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MG Midget and Sprite Technical - Turn Key, Blow Fuse

After leaving the ignition on overnite, I had a fire in the tach. I replaced the tach and the coil which was fried

It seems I am blowing fuse #2 White to green wires as soon as I turn the ignition key

the car runs fine, but withiut tach fuel guage and possibly a few other lights

Any suggestions of where to start hunting?

Phil
Phil Burke

Burnt ignition wire inside the harnness is my fear, its grounding out or making contact with another damaged wire,

Run a new wire to replace it out and make sure the battry is disconnected when not in use and keep a fire extingisher close by...harbor freight has those cut off switches with the red key, and radio shack has project boxes you can attach the switch to and re route your batt cables .... Lo easier then wrenching the batt lead off and on

Prop
Prop

Phil. How many connections are coming off the back of the fuse that powers the green wire circuit? Normally, on the MGB, at least two. When I had this problem, I picked up some of those in line fuse holders, installed a ten amp fuse in each, and connected them to the power output on the fuse box, then to the input wires that normally connect to the fuse box. When one of the ten amp fuses blew, to told me which green wire circuit the problem was on. With a wiring diagram in hand, one then needs to check all of the wires in that segment of the circuits to find out where the problem is.

I would not be surprised, as you get into the wiring bundles, to find that the wire which is shorting out has damaged one or more of the other wires in the bundle.

Les
Les Bengtson

Les,
I split the two greens at the fuse box and I have isolated to; the fuse does not blow when the green wire is disconnected from the tack.
Also the brake light and fuel guage circuit is off.
Could I have gotten a bad tach?
Phil
Phil Burke

Phil. Most probably, when the tach burned up, some of the wires going to it overheated also. The one time I did something like this, there were several burned wires, all of the wiring bundles containing them had to be opened up, and all of the wires examined, replaced as necessary, then rebundled. (I used cable ties and the blue 3M electrical tape.)

A simple job, but one which is time consuming, not great fun, and boring. But, I have never turned on the ignition switch, when trouble shooting, without removing the wire from the coil to the dizzy since then. Hard lessons are a great teacher.

Good luck with the trouble shooting.

Les
Les Bengtson

Open up wire bundles
Just as I feared
Thanks, Phil
Phil Burke

Duh
When I put the new tach in, I connected the 2 green wire to the center spade terminal on the tach.
A CHASSIS GROUND
No wonder my green fuse blew so quick
An easy find and fix once I attcked the problem 1 circuit at a time
Thanks, Phil
Phil Burke

Phil. Glad you got it sorted so easily. But, keep an eye on the wires that got hot when the ignition switch was left on. When I did it, I found several wires with melted insulation, offering a potential for future trouble.

Les
Les Bengtson

This thread was discussed on 05/07/2011

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