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MG Midget and Sprite Technical - Why is the ignition live circuit no longer live?!?

Hi all,

I have searched the archives and now need to ask the question, why is the ignition live circuit no longer live?!?

Two weeks ago all was fine, since then my '78 midget has sat in my garage now I have no working indicators, brake lights, wipers, rev counter and so on.

I am not blowing fuses and all connections to fuse box, ignition, dials etc. appear to be good. Fusebox itself is near new and in good condition.

All connections in boot space and engine bay are on and appear good.

All earths have been checked and appear ok.

Reverse lights switch removed as bare wires were shorting this system on gearbox (done 2-3 months ago without causing any immeadiate issues!)

Hazard lights do work, engine starts and runs fine, courtesy lights, headlamps and horn all work fine.

Stalk replaced to remove this from the equation!

Help, any more ideas from anyone? The sun is shining and I can't bare to see my baby locked away any longer!

Thanks in advance for your help!
D Prince

D,
Time for some serious diagnostics with a VOM and/or a 12V test light. Sounds like a split bullet sleeve to me, but hard to be sure. I am very fond of my VOM, but a test light (easily cobbled out of an old turn signal bulb), has the benefit of putting an actual load on the circuit.

Run through these tests in order and report the first failure you come to.

1. Turn on the ignition and check from earth to the + side of the coil. If you are getting power there, the ignition switch itself is ok.

2. Go to the fuse box. One of the fuses should have a couple white wires on one side and a couple of green wires on the other side. check for power from earth to the green side with the light.

3. There are two of the 4-way bullet sleeves (prime suspects), probably under the dash (not that familiar with the 1500s), that need to have the wires pulled out of all four holes, cleaned, and reassembled. Make sure that all four holes have the metal intact (they tend to split, losing the ability to carry any amperage, although a VOM will frequently indicate that all is fine). While the wires are out, the test light will be able to tell you which of the four wires is coming from the fuse box. After reassembling, use the test light to verify voltage on the other three wires.

4. Let us know what you have found.

David "chase those volts!" Lieb
David Lieb

In an emergency, you can always run a live (maybe fused!) from the battery (non-earth side...) to the dissy live (non-points) terminal... should also run the pump as well as ign...

(BTW - be careful to make sure you can never engage the steering lock at any time when rigging the ignition like this.)

A
Anthony

By the way he indicated that the tach does NOT work, I have to think the ignition DOES work, together with the fuel pump (if present). Sounds like the white circuit is fine (unfused stuff switched by the ignition switch), but the green circuit (fused stuff switched by the ignition) is not. Really has to be fuse, fusebox, or bullet sleeves.. I think ;-)
David "wrong until proven right" Lieb
David Lieb

Thanks for the comments guys,

I have checked the fuse box with a homemade test lamp and get a dim light across the white/green fuse. (Get same intensity of light on my housemates 79 midget across the same fuse, so I think this is correct)

I am having trouble working under the dash, with the 1500's most of the connections are push on spade connectors to the instruments, virtually no bullets at all. There is one main block connector joining front and rear parts of the loom, a second connecting the loom to the stalk, are theses the likely places to test or where the wires meet the spades at the rear of the instruments/switchs?

Sorry if I sound a bit thick here, but electrics are definately not my strong point!

Dave Prince
D Prince

Dave,
Do NOT measure across the fuse. Measure from a good earth (like the battery post in this case) to the green wires coming from the fuse box. The VOM should show full battery voltage (about 13VDC) here, the light should be just as bright as if you were across from the + of the battery to the -.

Obviously, I do not know that much about the wiring of the 1500 Midgets, since I was not aware that they had gone to nice sensible block connectors between the wiring looms instead of the myriad of bullet sleeves used in my 1972.

