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MG MGB Technical - Heater and wiper circuit problem

On my 73B roadster the heater fan and wipers have stopped working. However, the washer and radio (on the same circuit according to the Bentley diagram) are still operational.

So, I'm going to have to start tracking the problem from the fuse outward. The wipers and heater fan failed together while driving in a cold rain, so I'm thinking it could be a corroded connection somewhere that is susceptible to dampness.

Starting at the inline fuse below the fuse block and working my way towards the heater fan and wipers, can anyone tell me where to look for junction terminals that might be the culprit?

Thanks all !!

BH
BH Davis

If the electric washers are OK then the fuse is OK. That goes to a 4-way with 4 wires where one wire splits off to another 4-way, which has two or three wires. One goes to the radio and the other to the heater switch, the heater fan switch then daisy-chains to the wiper switch. So if the radio is still working, *and* it is wired as shown on the diagram (don't assume this), then power must be reaching that 2nd 4-way. The most likely cause is the wire that feeds the heater and wiper switches has pulled out of that 2nd 4-way. Both of these 4-ways will be behind the dash somewhere, it is just a matter of groping around and checking the connections. Only problem is you are likely to disturb one of the other 4-way connectors behind there while doing it!
Paul Hunt

Paul,

THANK YOU !!!! That is exactly what I was looking to find out.

I've suspected the radio is no longer on the original circuit, but will check that out first. Easy enough to do.

I'm going to try and dig into this problem this afternoon. Thanks again for the help !

BH
BH Davis

BH - To get a color coded, easy to read wiring diagram for your car, go to Advance Auto Wire http://www.advanceautowire.com/ click on Stock Schematics and find the one for your car. You can print it out on your own printer, or copy the file and take it to Kinko's (or whatever it is called now) and have them make a full size (11 X 14) and laminate it to give you something easy to follow. Cheers - Dave
David DuBois

David,

Thanks. Yes, I have those and use them regularly.

Car has a mind of its own though. I got as far as confirming power out of the fuse and was getting in the car to start looking at dash wiring. Wouldn't ya know it the wipers and heater fan magically started working when I opened the passenger door. I guess they knew I was about to start a serious diagnosis and decided to start working again to save me the trouble.

Don't ya just live it.

Paul, radio is indeed no longer on that circuit.

Thanks..when it happens again (as we know it will) I'll have enough info to dig into it. I may even get inside the dash and jiggle wires a bit to see if the heater fan stops.

BH
BH Davis

I too have a heater switch problem. For no apparrent reason, the electric dashboard heater switch has 'reversed' itself! Instead of switching it downwards to turn on the fan, in the downwards position the fan is off, and by switching the switch to the normal off position (IE UP) the heater fan works? Anybody got a clue that will reduce the risk of behind the dash surgery? (meaning skinned knuckles, blurred vision, and too many cuss-words for my wife to cope with). - please... no anger management suggestions :-)
R P Shoebridge

R.P.
I always thought that everything in down-under was downside-up to us in the Northern hemisphere.
Could that be your problem.
Well please have a Happy New Year with or without the working heater blower motor.
Sandy
conrad sanders

I suppose it's just possible that something has happened inside the switch to make it work the other way round, failing that someone has been 'avin a laugh and turned it upside down. I've always been able to press the little tabs in on my metal dashes and simply pull the switch forwards on its wires, and so can simply be rotated through 180 degrees and pushed back. But you may need the U-shaped tool to depress them if a padded dash. These have different switches which need one tool to release them from the bezel, and another size to release the bezel from the dash.

If it *is* inside the switch, then simply leave it alone until it fails, as it surely will, then have the job just once instead of twice.
Paul Hunt

Thanks Conrad and Paul. Well, the water in the sink does go around the 'other' way down here in NZ. If we all flushed our toilets at once, do you think the energy drain from the water going around the other way would slow the planet?

Paul, no-one's had a 'play' with the switch, but I think I'll take your advice and just ignore it until it fails 100%. But as you know, windscreen wipers only fail when its raining, so logically, heaters only fail when it's VERY COLD! I live in Akaroa (look it up folks) and it never gets VERY COLD here! It's 34 degrees celcius (look that up too USA friends) this afternoon. The sun sparkles on the water in the harbour. I went for a swim in our cold pool and it was 24 degrees celcius.

Happy new year to all and thanks for the lighthearted tips. Ray.
R P Shoebridge

"windscreen wipers only fail when its raining"

Unless you are blond or grey. After years of having three cars with the indicators and wipers on the same sides I now have a modern MG with them on the 'wrong' sides, with predictable results. Now I've always been considered a lucky beggar and one dry day I turned on the V8 wipers instead of the indicator, the wipers started moving then staggered to a halt. Mindful of the quote above, after I fixed them I ran them for several minutes switching them on and off while dribbling a watering can over the screen, much to the amusement of the neighbours.
Paul Hunt

This thread was discussed between 30/11/2008 and 31/12/2008

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