LED Bulb Conversions

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
Hi,

Has anyone installed LED bulbs in their tail light sockets? I've found that the extra brightness and instant-on of the LEDs helps modernize the car and provides a factor of safety.

You can go straight to 5x red W5W LEDs in the high mount light with no impact to normal operation, but the 1157 Tail/brake lamps need resistors added to run properly.

I am trying to figure out a way to get my 1157 LED brake bulbs to work. I used a similar approach on my mk4 where you can use the 31 (ground) and 58 (tail light positive) open pins on the bulb holder to easily "splice" in a set of resistors without cutting into the factory harness. I thought I could connect two load resistors in series to just the driver side rear bulb holder, effectively putting them on the common ground for both the tail and brake lights. This appeared to work when the car was OFF, but when the car is running (engine on), the center mount brake light runs at all times at about half power (without brake pedal depressed), so I've since removed the LEDs and gone back to the incandescent bulbs.

Without the resistors attached, the center mount light is on at full brightness at all times. This happens because there isn't enough resistance in the circuit to prevent the high mount brake light from lighting (my guess is the current jumps the switch or backfeeds from somwhere.) I'm not surprised since this also happens on the Mk4 cars.

I haven't tried it yet, but I'm thinking I should just add another resistor and try again?

The Mk3s seem to work differently since they appear to be wired a little differently – both tail lights share a common ground wire and the passenger side has a different plug going to it. But perhaps I have the resistors attached to the wrong point (they are effectively wired in parallel with the circuit and not in series.) My feeling is that I'll have to splice the resistors into the harness on the passenger side.

Perhaps I should just abandon this project given that the resistors will be pulling current at all times and could overheat or melt something in the trunk.
 
Last edited:

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
Ok, looks like I just had it hooked up wrong. I’ll post a DIY one of these days but the pins should be 31 and 54 on the backside of the driver side bulb holder, hooked up to two load resistors in series. Everything works as advertised now.
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
Fwiw, I’ve never needed to add resistors to the circuits. Both of my B4s have LEDs for tails and markers. The most I’ve done is add a LED flasher relay.

-Todd
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
Fwiw, I’ve never needed to add resistors to the circuits. Both of my B4s have LEDs for tails and markers. The most I’ve done is add a LED flasher relay.

-Todd
That’s interesting. It didnt work for me that way, but I’m not in a B4.

In terms of the flasher relay, I bought an “adjustable” LED relay for the turns but it flashes too slowly even at max speed. Which one did you use?
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
I can’t imagine the circuits being that different between models.

The flasher relay wasn’t anything special. I bought it from eBay or Amazon and I doubt I paid more than $5, for it.

-Todd
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
Both cars (B4 / Mk3) use CE2 electrics so other than the length of the wires there's virtually nothing different about the lighting systems or the majority of the electrical systems.

They use the same fuse / relay panel, same column switches, ignition switch, headlight switch etc.

Steve
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
The wire colors for the lighting circuits on my 81 Rabbit project car, matched those from the 97 B4 donor.

I thought load resistors were a fix for newer can-bus cars.

-Todd
 
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