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MG MGA - Strange Electrical Lighting Fault

I recently followed Barney's instructions to totally separate my indicator lighting system from the braking light system. This included totally by-passing the Indicator relay unit which is now redundant. All has been working fine until yesterday when, during indicating, I lost all brake lights, the indicators and my electronic tacho. Fuse A3 to A4 blown I assumed, but no, it is intact. All my main lighting is still functioning fine. My first visual check shows no obvious loose (ground) wires etc. Looks like a job with the meter unless someone can come up an obvious answer.

Steve
Steve Gyles

Located the problem quite quickly. I noticed the ignition warning light was also not working. I wiggled the key in the ignition and it all came back to life intermittently. I have not yet checked if it's a loose wire from the switch or a poor internal contact. It's an original switch. Not something I have taken apart before. Did I read somewhere on this BBS that reproduction switches are not that good?

Steve
Steve Gyles

Steve, my repro ign switch seems to be ok, it has been on the car about 8 years now and I have had no problems with it.
Like all the repro switches I have seen, it has spade connectors instead of the original screww terminals. (I think it is probably the same as an early MGB switch)

To reduce the load on the switch I have bypassed it for my 2-speed windscreen wipers, the twin electric cooling fans and my new combined headlamp dip/flasher switch.

Colyn
c firth

The 1/4-inch Lucar terminals are really bad when it comes to passing 20 amps through the input terminal. For this application, if you want to use the ignition switch with Lucar terminals, it is best to install a barrier strip to hard wire the headlamp circuit to bypass the ignition switch. See here: http://mgaguru.com/mgtech/electric/et124.htm

The "U" shape Lucar terminals on the ignition switch sometimes have the rivet come loose. See here: http://mgaguru.com/mgtech/electric/pics2/igsw17.jpg
It can be repaired. See here: http://mgaguru.com/mgtech/electric/et126.htm
barneymg

Thanks for the info Barney. I have just got the switch off. The terminal rivets are ok. The terminals also look reasonable, just generally a bit tarnished. However, the Brown and blue wires, plus the white wire look a bit heat hardened where they are crimped to the female spades and some of the cable insulation appears to have melted back very slightly. The switch is functioning ok on the meter.

A more thorough inspection tomorrow and a decision required on whether to replace the switch.

Steve
Steve Gyles

Barneys reply reminded me that I had also rewired the lighting circuit by fitting a new supply direct from the starter switch with its own dedicated in-line fuse.
My intention being to reduce the load through the ign sw and its lucar spade connectors as well as to protect the wiring.
His idea of a Bus bar is a great one and it is on my to-do list.
Colyn
c firth

Steve

Do you have a lot of keys on your keyring?
Dave O'Neill 2

Use a relay to take the load off your ignition switch. Ignition switch operates relay (really low current), fused power supply via relay contact powers ignition switched circuits, simple!
Lindsay Sampford

You have used the "r" word Lindsay, I seem to recall that Barney is not big fan of relays and so you are now probably in danger of being excommunicated from MGA Guru! :-)
(it would work though Lindsay, a relay would take all the load of the switch)
Colyn

PS Please be gentle with him Barney! :-)
c firth

I have just followed Barney's guidelines and dismantled the switch. Very good condition inside with no arcing evidence etc. In fact the contacts look totally unworn and show bright metal. I would venture to suggest that these contacts are more solid and better engineered than the starter switch contacts that I have previously taken apart. One of the spade terminal rivets is very marginally loose but I don't think enough to cause electrical issues but I will put the meter across and wiggle the joint to see what happens. A slight tap with a centre punch should tighten it. I am inclined to think that my issues revolve around the female connectors on the wires, so off now into the garage to inspect more closely and sort.

Dan, only two keys (ignition and boot) plus fob and garage door zapper. Total weight 51g.

Steve
Steve Gyles

Oh well. it's a new switch anyway. The body flange broke off when I started to re-rivet. Just ordered a new switch body from Bob West. He asked if original or Lucar style as both are available as repros. He said to avoid the original style like the plague as they are very poorly made and have been causing them endless trouble.

Steve
Steve Gyles

Happy to report that a new ignition switch body and new terminals on the wires has cured the issue. All is good with the world.

Steve
Steve Gyles

.....and finally today I fitted a new flasher unit. The result is a significant improvement in the flasher interval and the lights are much brighter, especially the jewel. Mind you, one of the female spades pulled straight off its wire during transfer so I may also have also been suffering some high resistance! I then took the old unit apart and found a single straight strand of very fine wire, about an inch or so long just lying among electrics. I am not sure if it ever had a function or was a 'foreign object' left lying in there during manufacture.

Steve
Steve Gyles

It's my understanding that the problem is not current through the switch, rather current through the terminals. The MG factory used the ignition switch as a terminal strip of sorts, which worked fine when the switch had screw terminals. The Lucar terminals are not as good at passing current as ring terminals held down tightly with a screw, so they heat up and cause the switch to eventually fail, even though the current causing the problem isn't actually switched by the ignition switch.

So, you don't need a relay at all, just an additional terminal strip to pass the load, as Barney suggests.

-Del
D Rawlins

This thread was discussed between 22/09/2015 and 04/10/2015

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