[Salad-Dodger]

This is a problem that has been with us since we bought this 98 MGF a few years ago.
When we bought it and brought it home on a trailer it was plonked on the drive and I got to work sorting all the things that you normally sort as soon as you buy a car but the engine just wouldn't come to life at all......until, whilst kneeling down to mend the heater valve cable that was hanging down by the clutch pedal, I spotted a small rocker switch. I flicked that switch and it started with the first turn of the key.
A crafty immobiliser I thought and phoned the previous owner to thank him for not telling us about it. He told me that he had taken the car to an auto electrician to solve this battery drain problem and the electrician had added the switch to the board under the steering column because a relay was not shutting down properly after the ignition had been turned off.

I've been looking about the web on this and apparently it can be down to the ECM not shutting down and the check was to find the pink/brown wire going into the ECM should be checked 20mins after the engine shut down to make sure it wasn't still live. I've done that check and it does shut down.
Now, We do have a "parts" car that is working with none of these faults. Can I swap the board under the right side dash without any problems, or is there some other parts that I'll need to bring with it?
Many thanks in advance! S

 

[Julian Foulger]

By the 'Board', do you mean the fuse box with all its fittings like relays, fuses et al? If so, it will cause no problems although I am not sure why you want to do this.

I have a battery drain so I fitted a battery isolator. It is a naff solution to a problem that I am determined to solve!

 

[Austin2297]

As I see it, there is an assumption that a particular circuit is causing the parasitic drain. You may be right, but you may not be, because it’s an assumption.
The proper way to source a parasitic drain is the remove the fuse from each fused circuit in turn, until the drain disappears - then you have confirmed which circuit is the offender. Bit of a task, but....
Kind regards,
Austin.

 

[Salad-Dodger]

Thanks for that Austin/JF . I'm assuming that the guy who fitted the switch has done a fuse pull check as the wires from the switch have been installed in a very professional way and the wires in question go straight to that board and have been soldered in.
There are a few relays on there. Some are soldered and some, like the yellow one for the heated rear screen are push-in. The heated screen switch has a fault on it as well as it doesn't turn off so I've pulled the relay and the switch.
Your question on why I would want to swap the boards is, it would be the end of the problem altogether. To me, its a bit of a bodge. Another thing is that we have to remember to trow the switch! The switch would go with it as it would no longer be an effective imobiliser switch once the good board was fitted.
It cant be that difficult to do. What I wanted to know is if it was paired with the car in some way with other components.
We will have to sell the car in the future and I cant see me explaining to a buyer that it has a fault and that he or she will need to throw that switch every time they leave the car.

 

[Julian Foulger]

Battery drain like this should not happen. It is possible to diagnose the source but I accept it could take time. Pulling one fuse at a time should identify the problem circuit. Finding where in the circuit the drain is occurring could be either quick if is it is a live wire going to earth could take a little more time.

Pulling the board assumes the board is the problem. You may get lucky but I would not place money on it.

On the relays, they are all pullable including the 'round' metallic coloured relay (cigar lighter).

 

[Austin2297]

As Julian says (and I said earlier) you are continuing to assume, and someone once defined the word Assume as making an ass of you and me.
Why continue to assume when given a bit of time you can do the job properly, and confirm or refute your assumption?
If you are operating on an honest approach with a future new owner then they can only be assured, if you have carried out a thorough investigation.
Kind regards,
Austin.

 

[Salad-Dodger]

Hi Julian/Austin. I think that what I was feeling was that there may have been something on the board that could not have been replaced without quite a lot of problems. It now doesn't appear that that is the case.
The switch install is by anyone's account, a piece of art!
I think the best thing I can do is perform the fuse pull operation myself and also look at where the switch wires actually go to though it looks like the guy may have removed the board to do the work. I'm going to need something to put inline on the negative battery lead to measure a power drop. Perhaps you can suggest something as I think a muti-meter may not be up to it. I have a very good diagram plus the information that Roverlike has posted. I don't think I'll need to take the board out though. I'll report back as soon as I find the fault.
Many thanks for you guidance. S

 

[nocturneblue]

A 10Amp multimeter with the leads connected to the 10A inputs (important you have the leads in the correct multimeter holes when measuring current) should be fine for this sort of investigation. The currents you get looking for this discharge will be well below 10A unless you try and start the car - that would put 200A through the meter and you'd certainly have to replace its inline fuse after that! By the way you are looking for current, not power. They kind of tell you the same information on a fixed voltage system but multimeters generally don't measure power. There is a device called a 'current clamp' which measures current as well - it just clamps around a lead without touching it and senses the magnetic field given off by the current - but I can't see why you'd bother buying one for this sort of thing.

