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MG MGB Technical - What did I touch & where? New Problem

Okay, the ole' "its always something" came up last night while replacing heater control valve on 80B.

Besides needing to hunt for the perfect tool to remove the bolts from heater control valve, as sockets and boxends don't fit; I now need to figure out what I managed to touch, disconnect or short out while doing the control valve replacement.

The control valve replacement appears to be fine, but when I got into car to start it after topping off the cooling system, I notice something wrong.

Now the tach, temp gauge, gas gauge don't work. Also my right headlight is out. Everything worked before the valve replacement.

I recall these gauges possibly being on the same circuit, but I looked around distributor, coil, etc., for my possibly knocking a wire off. My shop lights are so poor, a tire could have rolled out the garage and I might not see it.

One other little hint or issue: When starting the car in the past, the tach takes a few seconds to respond to the fact that the engine is running.

So there may have already been a loose connection before, now it is looser or off.

Thoughts on where I should be looking, or did I simply blow a fuse?

Now that it is daylight out, I may have better luck looking for something lying about that should be connected to something.

More later, of course; as its always something!
R.W Anderson

some tach don't seem to work straight away so don't worry about it tap the glass once the engine is running and it should start again

temp and fuel gauge might share the voltage stabiliser

or it could be something off the ignition switch

one headlight might just be wiring or bulb (I don't know if the later ones were fused but the early ones weren't fused)

in the Driver's Handbook you'll find wiring diagrams or have a look at Paul's web site for diagrams (mgb-stuff)

ETA: these little problems will crop up on a car used so little previously but you using it now will find and sort them a lot faster so carry on
Nigel Atkins

ETA:
ignore what I put about headlights not being fused as I might be confusing it with Spridget headlights, again the Driver's Handbook will tell you what's on which fuse
Nigel Atkins

Instead of something going wrong I'm still thinking I bumped something under the hood that knocked all this out together.

It is one thing to look at a diagram, it is another to locate where that wire is in the car.

More later.

And yes, I really should buy some shop lights.
R.W Anderson

It sounds like you have two problems.

As Nigel says, the supply to the fuel and temp gauges is via the voltage stabiliser, but the tach isn't, so it's somewhere upstream of that. Most likely is a loose/bad connection under the dash, on the green circuit.

Is your headlight completely out, on dip and main beams? If so, it's likely to be a poor connection on the black ground wire from the headlamp. If it's only one or the other, a poor connection on the blue/red (dip) or blue/white (main), or a blown bulb. Check the bullet connectors behind the grill, where the three wires come from the headlamp unit.
Dave O'Neill2

I was thinking more of the wiring diagram will show which items are common to which components connections, the only thing I can think common to all is the ignition switch

but the light might just be a coincidence

you could have disturbed any wires and connections possible - what about fuse box, any coolant splash out any where

put up a photo if you don't get an answer from someone that knows
Nigel Atkins

The answer to the tool is a 7/16 AF or 11mm metric ring spanner with thin walls.

The answer tio the electrics is possibly the green circuit fuse or the connector on the fuse box - the headlight is not common to that circuit and is probably a separate issue. B headlights are not fused.
Chris at Octarine Services

I had to grind down the outer ring of a 7/16" ring spanner to get a replacement heater valve on, but not to get the old one off.

On late North American cars the green fuse controls all the fused ignition circuits except the cooling fan. This includes washers, wipers, heater fan, brake lights and reversing lights so all those would be out as well if it is the fuse or white/brown connection, only some of them if it is one of the green wires that has come off the back. There is a veritable Christmas tree of 4-way bullet connectors in the green circuit, one supplies the branch to the induction heater as well as the branch to the instruments and other stuff. I don't know where that is, but if in the engine compartment you could well have disturbed that.

If the right headlight is out it has to be the bullets by that headlight, or the connections on the back, or the bulb.
Paul Hunt

Okay I went out after reading Paul's comment and I now see the brake lights and backup lights do not work either, and the wipers don't work either.

I taken all the fuses out, spun them around in contacts with the wipers in the on position in case I get some contact. Nothing. I've pulled all the connectors out of the fuse box and put them on and off, nothing.

It has been suggested I get new relays, the black ones on the fender.

It has been suggested I get a new fuse box.

It has been suggested something came loose under the dash.

