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79 Radiator Fan Switch

Posted by tomgrigsby 
tomgrigsby Avatar
Tom Grigsby
Ivor, VA, USA   usa
1971 MG MGB GT "The Blight"
1979 MG MGB "The NewB"

What is the procedure for pulling the switch? The book is oddly silent on the subject and mine is probably shot. The PO bypassed it and put a manual switch on the dash (which doesn't work either). I'd like to fix it so I can drive the car for more than 5 minutes at a time. I'll have some wiring work to do - maybe install a relay per the article in the library.

Liz Marcotte
Gray, GA, USA   usa

When I did my switches last year I took the dash off. It's tight under there. If I remember the switches have metal tabs built in and you have to depress them to side them out. Sorry it's not easy, if you can feel the sides of the switch it's kind of like being Helen Keller. Putting them back is easy, you do it from the front, make sure you can get to the wires after they maybe attached to the fire wall so pull the switch easy. Good luck!

James D
beach, VA, USA   usa
1978 MG MGB "The Bee"

Tom, the switch should just pull out of the radiator at lest it does on my 78. There might be a clip holding it in place or just a rubber grommet like mine. If the temperature is getting past or very close to the 1/2 was mark on the temp gauge in five minutes. You might have a clog in the cooling system or the timing is seriously retard..

Note: Originally there was a in-line fuse in the fan harness

James



78..Bee, Leyland A/C (removed), Saturn 95 amp Alternator, Wire Wheels, Lumenition ignition, Weber 32/36, Four speed.





Edited 1 time(s). Last edit at 2011-03-24 10:15 PM by James74.

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29desoto Avatar
Wayne Sanders
Outside Otis, OR - in the woods!, USA   usa
1965 MG MGB V6 Conversion "Carmine"
1977 MG MGB "Ole Yeller"
1979 MG MGB "Kermit"
1984 Chevrolet Corvette "The Green Weenie"
1994 Chevrolet S10 "Lil Red"

Yeah, I think Liz was thinking of the interior heater switch. The cooling fan switch is as James describes it. You can take it out without getting dirty. The rubber grommet around it is like the finger on a glove, and sometime the water doesn't even leak out.

Easy, peasy.



Wayne Sanders
Rose Lodge, OR

"I don't care to belong to any club that accepts people like me"-joined Willamette Valley Club in 2011

77 MGB - Four tone paint - some kind of electronic ignition - hood props - cheap tires - new springs all around - mixture of poly and rubber bushings - original exhaust - fuzzy seatcovers - stereo out of old F150 pickup - virtually no rust - right front wrecked and semi well repaired - just about right for me!

78 MGB - Done right by a good PO, and I only bought it. Tell Jim how nice it is. But I did put in a Datsun 5 speed.

79/65 MGB - Carmine- V-6 - T-5
95% Done. V-6 is a treat, and the five speed is great.
More to do, but isn't there always?

mgv8glen Avatar
Glenn Towery
Dover, Delaware, USA   usa

Make sure you put the relay in with the relay to take the current load off the rad. switch! The new Moss switch is a weak part & I would carry a extra one!

Westley Avatar
Westley Johnson
Redding CA, USA   usa

Hi Tom,

To remove the radiator mounted fan switch, there should be a clip that secures it. Usually the clip is missing and the switch is "hopefully" safety wired in. Remove the clip/safety wire and just pull the switch out of the rubber gromit. You can replace the switch and the gromit at the same time. You can buy the retaining clip, but again most are safety wired in for and enhanced safety and switch retention.

Good luck!

PapaMG Avatar
John Shook
Colorado Springs, Colorado, USA   usa
1979 MG MGB "Tilley"

I have a 79 and can get you some pics if you like. The switch you are looking for is the Thermostatic switch in the radiator. Its at the top with a round grommet that holds it in the radiator. The Thermostatic switch has only two wired connections. The PO on mine did the same thing the PO on yours did. So there is probably a mess of wires running back to the switch on the dash then powered in somewhere. Mine was a mess. I ripped out everything the PO did, then it was quite simple to figure out. The PO put a relay in the mess,,, I kept the relay, it works fine. There may be an inline fuse close to the wiring that runs up to the Thermostatic switch. Mine was bypassed but yours may be in place. You may just have a blown fuse. None the less I would clean it up and wire it back like it should go.. I can get some pics of mine tomorrow.

