BauerR

I didn't want to butcher up my factory taillight harness so I bought a brand new Euro harness. It changes the light pattern just slightly. Most notably, the brake lamps aren't dual filament anymore. Because of this, I'm getting the taillight failure message.
my question is, is there a way to track the system into thinking it has the appropriate lighting installed?

Ducman82

never heard of different bulbs being used. got a pic of this difference? the check unit looks for the correct resistance. could just be off brand or different bulbs

BauerR

The problem isn't the bulbs but rather the lack of "low wattages" bulb. The stock car harness is looking for it but the new harness isn't wired for it. So the system thinks the low wattages bulb has failed

davek9

Is this for an S4?
The S3 and earlier only use single filament bulbs in all locations, IIRC S4 uses 1157 for running and stop lamps.

So you have the wrong MY harness, the Lamp Controller can be by-passed at its connector, same as when using LED's.

Ducman82

How Would one use a late harness in an early or vice versa? Now that would be work. lol

dr bob

S4 Euro harness supports adding the rear foglight function. IIRC that uses a 1157 dual-filament bulb same as brake light. So you have low-wattage running light filament to satisfy the bulb-check unit. Memory is that the bulb check unit does not check the rear foglight filaments.

Alan

The bulb check only checks 2 things: rear & side markers (combined by side) and rear brakes. It doesn't care if you have dual filament or single filament brake lights - it only cares about the current draw. The circuits for brake lights and markers are completely independent. Your problem is most likely that you don't have the same number of filaments active as you should have for the markers (or some filaments are not of the correct wattage). You now have two less filaments per marker light circuit - and this makes the bulb check unhappy - because it is exactly as if filaments are burned out (e.g. its doing its job perfectly)

Why buy a euro harness? (unless you specifically intended to make a change). Fix for it? Buy a euro bulb check unit for the correct year as well and adapt the harness.

Alan

BauerR

The Euro harness doesn't have a bucket that will fit a dual element bulb.

It sounds like we are saying the same thing. The factory harness is looking for a low watt signal, which is not being satisfied. Question is, how to we fool it to think it's there or just eliminate the low watt circuit from the board itself.

I changed over to euro spec because is was the only harness available new. My factory harness was rusted and rotten. Wasn't interested in hacking it up. Figured the car deserved better

Ducman82

have you tried bulbs of all the same make/wattage?

jpitman2

Interesting. My 83 Euro (UK spec, C16, RHD) has rear lights that go, from the outside- blinker, reflector, stop/tail, reverse. This means that the stop/tail has a dual filament (typically 21/5 w). Sadly the Tech specs and owners books are almost all US oriented, except for mentioning H4 headlights. How did US cars implement tail and stop lights with single filament bulbs ? Different rear light assemblies?
jp 83 Euro S AT 57k

davek9

They have four segments (outer to inner) Turn, Running, Stop, Backup,
When not in use the segment is dark, Running position uses a lower wattage bulb then the Turn and Stop and Back up.

Alan

This is presumably for the '88 or '89 the OP has - so S4+ lights.

USA: 3 segments of markers in the cluster + rear/side marker per side
ROW: 2 segments of markers in the cluster (no rear/side marker) per side (brake segment is dark except for brakes)

Again - You can buy a Euro bulb check unit to fix this (swap out) OR disable the Bulb Check altogether

Alan

dr bob

Turns out that there are some pretty significant differences between the US and ROW tail lights and the supporting harness connections. The differences are enough for me to say that you can't substitute the ROW harness into a US car with US tail lights. The ROW harness might be a handy source of factory sockets, but if you are splicing stuff in you might as well just splice in the Mazda/Mercury Mariner, Aerostar sockets for a lot less money.

From the workshop manual electrical diagrams for the 1989 cars, I've "cleaned up" the tail light sections so they can be compared:




*** Diagram is corrected to show the ROW Stop and Backup bulb names previously swapped.

BauerR

I still prefer using the Euro harness to hacking up a stock one. Just need to get past this and I'll be perfect

dr bob

the option is to "hack up" the Euro harness to make it like the US harness. Else you won't "get past this". Look at the two diagrams to see what will need to be changed.