For the life of me I cannot accept that something wore out the moment I replaced the heater control valve on the block.

And I don't like the method of simply replacing parts until one make things work, but I've been back and forth under the hood in bright daylight and cannot see anything that is disconnected. And moving all the fuses, wires and contacts around does nothing.

I am confused as to what color wire/circuit I should be following through the car.

To check for a contact / connection being off under the dash will require more time tomorrow, so I can disassemble the cover to get up in there.

Thanks for the efforts so far.
R.W Anderson

Now I've gone out and bypassed the fuses with no result to creating a circuit. And yes, the fan doesn't work either. So this implies from reading above it is something in the brown white wire/circuit that goes to the fuse block and to the forward little black relay.

No idea what to check next.
R.W Anderson

sorry I'm a bit lost as to what you mean (i'm often confussed so don't worry)

you're quite right not to just replace parts and components but instead do a logical step by step diagnostics

first I'd check what electrics are working - if none at all I'd start at the battery

just thoughts now:

you might need to check the underside of the fuse box (connections, corrosion, foreign objects)

did you test the fuses work out of the car (not just visual check)?

I might be stating the obvious but do all the things not working need the ignition on, if so and the ignition was switched on I'd start at the ignition switch

is power getting to the fuse box - chase back all the way to the battery if needs be and even the battery (they do sometimes seem to die suddenly)

you could have disturbed something when you did the heater valve or it might be just coincidence

take your time, take photos, drawings and notes don't pull everything apart and then forget what goes where concentrate on one path at a time and fully complete it

good luck, things are better the next day and in daylight
Nigel Atkins

ETA: I put my previous reply before seeing your last post (I was still typing when you posted) but I think my points still apply
Nigel Atkins

except for things on the one circuit all other things appear to work just fine.

car starts and runs fine.

lights all work except the R headlight on low beam and of course the brake lights and back up lights don't work, but then they are on the same circuit as the gauges that don't work, and as mentioned above the fan doesn't work either, but again - that is on the same circuit.

Other things with the ignition switch work, radio, car starting, etc. Turn signals work, but not the wipers - as again they are on the same one circuit.

dark now, so won't look at more things until tomorrow.
R.W Anderson

Erm - is your car one with the separate line fuse below the main box?? If so have you checked that too?
Chris at Octarine Services

yes I've checked the two individual fuses along the right fender below the fuse box, even swapped fuses. no change.
R.W Anderson

If the *cooling* fan doesn't work either then the implication is that the ignition relay either isn't operating or isn't outputting 12v as it should.

However you say the turn signals work, and they are powered from the ignition relay through the green circuit in the fusebox! Either your car has been wired to make the indicators available all the time, like the horns and interior light, which is a naff way of 'improving' the flash rate, or you are missing something somewhere, and have two or more faults.

That is quite possible, don't go expecting a magic bullet, just diagnose one of the things that doesn't work first and go from there. You will need a voltmeter or test-lamp, twiddling fuses and wiggling wires isn't good enough.
Paul Hunt

Okay, when I wrote 'fan" doesn't work I meant the heater fan, not the cooling fan.

I've been outside cleaning contacts and chasing wires, and I was wrong when I wrote the turn signals work, they do not work - the 4way flasher works.

the horn works, the trunk light works, the radio works, haven't looked at interior light. ignition light comes on, haven't noticed if the hand brake light or seat belt lights come on.
R.W Anderson

Can one bypass the ignition relay - safely - by jumping a lead from the wire coming from the ignition (to relay) to the wire going to the green side of the fuse panel, without damaging anything to see if it is the ignition relay that is the problem?
R.W Anderson

also, when checking the fuse panel, i only placed a lead across the terminals where the fuse goes, essentially really only checking the fuse.

i will go out now and place a lead between the wire coming in and the green wires coming out of the fuse box.

more in a bit. but if jumping across and bypassing the fuse box doesn't do anything, does this rule out the need to simply replace the fuse box.?
R.W Anderson

Update:

I disconnected the wires in and out from green circuit on fuse panel and jumped across wires, nothing.

I disconnected the twin white wires and the single white wire from the ignition relay and used a jumper wire between the two clips, and I can get the wipers, heater motor and turn signals to work. I didn't try anything else, as these were things I could hear come on.