John



Edited 1 time(s). Last edit at 2011-03-25 10:13 AM by PapaMG.

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Ogre1 Avatar
Allan Ogilvie
Melbourne Victoria, Australia   aus
1977 MG MGB "Greenb"

Its not a fuse it's a circuit breaker. Make sure your not looking for a traditional fuse. They are a black flat looking thingy!

Westley Avatar
Westley Johnson
Redding CA, USA   usa

I forgot to mention one important thing. If you move away from the dash mounted on/off switch you will need to make sure that you close that circuit. If you just replace the radiator thermostatic switch and don't fix the broken dash switch, it still won't work. Hopefully, the DPO didn't hack the wiring too badly when he moved the switch and you will be able to undo the dash switch wiring and correct the circuit.

Good luck.

tomgrigsby Avatar
Tom Grigsby
Ivor, VA, USA   usa
1971 MG MGB GT "The Blight"
1979 MG MGB "The NewB"

Thanks for the responses! My switch has neither a clip OR safety wire! The PO cut the plug off the wiring and ran two white wires around the engine compartment, poked a hole in the rubber thingie behind the BMC and ran it up into the dash. That's as far as I've been so far. He must have picked up power under the dash somewhere(God Forbid), so I'll have to sort that out and then go looking for that inline fuse/breaker hootigator. I'm guessing all the wiring should really be confined to the area between the fuse box and the radiator on the passenger side, right? Liz must be clairvoyant, because I was wondering how to get that switch out of the dash too. Thanks again all.

cfrantz Avatar
Chris Frantz
Mississippi, USA   usa
1957 MG MGA
1964 MG MGB

In reply to a post by tomgrigsby Thanks for the responses! My switch has neither a clip OR safety wire! The PO cut the plug off the wiring and ran two white wires around the engine compartment, poked a hole in the rubber thingie behind the BMC and ran it up into the dash. That's as far as I've been so far. He must have picked up power under the dash somewhere(God Forbid), so I'll have to sort that out and then go looking for that inline fuse/breaker hootigator. I'm guessing all the wiring should really be confined to the area between the fuse box and the radiator on the passenger side, right? Liz must be clairvoyant, because I was wondering how to get that switch out of the dash too. Thanks again all.

He most likely didn't need power to it. The manual switch should just act like the fan switch and connect between the two wires. You could also just leave the switch and wiring alone and just replace the thermal switch with the manual switch also connected. This would provide a backup to the thermal switch when it fails.

tomgrigsby Avatar
Tom Grigsby
Ivor, VA, USA   usa
1971 MG MGB GT "The Blight"
1979 MG MGB "The NewB"

In reply to a post by cfrantz He most likely didn't need power to it. The manual switch should just act like the fan switch and connect between the two wires. You could also just leave the switch and wiring alone and just replace the thermal switch with the manual switch also connected. This would provide a backup to the thermal switch when it fails.

Yup, wires went just to the switch. Turned out the dash switch for the fan was dirty. I cleaned it up and now can manually turn the fans on and off. Looks like I'm back in business. I'll order a proper switch and get it right. I am intriqued by the idea of keeping the switch for a backup, thanks for all the help.

Bruiserman Avatar
Brian Dimond
Orlando, USA   usa
1979 MG MGB
1987 Chevrolet Express Passenger 1500 "Wife's Friends Call It Chester"
2006 Kawasaki zx-14

My PO did the same thing. I bought the thermal switch, left the on off switch so I can still turn it on but wired it so that I can't turn it off by accident. My fan will alwys turn on when it gets hot enough and I can turn it on earlier if I like but I can't turn it off if the thermal switch activates.

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