Fuses

[vauxhallbitz]

Took the Viva for it's MOT today and on the way the ignition light came on. I stopped the car and restarted it but noticed that the indicators and gauges were not working.
It appears that a 50 amp fuse has blown, my question is, where can you get this type of fuse as the only ones my local garage has are different size and shape.
Any thoughts on why it blew also appreciated........

[1972nail]

I have a supply of the correct brand new 35 A fuses. The 50 A ones are exceedingly rare. You really need to find out what caused a short big enough to blow the fuse in the first place.

Vauxhall originally only fitted 35 A fuses but found that the HRW and 2 speed fan etc drew enough current to prematurely 'age' the 35A fuse and it would eventually give up, the 'fix' was to fit a 50 A.

[vauxhallbitz]

Thanks for that, I am going to try normal glass fuses until I get to the bottom of the problem and then try to find the correct one. If I can't get one I will come back to you for a 35amp one.
Have no idea what has happened everything was fine until it went for the MOT today.
The trials and tribulation of classic car ownership........

[jpsmit]

Not exactly sure how the HC compared to the GT in terms of wiring, though considering the era, they can't be far off. I have been working on my wire harness for a couple of weeks now and the notion of a 50 amp fuse terrifies me! Those wires mostly seem undersized already.

Every wire harness I have (and I think I have 4) had the wire from the alternator to the ammeter burned and frayed at exactly the same spot. Others on the board assure me that it is where the harness is clipped to the oil pan - the wire eventually wears through and grounds on the engine. Assuming there is some similar arrangement on yours, this would I think account for both the loss of charging ability (light goes on) and fuse blowing (grounding).

In terms of the fan etc, this would be a really good time to add a relay or two - they are easy and cheap insurance and will lower the draw on the whole harness.

[1972nail]

I think JP is on the right track. Check the alternator wire running below the front pulley on the engine.

[vauxhallbitz]

Thanks for that, I will need to check everything out but will bear that in mind.

I tried a new fuse in today and it blows the instant you put the ignition on.

[Fred Dukes]

Get your multi meter out and start measuring ohms from that fuse to earth - you should measure more than 0.5 ohms to not blow a 35A fuse so you have a dead short somewhere Check your wiring diagram see what connects to the fuse - sounds like agood start to physically examine the loome going around the sump to the alternator. We have prob got that particular loom up in the shed.

[vauxhallbitz]

It appears to cover the alternator, indicators, brake lights and the heater and not a lot else.

Will start to eliminate them one by one when I get the chance, the smart money appears to be on a short circuit diode in the alternator.

[1972nail]

Check the loom where it passes around the front of the sump just behind the front pulley. It's very common for the insulation to wear through there and cause the short you describe.

If it is OK then split a bit of appropriatly sized plastic tube and slip it over the wiring at that point as further protection.

[vauxhallbitz]

Fixed it at last!

Long story but I will post a picture of the offending item when I get the chance, took a lot of effort but was worth it.