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Here's one for the ages!!!

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A

als

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Just when I thought I had seen it all (silly me!!)I had a problem that when I started my car (after putting it back together - see earlier post re winter project)the starter kept running after the engine started. There were a couple of other strange happenings of a similar sort going on as well.

After quite a bit of time going over the wiring diagram I recalled an offhand comment that the owner of the service shop that I use had made that in the 76 MGB the car was known to occasionally start by using the handbrake!!! Sure thing!!!

Well, it turned out this is what was going on in my car. With the handbrake on the starter kept going, when it was released the starter stopped!

If you take a close look at the wiring diagram, and don't get dizzy following the wires you will find that the green wire from the handbrake light switch and the red and white wire from starter solenoid end up at the same place. If the green wire is not totally above ground (no resistance) it will keep the solenoid relay coil from releasing. At least that's how it looks to me at this point.

This has got to take the record for the strangest cause of an electrical fault in my limited car experience.

Isn't it FUN working on these wonderful cars???

Al
/ubbthreads/images/graemlins/canpatriot.GIF
 
That's crazy man. That needs to be recorded for posterity. I vote that it makes it into the knowlege base. Under the title of "Little known facts"...lol
JC
 
I had a modern car that would jump out of overdrive (automantic) when the head lights were turn on. Turn out that a bad ground in the license plate lamp was causing the problem.
 
You'll dig this one. The 77 Spitfire has only three fuses. One of them has all of the chassis lighting - dashboard, tail lights, side markers, etc. I was frequently blowing my chassis lighting fuse whenever I drove at night...it always seemed to blow as soon as I would accelerate quickly. Stomp the gas and the dash and tail lights would go out. It took me about a year to discover the source of the problem. Any guesses?....


I found that the plastic fixture that held one of my license plate lights was broken. It would dangle inside of its metal fixture. When the lights were turned on, it was energized. When I stepped on the gas, it would swing backwards and contact the inside of the metal surround--causing a short that was sufficient to blow the fuse thereby causing the dash to go dark.
 
David West,( I suppose that's your name ...? )
Welcome to the playground.
/ubbthreads/images/graemlins/thumbsup.gif
 
Re: Here's one for the ages!!! - Revisited

Soooo.... I and a friend who has been in electrical and electronic fields for over thirty years have spent a number of hours on this problem with no solution. We know for certainty that releasing the hand brake turns off the starter motor...

What we can't figure out is why... I have three wiring diagrams which purport to be for my car (76 Midget - California Car) but none of them show exactly the situation in my car. I have removed all of the emission stuff, including the maintenance interval counters, etc. to make things simpler. Even so, none of the diagrams is right. My cars VIN number is GAN6UG171xxxx.

The crux of the issue seems to be that the white/red wire from the ignition key to the solenoid has about 106 ohms resistance on it with the key off, key on or start. We isolated both ends of the wire from the hardware and got the same reading!!!! So I guess that proves that the wire is not a straight shot from solenoid to the iginition key. One of the diagrams shows it going to a socket with no exit to anywhere labelled the delay buzzer, whatever that is. There is such a socket, with a red/white wire, but not on the same contact as the drawing. One diagram shows the wire going through a diode for an interval counter which is not there. This diode has a common connection to the green/orange wire from the handbrake switch so its a good candidate, except it doesn't seem to exist.

The upshot of all of this is I HAVE NO IDEA WHAT IS GOING ON!!!! Can you tell I'm frustrated??? /ubbthreads/images/graemlins/confused.gif

Can anyone point me at a wiring diagram which would be right for the car I have, and/or provide me with a flash of genious to figure this out.

In the meantime I am driving the car without the handbrake light. This is fine, except that I am bugged by the fact that I can't figure this out.

Thanks
Al
/ubbthreads/images/graemlins/canpatriot.GIF
 
Re: Here's one for the ages!!! - Revisited

Handbrake light?? Pitch it, extra weight. What else do you have that slows you down. You sure you are in the right forum?
 
Re: Here's one for the ages!!! - Revisited

heheee... Yup, pull th' wire and isolate it. Toss th' switch in a pile marked: "OEM JUNK" and Press On!
 
Re: Here's one for the ages!!! - Revisited

I don't have a '76 CA diagram, but looking at the '78 CA diagram I do have I would say that the problem is the brake warning diode. It is the only interconnection between the two circuits that I see. A good test would be to jump out the brake pressure failure switch with the hand brake off and see if the starter stays on until you pull the jumper. If it does it is the diode (or lack there of) if it doesn't then the problem lies elsewhere.

To locate the diode, or where it is supposed to be, trace the green-orange wires from the hand brake switch and the brake pressure witch and see where they meet. There should be a white-red wire on the other side of the diode. I have to assume that the diode is still there because if it were removed completely and simply jumped out then the starter would engage when the hand brake is pulled. If I understand correctly the car will continue to crank when the handbrake is on and the ignition key is turned, but it doesn't crank if you simply pull the hand brake. Please correct me if I misunderstood.

The high resistance may be due to the seat belt sequential control relay / time delay buzzer but I don't know the internal configuration of it so I can’t say for sure. You may also try disconnecting the ballast resistor for the coil and see if the resistance changes, it shouldn't be related, but I wouldn't assume anything at this point. There may be an issue with the way the resistor / solenoid is wired.
 
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