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MG Midget and Sprite Technical - Electrical Gremlins

Can't seem to work this one out and its making steam come out of my ears!

recently rebuild 1960 Sprite
Neg earth converted
Alternator conversion

All electrics work fine except:

Wiper motor seems low powered, struggles to run unless windscreen is soaked or the blades are taken off the screen (then works fine)

The Rev counter goes to 0 whenever:
Wiper motor turned on
Indicators activated (only when flashes)
Brake lights activated

Can't for the life of my work out whats causing all this.
Connections for conversions all seem fine. Can't find an obviously bad earth (may well still be this just getting so frustrated with it now thought best ask others incase I am missing something stupid)

Cheers
D Paul

Hi,


That's an odd set of symptoms!


First reaction is its a poor earth behind the dash, are all the earthing points clear of paint?


I'd run a temp earth wire from the battery to say the rear of the tach and see what effect that has.

The wiper switching is in the earth circuit on an early car, so try disconnecting the black/green at the motor and running a wire straight to the battery negative, if it runs ok then, your prob is deffo in the earthing.


Regards Steve
SR Smith 1

Earthing points are great, cleared out with taps.

Ran a seperate earth for the tacho to the main earth strap of the battery....no change.

I'm wondering if its something in the voltage regulator because of the negative earth conversion and alternator conversion. Might just stick in a junction box and remove it see if that solves the issue.

Its almost as if the draw of the wiper/flasher/brake lights cause the tacho (RVI 2430/01 negative earth late midget type) to be unable to sense any more. It is wired in between the ignition switch and the coil. Rather than between the coil and the dizzy. I guess that might be the next potential change see if that eliminates the interference. Just wish understood what was causing it! Feel like im totally guessing!
D Paul

Steve is far better qualified to tell you which wires to connect together and which terminals to bridge, on your regulator, but the alternator conversion means that you dont need a working regulator. You may want to keep the body for 'originality' or as a junction box but once the guts are removed it makes a handy place, under the bonnet, for stowing a spare set of spark plugs or small odds & sods.
Alan
www.masckent.org
Alan Anstead

Hi again,


I didn't realise that the old VR was still there tbh. Have you still got wires attached to it?



The best way is remove it completely, common all the brown wires, isolate the earth and join the old "F" terminal to the ig waring light wire.



Did you try running a direct earth to the wiper motor switching circuit?



We'll crack this I'm sure.


Regards Steve
SR Smith 1

Direct earths on wiper motor and tacho made no difference.

Got delayed today putting in hardtop rear window and trying to set fire to the car (don't connect the tacho sense to the wrong side of the coil in a moment of madness...). All back on track now.

Away with tr registry and ex works tr3 at castle coomb tomorrow but on weds I shall start again here.

Current plan of attack:
Run a direct 12v to the wiper motor and see if this increases it's power. If so going to be suspicious of a dodgy wire in the switched live (green) cabling.
If not going to remove the VR (currently just a junction box) incase something funny is going on there.
After that.....bin the tacho :p ?
D Paul

Hi,

Stranger and stranger!


Just looked at the wiring diagram in the Haynes book for a Frogeye.


There are 3 green wires off the fusebox..........



One goes direct to the brake light switch.



One goes to a 4 way snap connector (behind the fascia?) feeding the blower switch and the fuel gauge.


This where the drawing looks odd, the 4th wire is shown going to the flasher unit, but appears to join the last green wire somehow which feeds the wiper motor?


It's not clear how this connection is made or is it a factory mistake? as the current path from the fuse would then be duplicated.


I assume that you've added the ig supply for the tach as the car would have had the cable driven tach off the dynamo?


As you seem to have eliminated the earthing side, it must be a problem in the green wiring.


Not a simple case of a corroded fusebox is it?


Good luck!
SR Smith 1

factory mistake or another Haynes mistake?
Nigel Atkins

I assume the wiring diagram is just a copy of the factory one from the handbook or workshop manual.



Just looked at the one for the Sprite 2 and Midget 1, ie 948, and it's the same!


Maybe someone with a handbook or genuine workshop manual can have a look at the drawings in there?


After that, a different fusebox was used and those drawing look correct.
SR Smith 1

Steve
I'll e-mail to you the factory workshop page.
Alan
www.masckent.org
Alan Anstead

https://www.dropbox.com/s/995ndymf3a6kfur/2014-04-30%2008.05.14.jpg

Workshop manual diagram
3 green wires off fuse box
1) straight connection to the flasher unit
2) to four way connector
2a) heater switch
2b) fuel gauge
2c) wiper motor (switch is a switched earth side)
3) stop lamp switch
D Paul

Having just been looking at thr mk3 midget diagrams as the tacho (rvi 2430/01) came out of a negative earth mk3 according to the code numbers there appears to be an online voltage stabilising unit between the panel lamps and the green circuit tree connector that the tacho and the lamps run off....

Ideas ?
D Paul

Sorry not the panel lamps. The fuel gauge....my fuel gauge is pretty sonny but I've got a mismatched gauge and sender at the moment and know thus the calibrated resistances are miles out.
D Paul

This thread was discussed between 27/04/2014 and 30/04/2014

MG Midget and Sprite Technical index

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