 

[Salad-Dodger]

Thanks for that nocturneblue.
I feel a lot of questions coming on! The first would be a list of what should be live when the ignition is off and the systems have powered down. Of course there are some obvious services that would show they were live like wiper motor and heater fans but things like the heated rear screen or a relay stuck on will be harder to find. I seem to remember someone who had a problem with a central door lock mech as well.
I'll find a quality meter.
Thanks. S

 

[Julian Foulger]

As an aside, if you were to change the fuse box (which has several connectors with many wires going in), it could trigger a myriad of new problems. One thing that I have learnt with cars (especially the MG which I have owned from new since 1998) is that you test, make one change and then test again to ensure that you have not created a new problem, before making a new change.

I have also learnt from experience never to bodge a job - it will involve more work later to rectify.

Best of luck.

 

[Salad-Dodger]

Yes I quite agree. I've had a lifetime of these problems with various vehicles.
The alternator on my 97 XK8 decided to put 22v into the system a couple of years ago and fried a few modules. Took a lot of work finding all the faults on that one as the car was made before the OBD2 standard. The latest one was with my present car, XF 3.0d that has a BMS which was acting a bit strangely. Needed a £140 icarsoft reader to sort that one out.

I've decided that I won't risk my good meter on this MG fault but I've found this meter that may be up to it. Any thought on this would be appreciated. Thanks. S

 

[nocturneblue]

Salad-Dodger,

Actually I think the heated rear screen would be an easy one as:
(a) it'll be slightly warm and would never mist up and
(b) it has accessible terminals you can measure across to see if there's a voltage across it.

I take your point though - there's a bit of unavoidable detective work involved. Essentially all fault-finding involves isolating and/or replacing bits of the system with known good sub-systems in turn until you come across whatever is causing the problem. It may be you can't easily isolate absolutely everything individually - some fuses will feed more than one circuit. That's when you have to stop pulling fuses and start tracing connections and measuring currents/voltages. Remember if something has voltage reaching it (voltage being easier to measure than current as you need to break the line to insert the multimeter to read current) then it might be taking current, whereas if it has no voltage reaching it you can rule it out as taking current without having to break the line to check.

It would be a great advantage for you to find an MGF electrical diagram if you haven't already got one.

 

[Salad-Dodger]

Yes, I do have an excellent wiring diagram. Its from the workshop manual and all pages have been blown up to A3 then laminated before comb binding took place. I was running my own printing business before I retired!

 

[nocturneblue]

S-D,
That multimeter looks fine. You have an 'A' connection hole and a '20A' connection hole. I think the 'A' hole will take up to 2A so might be the better one to use if you're looking for a small <1A leakage. However you can start with the '20A' connection if you like just to see which way the wind is blowing. I may be telling you how to suck eggs here but one test lead will go in the 'COM' hole, the other lead in the 'A' or '20A' hole according to your preference and set the dial to either 2 or 20 DC amps respectively. If you don't get any reading when its inline in the circuit check the multimeter internal fuse.

 

[Salad-Dodger]

No problem. You can never stop learning! Most only use a meter for either volts or resistance.
Its funny, everything looks like its going electric but most of the problems I've had over the years have been with electrics!
Wonder where they are going to find all this electricity.

 

[nocturneblue]

Unicorn poo and rainbows are the favoured technologies going forward I heard ;0)

 

[Man in the Car]

I'm assuming that the guy who fitted the switch has done a fuse pull check as the wires from the switch have been installed in a very professional way and the wires in question go straight to that board and have been soldered in.

I doubt if he did tbh - by disabling the whole of the internal electrics with that switch he has made a quick and easy 'cover-all' solution.

If he had done it properly, he would have more clearly identified the item causing the problem and could have replaced/repaired it. However, doing a proper and full check and trace to the individual component causing the issue would probably have taken considerable time to do, and would have landed the previous owner with a fairly large bill which he may not have been very favourable toward, hence a quick and effective fix to make it affordable.

 

[Salad-Dodger]

I doubt if he did tbh - by disabling the whole of the internal electrics with that switch he has made a quick and easy 'cover-all' solution.

If he had done it properly, he would have more clearly identified the item causing the problem and could have replaced/repaired it. However, doing a proper and full check and trace to the individual component causing the issue would probably have taken considerable time to do, and would have landed the previous owner with a fairly large bill which he may not have been very favourable toward, hence a quick and effective fix to make it affordable.

Quite. That's why I'm going to perform a fuse pull after I've traced where the switch wires go. He must have identified where the problem is before he made his decision as to what part of the system he needed to shut down.
The whole of the internal electrics are not shut down by that switch. Most everything still works when the switch is operated. As the mems/ignition do not work after its switched, that may be an obvious direction but we will see, if it ever stops raining!