• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Ignition light on/ key off

Share this page

C

CaptMorgan

Freshman Member
Offline
Hello MG Forum...
On my '79 MGB, the ignition light remains on after the key is off, and out! When this happens, the brown wires to the fuse box are hot, as well as the white/brown. If I disconnect the white/brown (signal?) wire from the starter relay (one closest to the front, maybe ignition relay) the light goes off, and stays off when reconnected, and it's not hot at the fuse box (browns stay hot). I replaced this relay (with what I think is a new one, from PO) but problem remains. I read the thread about the alternator diodes, but as mentioned problem clears as described above. (I did replace the ignition coil recently and screwed up the polarity... causing the tach to act weird until corrected.) Is this also a alternator problem, or do I need a new ignition switch, or what? (Oh yeah, PO installed after market electronic ignition, so there some weird wire splicing going on.) If you understand Lucas electronics, please help!!!

Thanks!
 
If you understand Lucas electronics, please help!!!

That leaves about 99% of us out.
Just a quick quess, a sticking relay. Get a soldiering iron and soldier all those weird wire splices. Wayne
 
Wow, that is indeed a weird problem. /ubbthreads/images/graemlins/confused.gif Can’t say I’ve ever heard of anything like it and I thought I’d seen just about everything on my 78B. It might be the Alternator and it might be the ignition switch itself.

First things first – do a diagnostic of your charging circuit. There is a great tech tips section in the back of the Moss Catalog that you might find helpful. If that checks out ok – then I would start taking voltage measurements with the ignition switch on and off and start comparing them to the schematic for your vehicle found in both the Bentley & Haynes manuals. Any suspect circuitry – I would do an in-depth continuity check on with an ohm meter.

Like Wayne, I too suspect that something is sticking like a relay or perhaps a carbonized contact that won’t release. You might check the anti-run on valve circuit as it turns on for a short period of time after you turn the ignition off. Otherwise, it might be a negatively activated circuit that is short to ground someplace that is keeping things live.

The bazaar thing about electronics (especially intermittent problems) is that the simple act of poking around trying to figure out what is going on – might make the problem go away. That is why I suggest cleaning up contacts and/or re-terminate suspect connections as you go over the cars circuitry.

Good Luck!
/ubbthreads/images/graemlins/cheers.gif
 
Mechanical problems = minutes to diagnose, hours to fix

Electrical problems = hours to diagnose, minutes to fix

Translation: patient tracking of circuits and testing of components are the way to track this weird one down. I too suspect a relay but that comment about a spell of incorrect polarity is worrisome.

P.S. -- like your rum Capt!
 
When you say ignition light are you talking about the red light on the left of the dash? I just bought an MGBGT also and that is what mine is doing.
 
Aloha CaptMorgan,

Although I'm not a MGB owner, Lucas has been fairly consistent in the color coding of their wiring. The brown heavy gauge wires are connections between the battery (unfused and always powered) and circuit items such as starter solenoids, starter relays, control box (voltage regulator). If the red ignition light is on when the the ignition switch is off, I would guess you have something in the starter circuit grounded resulting in current flow. Perhaps a stuck relay in the energized position as previously mentioned. The hot brown wire to me indicates that there is current flowing through it. If not corrected it will drain your battery and may also damage the wiring harness. Good luck in tracking this down.

Safety Fast,
Dave
 
Back
Top