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Any idea why #3 fuse keeps blowing

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Any idea why #3 fuse keeps blowing
#1
DSVW Dennis S
Ellicott city, MD, USA   USA
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1972 MG MGB GT
Hi, I just bleed my brakes and lubed the 8 or so fittings under the car in in the front end. All was good with the world until I went to go for a ride. Now my Gas gauge, Temp. gauge and rpm Gage do not work. The #3 fuse keeps blowing as well. Everything else seems to be ok. Any thoughts other than don't bleed your brakes next time.

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Re: Any idea why #3 fuse keeps blowing
#2
chris Avatar
chris Chris Roop (RIP)
Pendleton, OR, USA   USA
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What year car is this? Generic advice would be to one by one disconnect the items that run off of that fuse until you have something isolated. Then you look at the circuit from the fuse box to that device to see if you are shorting, and at the device to see if it is shorting.



Edited 1 time(s). Last edit at 2018-03-19 03:21 PM by chris.

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Re: Any idea why #3 fuse keeps blowing
#3
bleteaches6 Avatar
bleteaches6 Silver Member Lee Orphan
Bonney Lake, WA, USA   USA
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1956 MG MGA 1500
1974 MG MGB GT
1974 MG MGB GT
1979 MG MGB Limited Edition (LE)    & more
Have a look at the voltage stabilizer to start

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Re: Any idea why #3 fuse keeps blowing
#4
GMB3 Avatar
GMB3 George Badger
Soquel, CA, USA   USA
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1965 Jaguar E-Type Coupe "1QUICK E"
1968 MG MGB "1QUICK B"
Get a shop manual to start. I believe auto electric or something like that has schematics.


---
GEO

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Re: Any idea why #3 fuse keeps blowing
#5
barry s Avatar
barry s Barry Stoll
Alexandria, VA, USA   USA
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1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
To begin, please identify your car.
You identify 3 separate issues. As suggested, check the voltage stabilizer and associated wiring for temp and fuel gauge. Tach depends on your car year. If the #3 fuse is the 3rd down, it is the purple circuit, always hot but fused (in contrast to unfused brown circuit). Likely somewhere in courtesy lighting, lighter or other is shorting out (possibly due to a break in wire insulation).

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Re: Any idea why #3 fuse keeps blowing
#6
GREG WALSH
Cocoa, FL, USA   USA
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I had the same thing happen on my 74. There was some under dash wires on the passenger side that were hanging kind of low so I thought I'd tie wrap them up a little neater. Then the fuel pump, tach and gas gauge quit working and the brake light kept blowing the fuse. I wiggled the wire harness where it went through to under the bonnet and everything started working again but the brake lights were dim. I added an extra ground strap by the left motor mount and now all is good. Hope this helps. Greg.

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Re: Any idea why #3 fuse keeps blowing
#7
chris Avatar
chris Chris Roop (RIP)
Pendleton, OR, USA   USA
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Lee, that was my first thought, but I haven't blown fuses with that. You have??

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Re: Any idea why #3 fuse keeps blowing
#8
DSVW Dennis S
Ellicott city, MD, USA   USA
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1972 MG MGB GT
Sorry. My car is a 1972 MGB GT

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Re: Any idea why #3 fuse keeps blowing
#9
lgorg Avatar
lgorg Larry Gorg
Renton, WA, USA   USA
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1966 MG MGB "Robbie"
Ok, you will have a bit of work to do. Since you state your car is a 72, you have your choice of diagrams to choose from. I count 5 iterations, but you should be able to figure out which wiring diagram belongs to your car. Diagram 11, 12, 13, 14 & 15 all state they are for a 72 and I can't tell which one belongs to your car. Diagram 11 is on page 12. I would check to see what wire comes out of the 3rd fuse down. That will be the first step in determining which diagram you need to use. The wire color exiting the fuse will be either a green or purple wire. If its a green wire, it will be easy to check as there are only a few connections. If its purple, its the always hot fused wire.

http://www.advanceautowire.com/mgb.pdf

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Re: Any idea why #3 fuse keeps blowing
#10
DSVW Dennis S
Ellicott city, MD, USA   USA
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1972 MG MGB GT
Thanks. They are green wires.

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Re: Any idea why #3 fuse keeps blowing
#11
barry s Avatar
barry s Barry Stoll
Alexandria, VA, USA   USA
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1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
How are you counting fuse #? What is # of brown feed from the starter?

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Re: Any idea why #3 fuse keeps blowing
#12
DSVW Dennis S
Ellicott city, MD, USA   USA
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1972 MG MGB GT
As I stand over the fuse box it is the third fuse down from the top. on the left side as I stand above the fuse box there are two leads. one lead has one green wire and the other lead has two green wires connected into one fitting. The other side of the Box has one lone white wire. thanks for your help.

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Re: Any idea why #3 fuse keeps blowing
#13
barry s Avatar
barry s Barry Stoll
Alexandria, VA, USA   USA
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1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
Sorry. Description that I offerred in post #5 is wrong. My addled brain 'mis-thought'. That 3rd fuse is the green circuit. As it feeds both the tach and other gauges, your description of outages makes perfect sense. That means that there are tons of opportunities for a short.

I'd start the search with removal of one of the two females on the left (fused) side of #3. That should eliminate at least one side ot the green circuit as the culprit. From there on you'll need to proceed from the fuse box looking for connector to narrow the search.

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Re: Any idea why #3 fuse keeps blowing
#14
steve78b Avatar
steve78b Gold Member Stephen Brockwell
Elgin, OK, USA   USA
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1978 MG MGB "Lilith"
I had almost the same problem in my 78. Turns out I had the wiring reversed on my clock and kept blowing fuzes.

I had to start at the fuze and trace wires to each connector and put a small piece of white tape on the checked and cleared wires.

Slow and steady, you'll find it.

The autowire diagrams are invaluable.


HIF4 carbs
45D distributor with points
Non-overdrive

Steve B

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Re: Any idea why #3 fuse keeps blowing
#15
Skipper34 Avatar
Skipper34 Lee Baker
Napanee, ON, Canada   CAN
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I had the same problem. That fuse in my 79 MGB powers the electric cooling fan as well as the guages you mentioned. Apparently the bearing was bad and drawing too much current. I took that fan off line and had a new high tech fan installed directly on the radiator. No problems since and cooling has improved even in 90 degree weather.
Just in case I still carry extra fuses. I was replacing #3 a lot at one point.

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