MGB-GT Reproduction light switch

[Crazyman60]

Just got started tinkering with my newly acquired ‘72 GT. I began replacing different switches such as the hazard switch blower switch and lastly the light switch. I needed to get my state inspection so I that I can drive it. Everything inside is beginning to coming alive again, until tonight. I pushed the light to turn headlights off and switch broke, it would not move. I took the switch out and it had melted. Any ideas?

 

[Grantura_MKI]

Would check the fuse values and for a direct short.

 

[bobhustead]

Check also the wiring diagram to see if there is a relay someone might have bypassed thus passing the whole load thru a switch not designed to handle it.
Bob

 

[Crazyman60]

Thanks. There no telling how many hands have been on this car in the past 50 years. The original switch was broken internally but there was any sign shorting. The bottom of the steering column and behind the console, I found lots of spiced wires.

 

[bobhustead]

I looked at Moss catalog and find no mention of a light relay. I say you have a short that you need to track down.
Bob

 

[Crazyman60]

Until a day ago the lights were being turned on for short periods. I got the safety inspection done on it yesterday and I have been driving everywhere with the lights on. One thing that I forgot to mention, The tail lamps stopped working right before leaving for the inspection. Lots of fooling around back there by previous owner’s. The headlamps where working then.

 

[DrEntropy]

IMHO, a "short" someplace in the wiring would result in the dreaded Smoke Release. What is more likely is the switch overheated due to high resistance somewhere in the lighting circuit. Better to find and clean/refurb ALL ground points in the light circuit. It wouldn't hurt to add a relay and redundant ground wiring either. A ground wire for the rear is using the license tag fastener inside the car as a ground, that one can be a hidden issue. Lights draw a fairly heavy load compared to most other things, why BMC/Leyland didn't put relays in the lighting run is beyond me.

And don't get me started about aftermarket wiring and controls...

 

[Mickey Richaud]

And you'll need a good, easy to read wiring diagram: www.advanceautowire.com/mgb.pdf

Just scroll down to your year.

 

[Grantura_MKI]

I have done many plastic English motors and never had all of the issues that folks experience with earths?
All English wiring codes are the same. Really no need for a diagram once you memorize the colours.

 

[Crazyman60]

IMHO, a "short" someplace in the wiring would result in the dreaded Smoke Release. What is more likely is the switch overheated due to high resistance somewhere in the lighting circuit. Better to find and clean/refurb ALL ground points in the light circuit. It wouldn't hurt to add a relay and redundant ground wiring either. A ground wire for the rear is using the license tag fastener inside the car as a ground, that one can be a hidden issue. Lights draw a fairly heavy load compared to most other things, why BMC/Leyland didn't put relays in the lighting run is beyond me.

And don't get me started about aftermarket wiring and controls...

 

[Crazyman60]

I just bought relays from Moss and I am checking wires, and I must say that I am learning the colors of the wiring, the hard way at times.
When I replaced the original headlight switch it was because it had come apart internally. There were were no signs of overheating on the wires or switch itself. The replacement literally melted where the spades are. I will be checking the grounds. Thanks to everyone for your help and insight.

 

[Grantura_MKI]

Relays are good as long as they are wired correctly.
They are to take the load away from the switch. Napa sells relays if you need them quicker.

 

[mezy]

I've had aftermarket switches in the past. Mostly they are pretty crap compared to an original switch. The parts in as idevthe switch are thinner and contacts are not as good. These arc and Couse the brass bits to heat up and melt the plastic. If you have no alternative use a relay to remove the load from these switches

 

[YakkoWarner]

I know Moss sells a relay kit that you can use to take most of the current load away from the switch. There are no lighting relays from the factory, and with all the lamps functioning there is around 15 amps of current going thru that switch (and that can certainly generate enough heat to melt the plastic).

Going to LED bulbs would also reduce the current draw dramatically.