Lost power on motorway. Ignition permanent live fault

[thecyrusvirus]

Hi Everyone

I went off this morning and did some work at my MD's house. Then left and hit the motorway. All of a sudden I felt the van start slowing down, wipers stopped wiping. All the dashboard lights went off.

Turning the ignition key from off to on made no difference. The oil light would sometimes come on for a fraction of a second but nothing else.

I thought at first it was down to my immobiliser so I bypassed it (waste of half an hour!)

No multimeter in the van so I whipped out a spare bulb and some wire to test for live at the ignition red wire. (bulb lit up)

Spent another 30 mins scratching my head,testing various wires. bulk lighting up on all of the tested wires.

In the end I put the bulb across the battery terminals and it was much brighter than when on the ignition wire. So I guessed at voltage drop at the ignition wire. Ran a temporary wire from the battery positive to the ignition live and we had lift off.

Now home and tested the ignition live (just under 6v) starter battery 12.9v.

So, I am guessing the wire is just old and degraded. Just weird for it to fail on the motorway like that.

I can see that it runs out through the bottom of the battery box, but from there where does it go and what is its route to the ignition switch.

It looks like it is about 6mm squared and is more of a faded red/ pink than red but I am sure you all know which wire I mean.

If I am going to replace this wire, what sort of length will I need?

[bigherb]

It goes from the battery across the cross member above the tank to the left chassis rail then follows the rail to the front then goes up by the rad and through the bulkhead to the fuse box. I would check where it connects to the fusebox first not unknown for the connection to have overheated.
Yes it is 6mm cable

[thecyrusvirus]

Cheers bigherb.

I shall take a look this evening when I have finished work.

[thecyrusvirus]

Just popped out for 5 minutes to check it.

12.7v at the incoming spade terminal on the back of the fusebox.

12.7v halfway along the feed to the ignition and 12.6v at the ignition! (not the 5.8/ 5.9v I was getting earlier)

Could the cable behave differently under load? i.e. could the resistance be increasing when it gets hot and thus resulting in the voltage drop behaviour I had? Bearing in mind the less than 6v reading I had was an hour after stopping the engine

Is it worth just changing the entire run of that cable for peace of mind?

[bigherb]

Could the cable behave differently under load? i.e. could the resistance be increasing when it gets hot and thus resulting in the voltage drop behaviour I had?

Yes always check voltage when under load.