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

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Vic Butler
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Re: Ignition light comes on when there is no key in the switch

Post by Vic Butler »

The relays are interchangeable. I doubt you'll get the original round ones. I got mine from Brown and Gammons but it was the last one.
I've written in my workshop manual which wire goes where on the replacement relays if you get stuck.
Last edited by Vic Butler on Sun Jul 04, 2021 10:43 am, edited 1 time in total.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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Charles Farran
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Re: Ignition light comes on when there is no key in the switch

Post by Charles Farran »

Hi Beech,
Look at the technical thread started 23(?)October 2020 ,on refitting the loom etc (started by me). second page where Vic gives details of the wiring/ terminals of the two relays.
Cheers,
Charles
1980 Roadster
Vic Butler
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Re: Ignition light comes on when there is no key in the switch

Post by Vic Butler »

Charles Farran wrote: Sat Jul 03, 2021 11:18 pm Hi Beech,
Look at the technical thread started 23(?)October 2020 ,on refitting the loom etc (started by me). second page where Vic gives details of the wiring/ terminals of the two relays.
Cheers,
Charles
I'd forgotten about that Charles. It seems so long ago now.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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Charles Farran
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Re: Ignition light comes on when there is no key in the switch

Post by Charles Farran »

Hi Vic,
My grey cells still work,despite the impact of the last 15 months! The actual thread was "Electrics:re replugging & routing the loom" which was in fact originally started by Not.Anumber (not by me) on the 1 October 20 to which we both contributed!!!!!
Cheers
Charles
1980 Roadster
Not_Anumber
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Re: Ignition light comes on when there is no key in the switch

Post by Not_Anumber »

An excellent thread it was too. It was invaluable in helping me fully reinstate my electrics and also usually identified where additional fuses should be added to better protect the loom.
beech07
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Re: Ignition light comes on when there is no key in the switch

Post by beech07 »

Well very interesting fitted yesterday the two new relays and guess what no change
Still have the ignition light staying on flickering and ticking from the fuel pump.

So now have fitted new ignition switch, new alternator and new relays.Not a huge expense but
A lot of worry and my time.

Update to all this and would really appreciate any thoughts, the coil was getting very hot so thought I would
disconnect the wires on the right side there are two wires together white and green, when I separated
them the ticking stopped, I reconnected just one wire and the problem seems to be solved.
However not sure what to do with this other wire have just taped it up.
Think this is safe? Really a complete mystery but the car starts ok and switches off ok and seems completely back to
normal.
Any thoughts hugely appreciated.
Thanks Beech.
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Michael Barclay
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Re: Ignition light comes on when there is no key in the switch

Post by Michael Barclay »

Hi Beech
Separating the two white green wires will help with solving the problem. I think your problem is with the white green wire coming from the starter motor. Firstly just to explain.
Your car is fitted with a 6 volt coil, supposedly to aid cold starting.
During normal running conditions, with the ignition on, power is supplied to the coil (one of the white/green wires) via a ballast resistor,a resistive wire built into the wiring loom which reduces the voltage to 6 volts (although in reality it is nearer 9 Volts.) This is
When the ignition key is turned to the starter position, the starter relay operates causing the starter solenoid to engage and the starter motor to crank. A separate terminal on the soenoid provides 12 volts directly to the coil when the starter is engaged. (Other white /green wire)
My suspicion is this terminal on the starter motorsoenoid is for whatever reason providing a permanent 12 volt feed to the coil and this is feeding back through the ballast resistor to power the fuel pump etc.
If you have a multimeter you can check this out. Measure the voltage on the white /green you taped up. Alternatively use a low wattage bulb if you do not have a multimeter to hand.
Has any work been carried out on the starter motor or wiring recently? If so it is possible the white /green wire has been reconnected to the wrong terminal. Otherwise you will need to remove the starter motor to investigate. One word of warning if you consider go down the route of purchasing a new starter motor, be careful as many of the replacements on offer do not have this separate terminal.
Mike Barclay.
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Charles Farran
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Re: Ignition light comes on when there is no key in the switch

Post by Charles Farran »

Hi Beech,
I'm sorry the change of relays didn't solve your issue - i take it you saved the originals , as it would seem they in themselves were possibly not the cause of the problem ? (if the replacement relay used in the ignition circuit does not have adequate internal diode protection , then put one of the originals back in that position). If you haven't already done so , check that the respective wires that feed the relays are both connected to the correct relay & on the correct terminals - see wiring diagram mentioned below.
You say you removed one of the two WG wires that attach to the coil & the problem went away. As part of the original wiring set up of this year of car, there were two LT feeds to the + side of the coil--- one being at full voltage only when the starter is being cranked & the other being at a lower voltage once the engine has fired & the ignition key released back to the on position. (reference to a wiring diagram for your model year available for free from auto wire - sheet 33 late UK Market Haynes as an example will show you this).
As you also say the car continues to start & run ok despite removing one of these wires -this suggests that the original wiring/ set up may have been changed possibly by a PO. Some owners change the set up to the older approach where only one feed is used at full voltage all the time together with an unballasted coil - possibly as a result of fitting the earlier type of starter motor that doesn't have the additional terminal that temporally supplies full voltage to the coil when cranking.
When the ignition is switched off there should be no sign of any power at the LT+ side of the coil - evidenced by a simple test light probe to the + with the other lead to ground (or use a Voltage meter which should read nil).
If left with a live feed for other than a short while , then you will burn out the coil.
These old cars were designed to give us great pleasure & a little grief from time to time!
Cheers,
Charles
1980 Roadster
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Charles Farran
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Re: Ignition light comes on when there is no key in the switch

Post by Charles Farran »

Hi Beech,

I see that Michael has responded as i was putting my thoughts down , but note his comments very much echo mine!

Cheers,

Charles
1980 Roadster
Vic Butler
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Re: Ignition light comes on when there is no key in the switch

Post by Vic Butler »

I was about to reply after looking at the wiring diagram but Charles has said what I was going to say.
Just one thought. The starter motor solenoid has 3 lightweight wires to it. One is the white/light green 12v feed to the coil, the brown one goes to the light switch and the white/red to the starter relay to activate the solenoid when the key is in the start position. It's a pig to get the rubber cover off the motor to check whether these are on the correct terminals.
Anyway you seem to have cured the fault, just keep an eye on it.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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