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MG MGA - Brake Lights

Last week I replaced a broken dash headlight switch, got all the screw connections proper and tight, everything works OK except that now my brake lights don't work! They're not routed through that switch anyway, right...the problem must be somewhere else?
Jim P

I would start at the hydraulic pressure switch and work my way through the system with a multimeter.

Cli8ve
Clive Skelhorn

Jim - Do you knowforsure that the brake lights were working before you replaced the headlight switch? You are correct, the brake lights are not associated with the headlight switch, but if you were anywhere around the fuse block you may have knocked loose one of the green wires. Power for the brake lights is switched 12 volts on a green wire to the brake light switch. It leaves the switch on a green/purple wire to the brake lights. WIth the ignition switch on, jumper across the terminals of the brake light switch with a short piece of wire and see if the brake lights come on. If they do come on, then the brake light switch is bad, if they don't come on either the voltage is being lost between the switch and the light sockets or there is a bad ground to the sockets. Good luck - Dave
David DuBois

My bet is a bad bullet connector.

For the 1600 start here: http://mgaguru.com/mgtech/electric/circ_f3.htm
Green from fuse to brake switch.
Green/Purple from switch to lamps.
Black from lamps to ground.
Find the 2-way connector "EC" in the engine compartment near the starter switch.
The 3-way connector Green/Purple and the 6-way connector Black are both aft of the RR wheel.
Ground is (originally) on the frame near the fuel tank sender unit.

The 1500 is a bit trickier:
http://mgaguru.com/mgtech/electric/circ_f2.htm
Green from fuse to brake switch.
Green/Purple from switch to relay.
White/Purple from relay to LR lamp.
White/Brown from relay to RR lamp.
Black from lamps to ground.
Find four 2-way connectors "EC" in the engine ompartment near the starter switch.
Find 2-way connectors white/purple and white/brown, and 4-way connector black aft of the RR wheel.
Ground is (originally) on the frame near the fuel tank sender unit.
Barney Gaylord

Jim

Is it a brand new switch? Could it be faulty? The reason I ask is that I bought a new pull/twist/pull switch to run my wipers at the first pull and the wipers+washers at the second pull. By and large it work ok, but occasionally I get random squirts of washer fluid with all switched off (once when my passenger was just getting in - quite amusing actually) and sometimes the wipers just stop. The contact mechanism inside the switch seems quite delicate. They don't make them like they used to.

Steve
Steve Gyles

Yup Barney was right, a bad connector. I jiggled the wire harness and sure enough traced the problem down to a loose wire and bullet connector.

Now I discovered ANOTHER problem...melted wire in the middle of the harness. It's the wire that feeds the dash lights and parking lights. I suspect that the halogen bulbs that I installed from LBCco are to blame (I switched speedometer, tachometer, oil/water gauge and all exterior bulbs to halogen). It makes a huge difference in readability at night (now I can actually SEE the gauges) and the front and rear parking/tailights are substantialy brighter but at what cost? Anybody else have this issue? Any fix other than changing back to "dim" tungsten bulbs?

thanks in advance.
Jim P

Jim - If the burned wire hasn'e damaged any of the other wires to the point where there is a chance of any of them shorting together, you could disconnect the wire feeding the dash lights (and to the parking lights if the wire going to them is also overheated) at both ends and piggy-back a new, heavier gauge wire onthe harness to the original points. I would recommend a AWG 14 wire or possibly even AWG 12 (although the latter might be overkill). Good luck - Dave
David DuBois

Jim, check the wattage of the new bulbs, if they are the same as the standard bulb they will have no adverse affect on the wiring. In most cases the halogen bulbs are the same wattage, there design is what results in the brighter light.
John H

Jim, I mentioned in another post that I'd just done the wiring to the front lights. The reason was that the same wire (red) had melted into the almost new harness. This was caused by some brand new front turn signal assemblies I'd installed. I bought them a couple of years ago before I even had an MGA. The wires in the sockets had never been crimped correctly and fell right out, shorting to the metal case. Of course you can't see this unless you pull the rubber boot off the shell of the fixture.

I replaced the front, main, and dash harnesses and fused those light circuits, along with the headlamp circuit.

So, like John says, I would not suspect the halogen bulbs to be the first culprit. Better check your fixtures and make sure you don't have one shorted.

My first thought was the tag lamp; that one looks like a short waiting to happen. I did some preemptive insulation on that wiring.
Wray

Wray you may have something here. My LICENSE PLATE lamp is always intermittent, even though I have cleaned all connections and the ground, it never seems to maintain a "clean" ground. If I squeeze the chrome housing of the lamp, the light gets brighter. this may indeed be the culprit...
Jim P

Jim, won't hurt to give a good visual inspection. As I found out, the red circuit will indeed carry a full 20 amps to ground as it happily melts into the rest of the harness....

The big insult was that it was brand new lamp assemblies. And the harness that they ruined looked to be brand new, too. My first indication of a problem was that my tailights weren't on and the shaft on the headlight switch was so hot it burnt the crap out of my finger.
Wray Lemke

This thread was discussed between 22/01/2006 and 25/01/2006

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