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MG MGA - Sorry, yet another fuel gauge problem

At the end of last driving season I had the fuel gauge professionally rebuilt.

I re-installed it and it worked quite nicely.

After having done so I had trouble with the car shorting out and stopping. After a quick search under the dash I found that one of wires to the ignition switch was loose. I tightened that wire and all seemed well except now the fuel gauge doesn't work.

Can you take pity on a man and help me sort it out.

Be kind, I am not clever with electric system, but I do have a meter and have been able to stumble through with the basics.

Thanks as always,

Tysen
Tysen McCarthy

Follow the directions given by Barney Gaylord!!!
Dirk
Dirk Van Ussel

Yes, Barney's stuff is great....I just struggle through the electrical. Mechanical I'm very good with.

Anyway I think I've found the problem. The top fuse is blown. (interestingly enough the car still starts, is it supposed to?)

I went to Barney's page and it seems that I have the wrong fuses installed.

The top one is stamped SFE20

The bottom one (still intact) is AGC20

Can the right fuses be purchased at the auto store, or is this a Moss purchase?

Tysen
Tysen McCarthy

Ok, I've read Barney's page about fuses and searched the archive and I'm still confused.

Barney's page says its a 17/35 fuse on the top, which I'm gathering is a Moss product. In one of the archive posts he suggest to just use a simple 20 amp.

The bottom horn fuse is still a mystery to me. Some of the posts seem to suggest a 50 amp fuse. Any suggestions would be welcome.

Thanks
Tysen McCarthy

Tysen,

Assuming you have a standard car use 35amp fuses for both positions. If you have to order them get four and keep two of them in the 'spare' positions in the fuse box.

The starter current does not pass through either of the two fuses as the starter typically draws 100-150 amps from the battery!....................Mike
Mike Moore

Mike,

Thanks for the response. Just to add to the confusion, from the archives I'm gathering there is a difference in the way fuses are rated between the UK and the US!

I'm not sure about the specifics of the distinction. I'm wondering what impact that may or may not have on your recommendation.

Tysen
Tysen McCarthy

Tysen
If it isn't broken why fix it
If your bottom fuse is a 20 and going ok leave it alone
The only time you would need a bigger one there would be if adding extra horns
I'd replace your blown top 20 amp fuse with another 20 and see if that fixes it
There is the strong possibility that you might have shorted something while working under the dash and all you need is a new fuse and all will be well
If the fuse re-blows instantly, then you will know that something needs looking at on that circuit- but just try a fuse first up
I'd be staying away from 50 amp fuses though--things can get a bit too hot before a 50 will blow

The 17/35 amp fuse mentioned by Barney is a 17 amp fuse but will take 35 amps for a VERY short time

Example
A pair of 100 watt high beams will draw a constant
approx 14-17 amps depending on voltage supply but when you first flick them on they can got to 30 or so for a split second until the globe lights up
In this case a good quality 20 amp fuse can hack this spike ok but some won't
A fuse rated as above ( 17/35 ) shows that the manufacturer guarantees that it will run at 17 amps and take spikes of 35 amps
Most fuses will do this, it is just a case of they have put it in writing in a different way--maybe law in whichever country--or simply explaining the limits of the particular fuse
A 20 will cover you ok
willy
William Revit

If the fuse had gone it should be obvious as most electrical items in the car won't work (excluding lights and horn).
Lucas glass fuses are rated at their "blow" rating (in the uk at least) so safe running is about 50/60% of that (it isn't a precise science) whereas modern fuses are rated at their running current (and will fail at around twice the current). Therefore you can't replace the old Lucas fuses with modern types of the same marked amperage.
Graeme Williams

This thread was discussed between 18/02/2017 and 21/02/2017

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