MGB: Key buzzer fix 78B

I don't care too much for the seat belt buzzer but would like a key reminder buzz. Just last week I almost left the keys in the ignition leaving the B to go into the store. So where to start? I have an extra buzzer somewhere in the tool box if need...

I think you can do it since you have a late model car, The '74 or later cars' anti-run-on leads from the igniton switch would be used along with the drivers side door switch and a relay. I'd use a relay just to make sure you're not drawing too much current through the ignition switch contacts. Working on a diagram. I'll update the post when it is complete.

Here's what I came up with. The wiring in the light blue is the additon. I added a diode to prevent a sneak circuit back through the lamp. If you can't see them from the picture, the existing wires are:

Fuse to lamp - [s]pink[/s] PURPLE[/b]
Lamp to switch - [s]pink/white[/s] [b]PURPLE/WHITE
Ignition switch to anti run on valve - slate (gray)

The diode can be picked up at Mouser, DigiKey etc. I'm sure Radio Shack has power diodes also. You could probably get away with a signal diode, but the power diode leads are more robust.

The way this is supposed to work is that power is applied to the anti-run-on switch when the key is in the off position, then when you open the door the circuit is completed and the buzzer sounds. According to my information the power is only applied to the ant-run-on switch when the key is inserted and the ignition is off.

I just checked out a 6-18V piezo buzzer form Radio Shack. It draws 10 milliamps. If you buzzer draws that low of a current then the relay is not necessary and the buzzer could be wired direclty from the ignition switch to the diode,

Larry,
I got a 12 volt buzzer from RS and it has three wires...any idea on how these should be wired... there is a somewhat unclear diagram on the plastic wrapper the buzzer comes with. Not sure why you would need three wires. Thanks!
Frank

Frank

Three wires? Maybe power, ground and an enable. Do you have the part number?

I believe it is this one the 80dB chime 273-071.



Thanks and your explanation...power ground and enable sounds right.

Frank

Frank

I'll wander over to the local RS after lunch, check it out, and let you know.

I think you twist blue and black wires together.

Frank

The blue lead on the Radio Shack buzzr/chime (p/n 273-071) is indeed an enable. Here's a diagram on how to hook it up

PULLED THE DIAGRAM I FOUND AN ERROR IN IT

Here is the updated schematic. I tested the circuit out using batteries and diodes. I was concerned that the diode in the enable lead (dark blue) of the buzzer might cause the buzzer not to sound. That was not the case. I haven't checked this out in the car, but the information I have about the way the ignition switch operates indicates to me it should work.

One note - the wires coming from the buzzer are awfully skinny - looks like 30 AWG or smaller. If it were me, I would mount everything inside a "hobby box" - you can get this at Radio Shack" and have more robust wires, 20 AWG or so, coming out of the box and use those wires to tap into the MGB's wiriing harness.

As to cost, the buzzer was about $10.00 and a package of 25 1N4001 diodes was about $2.50