melting fuses

[hot-growler]

Hi, apologies as this is not TR6 related. My 6 is behaving well thankfully. Problem is  Mk3 Spitfire with a 30A drain when sidelights are on fuses either blow or worryingly start to  smoke. I casn hear the battery bubbling away as if it is not happy. Happened to leave the lights on inadvertantly while checking instrument warning lights. Checked my other Spitfire and it only drains 3A when sidelights are on and about 12A on full beam. Lights standard not uprated. 

Any ideas? 

Many thanks, Stephen Brady.

[DIYBOSSCAT]

Hi Stephen,

looks like a short down to earth on the loom somewhere. Can you isolate the side light circuit front/back anywhere by unplugging the relevant wire, then trying a new fuse again. If it's ok then the fault is after that.

Vince.

[BlueTR3A-5EKT]

Have you recently changed any bulbs?   The rear lamp bulb holders bend back when you insert the bulb causing a short to earth.  Same arrangement on side screen TR.

Peter W

[RobH]

DO NOT replace the fuses and do it again Stephen. Your wiring loom may well already be damaged if the fuse smoked but did not blow. The wires can overheat and melt their insulation - this may not be visible as it will happen where the wires are wrapped together where the heat will be trapped. The light switch will not like it either.

Smoking fuses means you may be using the wrong ones and the fuse holder may well be damaged. The wiring diagram I have shows the fuse should be 17A. You say the fuse was replaced but did not blow with a 30A discharge - an automotive 17A fuse will blow at 17A, but a standard fuse with the same rating will pass that current indefinitely.

I suggest you disconnect the lighting feed from the fusebox and check for a short to earth with an ohm-meter after first removing all the sidelamp bulbs. If there is no short then replace the bulbs one by one until the short reappears. Don't re-connect the lights until you are sure you have found and rectified the fault. Check the loom thoroughly where possible, for any visible signs of overheating. If you find any then consider whether it would be safest to replace it. 

 

Edited May 10, 2020 by RobH

[hot-growler]

not changed anything recently just a stereo and attempting to get thehorn  push to work.  I probably haven't had the lights on for months. Opened up the rear lights and looked a bit of a mess. There were about 6 scotchloks on the loom. Think it's had a towbar on in it's lifetime. Unscrewed the fuse box and seemed to make a difference when I fiddled with it.

[hot-growler]

Ooh. OSF side lamp holder was badly corroded and bulb looks like it was the cause of the short. Think that is where the problem lies. Thankfully wiring looks ok. Will purchase a replacement unit and re assess. Must admit I have never stripped them down since purchasing. 

I will check all my other cars as they are all 30 years old or older.

Thanks.

Edited May 10, 2020 by hot-growler
Could this be it?

[hot-growler]

Could this be the cause? 

 

[Mike C]

3 hours ago, hot-growler said:

Could this be the cause? 

 

Insulate the bulb holder from the body and see if the 30A drain has gone.

[hot-growler]

Number plate light. Can see the melted wiring. Cheap after market rubbish live fallen off inside. Need to replace that part of the loom.