I had another thread on troubleshooting the taillights on my 89...this is a bit more focused on the rear lamp relay module...hopefully someone might be able to assist..


Originally my 89 had a flaky right rear taillight. I opened the rear lamp relay module up and found the following inside (see scorched areas in photo 1).


I picked up a used relay unit on ebay...opened it up to take a look and it looked nice (see photo #2). I then ran it for a few days and started to get the fast turn signal and bulb failure alerts going on again... oddly, sometimes the turn signal would be working in the back and front properly, even though the dash was doing a fast turn signal speed. You could let it go and it would stop working in the back....tapping on the unit would trigger it to work again.


So I pulled the case out, expecting to probably have some cold solder joints... instead I found picture #3...what used to be a nice daughterboard was now a scorched mess in the resister R9, zener diode ZD2, and capacitor C4. Is there anything out there that illustrates the schematics for these units? I'm not real confident that replacing this unit or fixing these components will render a stable solution at this point...


Before this unit was swapped, i put in all new bulbs, just to make sure...and went through the front cluster and reflowed the solder to make sure that wasn't somehow involved...
Sort of at a loss of what to do now... all I want is a working relay unit and brake light, I don't really care about the bulb out notification thing..


Pete

 

Pete,

You sparked my curiosity and I examined a spare non-working module I have and low and behold R9 and ZD2 are crispy, never looked at them before. I then examined another spare, but those components were okay, but it's still a non-working module, I replaced it very recently from an ebay purchase. I haven't had time to take out the magnifying glass and examine it closer.

My first thought to your situation is a short hidden in the harness feed side to the module. I also recall some people discovering the fuse block for the applicable side have poor/cold solder joints.

I have a set of the JDHT CD's, but the schematics don't drill far enough into detail to determine the specifics of what is flowing through R9 and ZD2. I believe the daughter board is the Turn Signal Fail Logic component, which makes sense since we both have/had problems with the turn signals operating properly.

I wonder if replacing those components (resistor/diode) with newer components will get the module working properly? When I have time I'm going to open the harness going to the lamp assembly to see if there is damage/corrosion in that harness. I won't get to it until this weekend at the soonest.

 

Thanks Rob, let me know what you find! I'm going to take a closer look at the wiring to see what's in the loop as well. I have a feeling that, if I replace those components, things will work better...not exactly a revelation, though... What's odd is that my taillights actually work at the moment...sporatically. I know if I remove the board, the turn signals will not work, so beyond that..it's sort of a fog on what's happening.






Pete

 

Just out of curiosity... anyone know the original turn signal bulb types on the XJ40? Not the type that Sylvania has in their manual now...but what was originally in published Jag documentation at the time of production? Just curious if there was a substitution at some point...which perhaps works and is close, but perhaps not factoring in this 'sensitive' current detecting relay module?

 

By the way, if you do have your modules open, I'm curious if you can see what the zener diode part # is on that daughterboard I believe it starts BZT03C.. and ends in ..5, but not real clear if it's possibly a:




BZT03C7V5
BZT03C15
BZT03C75


Pete

 

Hi Pete,

I assume our '93 uses the same turn signal bulbs as your '89.

Our owner's manual doesn't list "Turn Signal" or "Direction Indicator" bulbs... As far as I can tell, it calls the front turn signal the "Front parking (side) and flasher lamp," and specifies a "Bayonet double filament 380 long life" bulb.

For the "Rear flasher lamp/stop lamp," a "Bayonet 382 long life" bulb is specified.

For the "Tail lamp," a "Bayonet 207 long life" bulb is specified.

I can't recall the last time I had to replace a front turn signal lamp, but I've replaced rear tail and brake lamp bulbs several times. For as long as I can recall, I've been using 1157 bulbs in the double-filament applications such as the rear brake lamp/turn signals, and I've been using 1156 bulbs in all the single-filament applications, such as the tail lamps. It may be that the later BFMs are more robust, but I've never had any problems with ours, not even after adapting our headlamps from the rectangular Euro style to the older quad-lamp setup. Come to think of it, I never had trouble with the BFMs on our '88 either... Something I'll try to remember to be thankful for!

Cheers,

Don

 

Thanks - Seems in line thus far (right bulbs that I have in there. I pulled the CPU and didn't see anything looking too odd...although there was some strange residue on all the solder points that were connected to the harness. May have been a protective film or something left over from the original solder job, but I'm going to reflow everything, just to be sure...


I looked at my daughterboard on the relay module and just don't have anything left to figure out that BZT03 zener diode (ZD2 on the board). From my original photos, I can make out BZT03C...5, but just not sure what's between the C and the 5. I looked at ZD1, but it's a different diode (BZT03C18)...


Thus far it looks like it cooks...
D4 - 1N4004 diode
R9 - 22 ohm 1/2w (?) resistor
ZD2 - BZT03...5
C4- 47uf 16V Capacitor


Pete

 

Also, I'm matching it up with what Sylvania Osram site gave me - 5007LL bulbs for the taillight, 7506LL for the turn signal...


Pete

 

Quick update on this project - I picked up a later rear module (the plastic black box style that has the clips for the cover... and inside there's only one board, no daughterboard. So far it's been a few days and no bulb alerts, no burned out components and everything's working fine. Crossing my fingers it stays this way for a while..


Pete

 

Pete,

What was the part number of the latest module you installed?

 

It was DBC5249 ... seemed like the last one that the parts book sources crossed referenced over to.


Pete

 

I will wager a Guiness that this problem started as a shorted C4 capacitor and took out R9 the resistor. Bet is that the zener is ok. Replace R9 then C4 with something other than a tantalum. Tantalums are notorious for going short