Ignition light comes on when there is no key in the switch

[beech07]

Hi,
I’ve had my MGB roadster for 10 years and it has been a joy and have been to Southern Italy via Switzerland
And the South of France twice never let me down.
Recently has let me down, backfiring and finally refused to go. RAC rescue fitted a new condenser and solved the problem
Got me going again but noticed at the same time the ignition light stayed on slightly and flickering and heard the
Fuel pump also ticking but not the same sound as when it is filling the the carbs.
So very strange, spoke to Auto electrical friend who said probably the ignition switch, so got a new one from MG owners spares
And fitted that. No change, have to disconnect the battery to be safe as have been out and found the ignition light comes
On on its own. Reading on the forum suggestions were probably an alternator problem, so yesterday bought a new alternator
From MG owners spares and fitted that, guess what no change. Ignition light stays on and engine keeps running when I take the key out.
Completely baffled, could it be some sort of relay problem? Any suggestions gratefully accepted.

[Charles Farran]

Hi Beech,
Welcome to the forum.
So that one or more of us can assist , it would be helpful if you would let us know the model year of your car & what changes/modifications,if any have been made from the original set up - i.e. does it have the original dizzy set up or have you gone electronic (& if so which)? Is it fitted with an original fuel pump or a modern solid state electrical one? Is it fitted with one or more relays covering starting & ignition & are they correctly wired up? Have the original relay(s) been changed? Has the original wiring been modified by yourself and / or a PO? Has the main jumble of wiring connectors on the inside front wing )been disturbed? Any evidence of any shorting or burnt wiring / loom anywhere?
You say that the car worked okay until recently & then played up & continues to do so despite a new ignition switch & alternator.
A flickering red ignition light arises when there is a difference in voltage between the wires leading to the bulb - this can happen when the alternator / water pump belt (fan if pre electronic) is not at the right tension, a defective alternator or defective battery.
Once the model year is known , then the wiring can be checked to one of the appropriate wiring diagrams which are freely available on the internet.. ( I assume that if it is a model with the 4 fuses in a box that the box is installed the correct way round with the bridge on the "in side" at the top).

Cheers
Charles

[Not_Anumber]

As Charles has said this information is essential. For instance on a late RB car it would be worth checking to see if there was permanent voltage present on the White/Light Green wire from the starter motor to the positive side of the coil which exists to bypass the ballast resister only when starting - that wouldnt apply to earlier cars with the simpler unballasted ignition.

A multimeter is essential here. A cheap as chips one from Ebay would be fine, you will only need it for DC voltage. Most will also measure resistance/ continuity.

[Vic Butler]

If it's a late rubber bumper then another fault could be the "run" relay, the front 1 of 2 in the engine bay on the offside inner wing.
However, I wonder if the backfiring etc was not caused by the condenser but something else even though it seemed to cure the fault it was odd that the ignition light stayed on after the condenser was fitted.
Please note that it is essential to quote the year of MG if help is needed.

[beech07]

Hi thank you all for your thoughts so far.
My B is a rubber bumper converted back to metal 1978.
Nothing changed standard fuel pump standard electrical set up distributor etc.
Electrics a complete mystery to me, I am quite capable of doing most things but electrics
Are a different matter.
I’ve checked the fuses and fiddled around to see if there is a loose connection there seems
all ok. Was wondering if the relays are ok, are they the two small cylindrical units fixed to the chassis next to the
fuse board? As you can see really clueless?

[Bumpa]

I think your car, being a late model, has an ignition relay. You say there are two relays next to the fuse board. One will be the starter relay and will have brown and white/red wires attached, the other might be the ignition relay in which case it will have one brown, two white and one white/brown wire attached. It seems from what I read that the ignition relay can cause your symptoms. I found this on mgexp.com and have attached it as a Word document. It didn't copy too well but is readable. It's possible that changing the ignition relay may cure your problem.

Ign Relay.doc

(25.5 KiB) Downloaded 359 times

[Charles Farran]

Hi Beech,

As you say you have a 1978 (original RB) converted to "chrome bumper" , then yours should have a forward mounted radiator with an electric fan. (Prior to the radiator being moved forward the fan was driven by the belt that spins the alternator & water pump.
On these cars there were two relays forward from the fuse box , with the last versions being round (like an old film canister). As Vic says, the one nearest the front is the "run" one i.e. is in use when the ignition is on and the engine running , the rear one is only in use when the starter is being cranked. (There are several threads about these in the technical section in the last 12(?) months). The original round type are no longer available as new stock items, but they occasionally turn up at classic spare sales days etc. All of us who have had MGBs have had these relays play up from time to time & they do cause strange results. (Modern replacements are readily available from the usual suppliers). The originals were robust & also effective in either being "on" or "off". By that i mean that when they were "off" they prevented any stray currents passing through them in either direction. (Yours may be sticking/ breaking down)!
It is worth checking that your relays are connected up to the correct wires (one of the threads i referred shows what goes where). It is possible to mix up the wires that go to the front relay with those from the rear. However, if these have not been disturbed since you first experienced miss firing / non starting , then the problem is more likely to be a faulty relay - substitution is the way to establish this. (You could simply try swapping the two relays round if they are both the same & see if the original problem is still there or changes or goes away)!
As a separate issue, as you appear to still have the original distributor, you may have an issue with the cloth covered earthing wire on the points to the base plate, which may be shorting from time to time & thus causing one of your original problems that might have been partially resolved as it would have been moved when the condenser was replaced. A picture of under the bonnet is always useful as well! - I'm sure others will be along to give more assistance!
Cheers
Charles

[Not_Anumber]

One thing to bear in mind when checking around the ignition relay is that the power to the + side of the ignition coil comes directly from the ignition switch (via the ballast resistor to drop it's voltage). It is not an Output of the ignition relay,
This is actually the trigger to the ignition relay which when enabled applies voltage to other circuits such as the fuel pump, overdrive and wipers that are intended to come on with the ignition. My understanding is that if the ignition relay was simply stuck permanently in the on position then items such as the wipers and fuel pump would have a permanent voltage but this wouldnt result in permanent voltage to the + side of the coil.

You really do need to get a multimeter on the + side of the coil, get someone to start the car, keep it running and then turn off the ignition switch. Assuming you have a ballasted coil you should see around 13 volts whist the starter is operated, falling to a lower voltage when running. When the ignition switch is turned off there should be no voltage present on the coil. Can you confirm this ?

[Michael Barclay]

Hello Beech
I would agree with Vic, Charles and Chris in that I think your problem is with the Run relay.
Try disconnecting the White / Brown wire, connected to either pin 87 or 30/51 depending on how it has been wired. This is the main feed to the fuse box when the ignition is turned on, providing power to the electric fan, ballast resistor side of the ignition and indirectly the ignition warning light. If the problem seems to go away, reconnect the wire and remove the white wire connected to pin 85 or 86, again depending on how it’s been wired. This is the wire from the ignition switch that powers the coil of the relay thus when energized should provide power to the fuse box. Do this with ignition on and hold/listen to the relay to see if you feel /hear a click when you touch the white wire to the relay terminal. From the above you should be able to establish if the relay is working correctly.
As Charles says the original relays are hard to come by but suitable replacements are readily available.
Below is a link to a suitable replacement relay. Both the ignition and run relays are identical so might be worth changing both.

www.12voltplanet.co.uk/standard-mini-ma ... v-40a.html
Hope this helps.
Mike Barclay

[beech07]

Thank you everyone will try by replacing the two relays.
They appear to be identical Lucas relays.Fingers crossed.
Will come back to the forum with an update.