Because of the actual failures you have mentioned, it is most likely to be at the fuse box. If I have understood you correctly, the car starts and runs, right? If so, the white circuit is working correctly.
The green circuit operates the wipers, squirts, the electric gauges, signals (NOT hazards), brake lights, ignition sweitch illumination lamp, reverse lights, and seatbelt warning. Sounds like the laundry list that you fed us. In order for ALL of that to be down, it almost has to be a problem at the fuse box.
David "more easily said than fixed" Lieb
David Lieb


Dave
If the missing elecktrickery is on the switched live circuit which does not supply the coil (the white wire circuit does this) and the fuse itself is intact (they can look perfectly OK and still be blown/ open circuit) the most likely culprit is the output terminal on the switch.

Test the terminal at the switch that supplies the auxiliary systems, THE GREEN WIRE, reverse lights, indicators rev counter etc but in order for that lot to be down David the switch is a likelier culprit

And the easiest cause of all is a bad connection there or a wire fallen off at the back of the switch

If the switch is fed by a multiplug (1500s totally "terra incognito" to me too David) you can find the inner part of the multi plug after some/several/many years in service loosens internally and lets the female spade in the multi plug come adrift.


Keep us informed Dave
Bill

NO STOP

REALLY, STOP

What I wrote is absolute balderdash

totally off the rails

rubbish

back to David's explanations and forget I was ever in here.

I'm off having a braynestorm

I may be back later

or not

But applying far more common sense than I did half an hour ago I have checked Haynes's wiring diagram and that shows that there is a green multi junction off fuse terminal 6 and that it feeds to the reverse light switch.

Having had this problem in another form a few months ago, I seriously advise checking that the hanging wire from the switch isn't fouling against the chassis near the gearbox and causing a short out.

My friend John's car kept blowing fuses on these circuits which were traced back to there, after the reversing light wwires came adrift

(I really hope this helps more than the previous piffle, but do check the fuse actually allows current to flow wont you!)
Bill

Bill,
You are eventually correct... The ignition switch turns on the WHITE circuit; if the car runs, the white circuit (and thus the ignition switch) is OK. The green circuit is merely the white circuit AFTER the fuse.
David "Already made that mistake once" Lieb
David Lieb

Dave - just to be clear...

The ignition circuit is not fused; this means everything on white incl coil, fuel pump, ... so if you hear the pump clicking, then white is live.

The thick brown from the battery is the feed to the car loom. It finds its way to the ign switch where it connects to white/green for auxillary (fused, for wipers - the in-line fuse on a '73), white for ignition, and white/red for the starter; these connect in order as you turn the key.

Does the starter turn? That means you at least how power to the ign sw.

Next thing (as Bill says) is to confirm that all the above colours are connected to your ign sw, i.e. white/green and white. You need to get you head under the column - maybe take a torch with you). The white ingn wire is actually 2 wires off the same spade - one goes to a connector forward into the engine bay to the coil; the other to a connector back to the fuel pump.

A
Anthony

Good eye, Ant! There are indeed two white feeds on the 1978 Midget ignition switch, one of which feeds the fuse box. Of course, this could be isolated in quick order by the tests in my first post.

Come on, Dave, what is the lamp saying between earth and the wires on the green side of that fuse?
If that does not light, what about between earth and the wires on the white side of that fuse?

David "the curiosity is gonna kill me!" Lieb
David Lieb

Well I searched and searched and got there in the end!

Inside the wiper switch was some goo that had collected accross the contacts, externally it looked perfect but we live and learn,never assume its good until you've stripped it yourself!

Thanks for all the comments they helped me greatly to get there in the end and now I know a whole lot more about electrics!

At least she is now out of the garage :)

My next problem is getting her to run sweetly, at the moment once you get above 3000revs the engine becomes quite gutless! I have tried adjusting carbs, timing, checked plugs and leads!

I think maybe the needle is incorrect does this sound a likely solution?

The fun never stops hey guys?
D Prince

This thread was discussed between 12/04/2008 and 21/04/2008

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