DIY Landcruiser Third Brake Light Fix: $0.69

Today I helped a friend repair a malfunctioning third brake light on his 1996 Landcruiser FZJ80. He was alerted to the problem by the local police and his inspection is due this month so there was really no choice but to take care of it.


Searching around for a replacement, he discovered a new part was going to cost a whopping $200! Since there was nothing to lose and everything to gain by attempting a repair, we decided to give it a shot.

After using a voltmeter to verify power was getting the the board when the brake was depressed, we dismantled the brake unit (picture at upper left) and we saw that there was really nothing to it: a string of 76 low-cost red LEDs, a low-cost resistors, and a low-cost 5.1 volt zener diode. The point I am belaboring here is that $200 seems kind of steep for less than $10 worth of electronics and a plastic shell...

There was no obvious physical damage to the board, and nothing looked fried, although in retrospect the zener maybe had carbon residue on its leads (a sign that it burned up at some point). The voltmeter told us no juice was getting past the diode. Sure enough, temporarily shorting across it caused all the LEDs to light up. Looks like we found the problem.

NOTE: You may ask “Isn't shorting across things bad?” Answer: “Yes. Yes it is.” Don't do it unless you know what you are doing. Parts are there for a reason – you have been warned. In this case, the zener is probably there to act as a voltage suppressor to prevent power spikes from killing the red LEDs.

You may also ask “How do you know it was a zener diode?” Well, it was labeled it had the typical markings and form factor of a though-hole diode and was labeled E51. An Internet search narrowed down the choices to 5.1V zeners after that.

A quick drive to Radio Shack... Well, not so quick because traffic was ridiculous, and there were actually two Radio Shacks involved because the first stopped stocking “things that are useful” to make more room for “tasteless, shoddy, and ill-conceived stocking stuffers”. Ok... ok.... I am being unfair, but the love-child of Michael Bolton and Carrot Top that was working at the first one really pi... Ok... ok... calm down...

Anyway, the second Radio Shack had some low-current 5.1V zeners. They are $1.39 for a pack of 2. Feel free to get on their site and read the five unreasonably glowing reviews of these extremely standard parts. FWIW, the site also alleges they come with a hilarious 90-day parts and labor warranty for some reason.

We got back and soldered in the new one, making sure to get the polarity right (that is, stripe to the left – see pic).

These 1N4733A diodes are NOT an exact match to the original, and do not have a very high current capacity so I was kind of expecting the replacement to blow right away after we plugged it back in. It held just fine. We kept the brake pressed for five minutes straight and saw there were no problems. The diode was running hot, but not alarmingly so. We then pumped the brakes 10 times in succession to see if it would hold up under that kind of stress. Again, no problem.

The immediate problem of the upcoming state inspection appears to be solved. Of course, the real test will be how it handles real-world conditions: driving all day, sitting in the sun for long periods, and whatnot. I figure if it survives the week, it might survive a year or longer.

Just in case, I will go through my stock of electronics parts and see if I can't find a better match if it decides to die sooner than later.  And who knows... maybe I can take advantage of that parts and labor warranty after all.