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MG Midget and Sprite Technical - 1500 electrics help needed?

After successfully passing the mot last week, my '76 1500 has developed an electrical fault. It's blowing the fuse that supplies reverse lights, tacho, wipers etc.
It doesn't blow it all the time, sometimes you can drive miles with no problem but then it can blow several in quick succession.
I have hooked up a tail light bulb up via the blown fuse and with the ignition on I tried the various switches I have a bright light from all, apart from the wipers which glows from fairly bright to dim with each movement.
Does this tell me that there is a fault with the wiper circuit or have I gone about this all wrong?
Any help appreciated.
Thanks
Kevin
K Grice

I have just noticed that when I try the various switches and the bulb has a bright light, the fuel guage drops to empty. Is this anything to do with the problem?

Thanks
Kevin
K Grice

What you are doing with your test is testing if the lamp consumes less power than the circuit, when the lamp consumes more power than the circuit the lamp will glow brightly, less power it will glow dimly.

So you have tested that the motor uses a lot of power
Will Munns

your test is not totally invalid, a dead short uses a lot of power so the lamp will glow really bright.

First thing you should do is to use a bigger bulb, full beam of a headlight should work better, then go around and wobble all the wiring until the lamp lights really brightly, then investigate around the area for chaffing wires
Will Munns

As Will says, and there have been several reported incidents of shorting out reversing light switch wiring as it passes around/across the chassis and footwell walls.

This can cause these symptoms and a simple visible check for chafing or bare cable ends could solve the question for you
Bill

Thanks both, I have checked the reverse light switch wiring, this was my first thought after going through the archives all looks ok.
Will I don't have a bigger bulb, but I do notice an increase in brightness if i put one switch on and then turn on another. Also if I try to turn on anything else while I have the wipers going the wipers come to a stand still.
Another thing that I have noticed is that the coil gets warm without the car ever being started, is this anything to consider?

Thanks
K Grice

>I do notice an increase in brightness if
>i put one switch on and then turn on another

The combined accessories consume even more power than separately!

>I don't have a bigger bulb

Do you have more bulbs you can wire together (parallel, not in line)

>the coil gets warm
both not warm and warm is normal, it depends on where the cam is - the coil gets warm when the contacts are closed, the contacts may be either closed or open depending.

>Also if I try to turn on anything else while I have
>the wipers going the wipers come to a stand still

Again, this is to be expected, you are seeing the same effect with the fuel meter
Will Munns

Thanks guys, I haven't managed to find the cause yet. but I have found this between the wiring loom and the wiper motor connection. Any ideas why somebody would install these?
K Grice

Sorry here's the image. As you can tell electrics aren't my strong point.
Thanks
Kevin


K Grice

Kevin,

I had the same problem with my 1500, occasionally blowing the fuse that supplies reverse lights, tacho, wipers etc.

I traced it to a metal P clip on the wing inside the engine compartment on the passenger side. The P clip had chafed through some insulation but was only touching occasionally.

I taped it up, replaced the P clip with a plastic one and haven't blown a fuse for 9 months.

Allan
Allan ('76 Midget 1500)

I can't quite see... but if those are units of henrys then those are chokes (electrical chokes) and help reduce radio noise
Will Munns

This thread was discussed on 17/05/2008

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