

Thanks for all the great response. I tried bypassing the relay and it drained the battery down to nothing, so I think I'll leave it in place. I found a relay off a triumph GT6 that is identical to the MGB relay so I have a spare.
Are there other circuits tied into the seat belt circuit? If I take the box clear out and just jumper across terminals in the plastic connector, will that cause other circuits to go out? Where the plastic connector comes out of the wiring harness I could easily make a small jumper from 1 to 3 but what about all the other terminals in that block?
This problem has been on and off for about 3 years. First I got the new starter, and it worked fine until summer. About a year ago I put new cushions, diaphragms and vinyl on the seats and took the round white switches out of the seats. The problem occurred on and off but I was always able to get it started after several attempts. That's when I got a new ignition switch. The switch is an earlier model that doesn't have the purple wire for the seat buzzers. I simply left that wire disconnected, and the starter system worked fine until October. On one of our club drives the engine quit because of the rotor and distributor cap, and then the starter problem returned. We got hit by several blizzards and my MGB just set there until March. In March, suddenly the starter circuit worked and I got the engine to run and drove it for a week. Then the starter problem returned and that's when I started looking closer at the wiring diagrams for problems such as this sequential box.
So would it be okay to fashion a jumper across the terminals of the white plastic connector coming out of the wiring harness?
thanks for all your help.
Ken
1974 MGB
Kenneth Thompson

THanks Kimberly But,Im gonna stick with the set up I have in place. As for the relay the early pre 67 cars didn't have a relay for the starter (as said before. Since the later cars with the seat belt control had a starter relay I thought it might have something to do with the seat belt conrol. Looks like the UK cars had a starter relay as well on 1969-81 cars ONLY for the starter.Thanks for clearing that up Paul. If I remember correctly didn't Ken have a problem? LOL!
James

WAIT! Didn't MGB have two buzzers? One for the seat belt and one for the key reminder right? Man this is starting to get to me! I think my 74B had two buzzers.Ken you best bet is to remove the seat belt box bypass, or whatever. If you are doing a full restoration and want original look then try to get the box working again. The next time you try to start her remove the brown/white wire from the solonoid and see if you are get 12 volts or use a test light to see if it lights up with the key turn all the way to start. (You'll need a friend)You might also have other problems it looks like. So just trace ALL wires and study you manual some more. Lucas is not that evil.
James

If you don't care about the seat belt reminder light and the buzzer you can unplug the plug to the module and connect the #1 WR wire to the #3 YK wire. I soldered bullets on mine and connected then with a bullet connector. If you wish to have the seat belt buzzer and indicator working you may find the under carpet wiring to the seat switches is bad needs repair.

I don't think it's a good idea to bypass the start relay and run the wires to the solenoid in cars that have a start relay unless you install a heavier wire from the switch to the solenoid. The cars without a start relay up to around 69-70 had heavier wiring than used in the later cars. With a heavier wire the contacts in the ignition switch will have a shorter life.

Clifton
Clifton Gordon

There was only one buzzer for both seat belt and 'key in, door open'.

The starter relay was nothing to do with the seat-belt system, it was introduced one year after the pre-engaged starters as the solenoid on those takes more current than the older remote type for the inertia starter, and hence was putting a heavier load on the ignition switch, as well as making the solenoid more susceptible to low battery voltage. The relay reduces the load on the ignition switch and its connections to a very low level. As such the starter relay was provided on UK cars as well from the same date, and those care didn't have a seat-belt warning until much later.

Definitely NOT a good idea to bypass the starter relay, then. But if bypassing it drained the battery then the wrong connections must have been linked anyway.

The seat-belt unit has no other important connections, all the others are to the sensors and voltage and ground supplies. Of course if any of the pins come *into contact with* other circuits you could get undesirable and confusing effects.

As to the non-starting, then if you hear a click from the starter relay or a clunk from the solenoid then the problem is nothing to do with the seat-belt unit or its wiring anyway. And if you don't get either a click or a clunk, then it could be the seat-belt unit or connections, but then it could be the ignition switch or relay and their connections. If it happens again, stays long enough and you have the time, check for 12v coming from the ignition switch on the white/red (switch turned to crank), and 12v arriving at the relay on the yellow/pink. Then check that there is *not* 12v on the black at the relay, which would indicate a bad ground. If you get all those then the relay is bad.
Paul Hunt 2

Thanks again for the tips and advice from everybody. No, this isn't a restoration, and I don't need the seat belt buzzer hooked up.
The starter relay has 4 terminals: C1, C2, W1 and W2. I jumpered C1 to C2 and W1 to W2 and it ran the battery down. But I've reinstalled the relay and I'll just leave it there. The new ignition switch DOES have the heavier wiring, because it is the earlier switch that doesn't have the purple wire. But it works just fine, the principal is the same on all the cars.
I think I'll jumper the white/red to the YK wire and take the buzzer and box completely out of the car.
We're getting another late spring storm with rain and a forecast of possible snow, so it will be a few days until I can work on it again. But I trust that this should solve the problem.
thanks again,
Ken
1974 MGB
Kenneth Thompson

Ouch! Jumpering C1 to C2 *should* have permanently engaged the starter, which *would* run the battery down pretty quickly, but I'm sure you would have noticed!! Likewise jumpering W1 to W2 would have caused a major short as soon as you turned the key to crank and burnt the loom, it wouldn't have cranked the engine either!!! I'm wondering if you actually bypassed the *ignition* relay in that way, where jumpering C1 and C2 would have powered the ignition which would run the battery down without you being aware other than if you happened to notice the ignition warning light and fuel gauge. However jumpering W1 and W2 would still have caused a major short when you turned on the ignition - if the battery wasn't flat by that time.

If you *really* need to bypass the relay, and I could only recommend it as a 'get you home' measure, you need to link the white/red from the ignition switch and the white/brown (brown/white on some cars) to the solenoid. Originally these would have been on W1 and C2 repectively, but may have been moved round previously (swapping W1 and W2 over, or C1 and C2, has no noticeable effects). Leave the brown and black (C1 and W2) alone.
Paul Hunt 2

This thread was discussed between 22/04/2007 and 25/04/2007

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