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MG MGB Technical - Question involving smoke/fuse

I had a bit of smoke from my steering shroud area today. In looking around, I noticed a wire under the hood looked a bit odd.

This wire (with in-line fuse) runs from the white wire bullet connector to the tcsa switch used for my overdrive.

The odd bit is that the wire from bullet connnector to fuse (about 10 inches) looks melted (same for fuse). The fuse (35A) is not blown.

The other wires (after the in-line fuse) and around the white wire bullet connector look fine.

Does this mean the fault is just in that bit of wire that got too hot? Why would the fuse not blow?

Thanks in advance! David
David Steverson

the fuse rating is too high for that gauge wire I suspect. 35 amps is a good bit of power considering the factory alternator is only rated to about 36amps!
Robert

David
Is it possible that your inline fuse has or had an exposed live section that has touched the body or an earth. OR is it overloaded- you mention other wires after the fuse--where do they go to Willy
WilliamRevit

All MGB fuses are 17A rated, 35A blow, and they are there to protect the wiring. Unless the wire was particularly thin, or you have a 35A rated fuse instead of a 17A rated, I'd suspect something else.

Do you mean the TCSA switch? Or the fuel cut-off switch? The TCSA switch is on the gearbox, the TCSA solenoid is on the firewall, but only has a single yellow/red going to it.

The fuel cut-off switch has white wires, but like all white wires they are unfused and there is no factory in-line fuse in that area. However I do recommend fitting one to fuse the fuel pump (which along with the OD comes off the output of the cut-off switch) as three cars out of four I have or have worked on have had shorted pumps which has damaged the rear and main harnesses from pump faults.

The output side of the pump should have a single white coming off it going to a 4-way bullet connector, with two more wires in it, one to the rear harness (fuel pump) and one to the gearbox (overdrive). The input side of the cut-off switch should have two wires, one goes to the ignition switch and ignition relay, the other to the ignition warning light.

Given the smoke in the shroud, and the fact that only wire on one side of the fuse was damaged, Willy's thoughts of the fuse itself shorting to something (on its live side) is more likely. But it does all depend on exactly where the fuse is connected.
Paul Hunt

I obviously used the wrong fuse as somehow I thought 35A was the standard MGB fuse.

Yes, Paul I do mean the TCSA switch. The OD was all working good beforehand. I guess I need to trace back and look for the issue.

From reading the archives, it looks like it's fairly difficult to get to the TCSA switch. Oh joy...

David
David Steverson

David,

I had exactly the same problem a few weeks ago. It was at night and the headlights went out on high beam. Since it was dark, I was not sure where the smoke was coming from, but guessed the signal/hi/lo switch. When I stuck my finger in the hole to feel it, it was hot.

I bring this up because my OD switch is on the dash board, so there are other things than can release smoke from the steering shroud.

Charley
C R Huff

Don't forget to replace the Smoke.If you can find any.
Bruce-C

I have a few cans of BMC smoke that I found in the boot of an MG many years ago, so no worries there!
David Steverson

This thread was discussed between 03/05/2009 and 06/05/2009

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