Is your MGF blowing fuse 7 30amp constantly? This 30 amp fuse is located in the under bonnet fuse block which house 7 fuses. In the owners the fuse is described as fuse number 7. However, using various MGF wiring diagrams, this seems to be described as fuse 1. Either way its easy to identify by physical position and the fact it is 30 amp.
From some personal experience, and some shared experience, so far there are a couple of possibilities identified. These are described with symptoms an solutions for these. Hopefully these are helpful to getting a problem resolution.
The impact of this fuse blowing is that if the car is turned off, it will not start again from the key. You may be able to bump start the car but the starter motor will not work. The car will continue to run with the fuse blown.
What Does Fuse 7 Protect? When Fuse 7 Is Also Fuse 1 #
Using the service manuals to inspect the wiring diagrams it seems this 30 amp fuse sends power to the engine controls relay box. Inside the box are 4 relays. Two of these relays are powered by fuse 1 (aka fuse 7 in the owners manual) in under the bonnet (hood) fuse block.
Symptom: Fuse Blows Immediately After Starting #
This is an experience that was diagnosed by a friend. The car would start fine and immediately after starting the fuse would blow.
Cause/Solution – Replace O2 Sensor #
One of the relays powered the starter signal wire, this circuit appears to be OK as the vehicle is able to crank and the fuse doesn’t blow until after the vehicle has started. However, the other relay powers the O2 heater circuit.
You can locate the O2 (lambda) sensor connector just above the gearbox on a mark 1 car. Check the wiring of the O2 sensor for chaffing. Also check the car side of the connector to the O2 sensor for chaffing. If you find nothing that is causing a short, disconnect the O2 sensor from the main harness.
Leave the O2 sensor disconnected and install a new fuse into under hood fuse panel. If the car starts and doesn’t blow the fuse then the O2 sensor wiring or sensor itself is the cause. Either replace the sensor (if replacing use a genuine Bosch unit to avoid future issues) or conduct testing to repair the problem.
Symptom: Fuse Doesn’t Blow Immediately. Blows When Car Is Driven #
This was something that I experienced first hand. I could start the car multiple times and even left the car to idle for 10 mins and the fuse didn’t blow. However, driving the car seemed to cause the fuse to blow, even after a short drive of 2-3 miles. The car would keep running but if you turn off the ignition, the car wouldn’t start from the key, as the fuse was blown. Similar to the first example but different.
Cause/Solution – Mitigate Chaffing Wiring #
As with the above example, you will want to check the O2 sensor for a chaffed wire. It could be this causing the issue vs. the actual O2 sensor failing as was the case above. The same disconnecting the O2 sensor can assist in diagnosis.
The fuse 1 feed also powers a relay involved in the starter. So it’s also worth checking the wiring in and around the starter for chaffing wiring.
In my situation it seems the issue was with a chaffing wire going into (or out of) the Engine Module Relay Management system. This sits behind the main ECU box. What I found was that the wires entering from the left side (looking to the front of the car) were rubbing on the metal frame of the ECU mount. A closer examination reveals that the outer sheathing of a white with pink wire was damaged. Not much damage but apparently enough to cause a short. I added some electrical tape to the wire bundle. I also added an insulating pad to the frame itself.
Hopefully, if you are dealing with an MGF blowing fuse 7 30amp constantly, one of these solutions will also work for you!
Other Materials #
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