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MG MGA - The value of extra fuses!
|Driving back from Cambridge yesterday evening, out of a low sun so decided to put the headlights on. When we got home, I noticed that the tail lights were not working, walked round the front and the side lights were out as well. The panel lights were still working, so it had to be a fuse because I had fused the side and tail seperately to the panel lamps. Sure enough, when I checked the four way fuse panel I had placed under the dash, the side and tail 25A fuse had blown with a vengeance. I checked the resistance on the distribution side of the fuse and it was low. When I disconnected the red wires from the connector under the bonnet, the low resistance was towards the rear lamps. When I removed all the lampms from their sockets on the tail and number plate lights, the low resistance had gone, so I had a close look at the bulb holders, nothing wrong with the two tail lights, but when I looked at the number plate lamp, I was horrified to see that the red wire was connected to the earth terminal and the black to live! Quite how I had managed to do that I don't know, probably a senior moment, but even more amazing was how the number plate light had worked perfectly alright for over eight thousand miles and through 3 MOT tests! Further tests revealed the answer, the number plate lamp body was electrically isolated from the chassis by paint, grease or whatever. Obviously a bit of vibration had broken that isolation and connected the lamp body to the chassis and effectively earthed the live lamp wire. During testing, merely removing the lamp cover was enough to break the lamp body to chassis connection. But the really important point is, if it hadn't been for that extra fuse I would have cooked the wiring right the way back to I don't know where. And to think that I did at least a thousand miles before I put the fuse panel in!|
Good for you. You must feel very satisfied and smug. I remember the thread clearly and have your wiring diagram in my "to do" pile.
|Graham M V|
|I had exactly the same problem Lindsay, but in reverse!|
I burnt out the front loom and THEN fitted a fuse to the lighting circuit!
Somehow I seemed to have missed out on the feelings of satisfaction and smugness!
|I would go as far as suggesting that everyone of the hundreds of burnt out MGAs would have been saved by simple fusing!|
|Robert (Bob) Midget Turbo|
|I would but im not sure where to put them, Vin.|
|We wired the A with more fuses. We put the fuses on the inside of the fire wall, under the dash. This is NOT the best spot because they are hard to look to see which one to pull, especially beside the road at night. |
I only hope other can learn from our mistake.
|David, is that your dipper switch cable going down in the picture? Mine comes out of the main cable form and goes down through a grommet on the heater shelf in front of the heater box(or where it would be).|
|I have just finished putting fuses in as Lindsay identified in another thread and am very satisfied with it. Thanks Lindsay. |
The Lucas 7FJ 4 way fuse holder does the job nicely but the hole spacing was not quite the same as the holes in the stay for the dashboard 2 7/8" versus 3" so I had to make the holes bigger in the fuse holder to get the screws to go through. Also I fused the feed from the key switch to the ignition and fuel pump separately. I have an extra security link for the fuel pump on my arrangement.
My biggest concern is that the lower Lucar terminals on the fuse holder get quite close to the heater bowden cables which are earthed. I put a small Lucar 3/16 insulator sleeve on each 1/4" terminal on the fuse holder that has no cable attached to be safe. They fit tightly.
The worst problem is that my neck was stiff for a couple of days after the two weekends that I spent doing it upside down. I have also fitted an extra dash below the heater panel with an ammeter, clock and pocket for phone and wallet, just behind the fuse holder. Sorry no pics available yet.
All the feeds to the sidelights, panel rheostat and fog light switch had to be extended to reach the fuseholder, hence the stiff neck.
|John, they must have drilled my stays differently (Moss), I was amazed that they were exactly the right spacing! I like the old fashioned glass fuse holders. Not only are they in-keeping with the car and have the same type of fuse as the existing fuse holder, but they are are a lot easier to get hold of and remove (if you haven't got a removal tool) than the modern blade type. I was just dissapointed that the fault that blew my fuse was not a component failure, but down to the idiot (me) who wired the car up!|
|Here's my installation showing how close the heater cable gets to the terminals but with the 3/16" sleeves as insulators on the lower tabs.
|Side view. I used a 5A fuse for each of the circuits for fuel pump, side lights and the panel lights and 15A for the headlights.|
|Neat job John. I feel you might be sailing a little close to the wind with such delicate fusing, particularly with the headlamp circuit (I am presuming that the fuse is carrying the full load for the lamps and not just a relay circuit). The fuses are protecting the wiring and not the components connected to them, so you can afford to put in a fuse that's just small enough to blow before your wiring gets warm. I found that even a 25A fuse in the headlamp circuit had a voltage drop and ran a bit warm, so I switched to 35A. A 15A could fatigue after a while and suddenly plunge you into darkness, so I think you would be safer with a heavier fuse; unless of course you have done years of nightime driving in your MGA with no problems!|
|Thanks Lindsay. I chose the fuse size to be larger than steady state load and less than the current rating for the wire size on the circuit. The headlamp wiring is 17/18A current rating so the maximum fuse size should be around that otherwise the wiring will be damaged before the fuse blows. A 15A fuse is marginal on the headlamp load but it will take more on peak current before it warms up. I might go for 20A but no more. My Audi has 15A fuses for each headlamp and 15A for all fog lamps.|
This thread was discussed between 04/06/2011 and 14/06/2011
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