I am assuming this means the ignition relay is burnt out???????

R.W Anderson

You really need to start using a volt-meter, or at a pinch a test-lamp!

"I am assuming this means the ignition relay is burnt out???????"

Not necessarily, which is why I say you need a voltmeter or test-lamp.

All you have proved is that there is 12v from the ignition switch, and when jumpered directly to the relay output things start working. That could be be because the relay winding or its contact are faulty i.e. the relay needs to be replaced, but it could equally mean that the earth for the other side of the winding is missing so it can't operate, or the 12v is missing from the other contact so that nothing is being extended through the contact when the relay does operate.

Without using a meter or a test-lamp the only thing more you can do is tap the single white on and off the terminal it came from while the ignition is on, and see if the relay clicks. If not it could be the winding faulty, or no earth. If it does then it could be the contact faulty, or no 12v on the other contact.

You won't know which until you use a meter or a test-lamp.

It could also be the wires on the wrong terminals, if you dislodged something when doing the previous work and you got them back wrongly.

You really need to use a meter or a test-lamp ... or did I say that already :o)
Paul Hunt

And of course while I was doing all this work while at a friend's over the past weekend, both of my multi-meters were back in another town. And I am fully aware that I could have purchased a 3rd multi-meter for <$10, which I may yet do.

There was no chance of (as suggested in the later part of your post) the wires going back on wrong on the relay. The wires never were off. And the ground wire coming from the relay is nearby and appears fine, but I did not test the relay with a new ground wire going elsewhere, which I may do in when back to the car again.

I'll have to await hearing aids before being able to hear the click of a relay, but it sounds like a good test.

So apparently if by-passing the relay isn't proof of a need for a new relay, then I may be driving around with a spare relay in the car.

AND, on the bright side of all this and having realized for quite some time I need more and better shop lights; I installed 3 twin 4' tube lights last night with daylight style flourescent tubes. One on either side of engine bay and one in the front. It is brighter in the garage than outside now. So I'll be able to see better under the hood now, and the neighbors can see more easily what I'm up to.

Thanks.

R.W Anderson

Before replacing the ignition relay I decided to also run a separate ground wire from relay to engine block. No change.

I replaced the relay and all works fine. That was so simple I decided to put in an upgraded rotor in the distributor and replaced the diaphragm in the Zenith carb at the same time. Boy was it dirty inside the carb.

I have no idea if the car runs better.

Oh, and I replaced the headlight.

So, for coincidence record we have 1 headlight burning out and an ignition relay burning out at the same time as I replaced the heater control valve.

Makes perfect sense to have coincidences, because yesterday I replaced the spark plugs and cabin air filters on my Accord, and now my security alarm system goes off on its own after 10 p.m., repeatedly.

Still having fun.....
R.W Anderson

>>1 headlight burning out and an ignition relay burning out at the same time as I replaced the heater control valve.<< commonality - they all get hot :)


>>security alarm system goes off on its own after 10 p.m., repeatedly<<
for this check the charge in your batteries - car battery, alarm siren back up batteries, alarm fob batteries

also check reset/synchronisation procedures in the manual

or water ingress?
Nigel Atkins

If 10pm happens to be the same time you park the car and set the alarm each time it can be an indication of a battery cell going down. The alarm seems to be more sensitive to this than the starter.

If it's always 10pm no matter what time you park and set the alarm that could be radio interference from something else altogether. Try parking it somewhere else :o)
Paul Hunt

Stop working on your cars! You're just creating more work for yourself. Trust me, I know the feeling. RAY
rjm RAY

perhaps it's the house alarm that goes off
Nigel Atkins

I've decided to put tools away for awhile and simply drive cars.

Or stay home, stay out of the garage and have a beer or two.

Oh, and alarm isn't going off as far as I know, but I haven't been home for a couple days, so I'll have to ask the neighbors if they are still talking to me.

Moving car originally didn't help either. Not locking it did help.

R.W Anderson

>>I've decided to put tools away for awhile and simply drive cars.

Or stay home, stay out of the garage and have a beer or two.<<

why not combine the two - we drive out on interesting roads to lovely country pubs and have fresh real ale from the pump (rather than bottles) - your equivalent might be bars and craft beers
Nigel Atkins

This thread was discussed between 09/08/2013 and 19/08/2013

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