MG Car Repair/radiator fans
QUESTION: Barrie. I recently asked a question about my rad. fans. I left out some facts. The car is 79 MGB USA. My fans do not work. The resister for the distributor was bad. The new part that I ordered was substituted with a 5 prong relay. When I tried to wire it, my gas gauge, tack and temperature gauge did not work. I am not sure if I have the right part or if it needs to be rewired a certain way. Could you help me.
ANSWER: Hi Don. Thank you for giving me the additional information that I needed.
It would appear that the original relays are no longer available, so modern units are being substituted.
I have attached a document from Moss Motors that explains everything.
You only have 4 wires and the relay has 5 terminals. They must be connected as follows:
86 = White
85 = Black
30 = Brown
87 = White with a Brown stripe.
Your relay has a fifth terminal marked 87a. Do not connect anything to it.
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QUESTION: Barrie. The reason I'm confused is that there are only 2 wires available from the old resistor.One is white with a brown stripe,the other is solid green. I wired the new relay from the w/b 30 to the 37a green and lost my tach etc. Where do I find the white,black and brown wires that you refer to. Thank you Don
ANSWER: Hi Don
I am having trouble understanding your problem. If the resistive wire was faulty, why did you buy a new relay? And what has that got to do with the radiator fans?
The ignition is supplied via a white wire from the unfused side of fuse #3. It changes to a pink resistive wire inside the loom. It then changes colour again to white with a light green stripe before exiting from the loom.
The tacho and temperature gauge are both supplied with power via green wires from fuse #3. I suggest you check this fuse.
Keep the dialogue going. We will sort this out eventually.
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QUESTION: Barrie. I thought my fans did not work because of a blown fuse.I replaced the fuse. When I jumped the hot side of the ressitor to rad. thermo. plug my fans ran. Ergo bad resistor, I thought. I have since repeated the process, same result.I now know that it was just a set of circumstances. I have no power to my rad. thermo. switch. I checked the continuity and the thermo switch is open. I checked all my fuses with a continuity tester and they are o. k. I found one inline fuse with a grey wire that had no power. Fuse is o.k. Where do I start looking for the open thermo. wire. Thanks Don
1) The only resistor that I am aware of is the resistive wire between the coil and the ignition switch.
2) I cannot find an inline fuse with a grey wire anywhere in your wiring loom. Fuse holders have 2 wires. What is the colour of the other wire?
Have you checked the inline fuse holder for the fans?
One side of the inline fuse holder goes to the non-fused side of fuse #3 (White/Brown).
The other side of the fuse holder goes to the thermostatic switch in the radiator header tank (Black/Green).
All the items that have stopped working are powered via the FUSED side of fuse #3.
The power to fuse #3 comes via another (White/Brown) wire from the ignition relay. Perhaps the relay is failing or there is a bad connection at the fusebox. Please note that both the wires to fuse #3 are the same colour, so it is easy to get them mixed up.