MGB & GT Forum

Little more than two weeks ago I blabbed that I would post about repairing the headlight rocker switch in my 71 GT. Partly, I've been really busy, partly I wanted to see if my repair held up. And it has. I drive my GT at least 6 days out of 7 every week, and I deliberately turn my lights on day and night for safety. I'll do the best I can with the descriptions--I couldn't bring myself to take it apart to do photos. First a couple pre-existing conditions:
1. The instrument light dimmer switch appeared useless--no instrument lights
2. as described elsewhere, my main/flash/directional switch fell apart, and to get any headlights at all I had to rubber band the stalk back into the "flash" position, although this never resulted in my high beam indicator coming on

Under these conditions, my parking lights ceased to work. Still had headlights with the stalk switch jerry-rigged, but no front marker, no tail lights. I pulled the rocker switch, opened it, and got my eyes opened.

The switch is very simple, very sturdy. The rocker comes off very easily. The ball bearing and spring were pretty greasy, and so didn't pop off across the bench. There is an actuator at the bottom of the housing that does simply rock, closing first the parking lights circuit, then closing the headlights circuit and still keeping closed the parking lights circuit, all under pressure from the rocker you press on. The key to both these circuits is the profiles on the underside of the actuator--the molded-in shapes that press the four separate contacts together that complete the park and head circuits. I found both pairs of contacts sound and clean, and they tested fine when manually closed. When I turned over the actuator, this is what I found:

The head side of the actuator (right side as you look down into the switch, left side once you pull the actuator and turn it over) is shaped like a crooked index finger, angled as if to try a scratch-and-sniff in a magazine. This looked ok on my switch, and the head side tested good with the switch assembled. The park side (right side when actuator is pulled and turned over), is supposed to be shaped like your thumb, upturned in an exaggerated thumbs-up, in particular the middle joint. The park side is supposed to be radiused, so that it closes the contacts in the first rocker position and they stay closed in the second, park+head position. This side of my actuator was worn flat, and showed some signs of melting, and then I knew why the park side was dead when tested with the switch assembled.

I don't know how the combination of age, use, and the electrical faults 1 and 2 above all added up to the erosion of the park side of the actuator, but this is what I did:

1. I cleaned the actuator with grease remover
2. I filed flat the worn surface of the actuator park side
3. cleaned it again with degreaser
4. took out every spare switch I had, lined them up on the bench, and.......looked carefully

Finally I settled on an old Hella switch that had an insulated, round actuator shaft, and then....cut it to pieces. First in half, then in quarters, then sliced down to a radiused fragment that fit the profile of the Lucas park actuator, with what seemed like enough overall lift--like the lobe on a cam--to close the park contacts in both rocker positions. BUT, it was still just a guess. I used super cyanoacrylate glue to attach this tiny lobe to the park side of the actuator, let it set, then put it all back together. FYI I used 2P10 glue, not the "insane" supermarket brand.

And damn it worked--perfectly. It's probably been thru about 200 cycles--not many, not by a long shot. But the "feel" of the switch is excellent. Some mornings I turn on the parks and turn them off a couple times, then go all the way to headlights, then back to parks...you get the idea. I play with the switch--gently, as if it was an electrical device, not mashing it.

After this, I replaced my main/dip/flash/directional switch, and wired a 10 ohm resistor across the contacts of my dash light rheostat, both with positive results.

I believe repairing an eroded head side of the actuator would be trickier, but possible.

Yes, they can be repaired. Good job.

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"It is a mistake to try to look too far ahead. The chain of destiny can only be grasped one link at a time."
Sir Winston Churchill
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"It all starts in your mind's eye, then it goes to your heart
and finally to your very soul."
G.S.George PHD

I have repaired a number of switches. I find the most worrisome part of the project revolves around the brittleness of the old plastic housings. If I can get them apart without breaking off tabs or "ears," I can usually clean them up pretty fast. I use fine emory paper and/or a pencil eraser to burnish the contacts, apply a tiny little drop of an anti-corrosive like Cramolin, and carefully snap them back together, Broken plastic is dealt with by using a spare amount of model airplane cement, knowing as I do that it is probably the last time I'll be taking that particular switch apart.

Also, as the OP noted, "exercising" the switch by using it is a well-know bench tech's remedy.

D.

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Douglas Tourtelot
Seattle, WA

"Every education has a tuition"