brake warning light module in relation to glow plug relay

[92EcoDiesel Jetta]

after replacing a burned out bulb in the brake warning module, the brake warning light is now always on, even with hand brake switch and brake reservoir level sensor wires disconnected. Looking at the wiring diagrams, there is a connection from the brake warning moduke to the glow plug relay. What is the purpose of that? I am wondering if there is a problem in the module, which also is a seat belt warning and has a transistor, 2 resistors and a diode. I have not tried to trace out the circuitry yet.

Here's the diagram for the brake warning module. If you follow the rectangle 17, it goes to the glow plug relay. In the next diagram.

[TylerDurden]

I haven't sussed it totally, but I rekon the passive interlock versions kept the GP relay from getting triggered and timing out the relay (until the belts are fastened).

[92EcoDiesel Jetta]

I haven't sussed it totally, but I rekon the passive interlock versions kept the GP relay from getting triggered and timing out the relay (until the belts are fastened).

You mean if the seat belt is not engaged, it would lock out the glow plugs? That's quite drastic.

[TylerDurden]

Yeah. I haven't tried it on my eco, but if the interlock defeats starting, it would make sense to defeat the GP relay too. Otherwise, the driver could leave the key on while fastening the belt and the GP relay could time-out.

[92EcoDiesel Jetta]

Does your Eco require the seat belt to be engaged before allowing engine start? Mine does not and I assume it was defeated.

[TylerDurden]

Yep. I started it a couple times (seatbelt fastened) and shortly thereafter removed the engine, so testing now could be complicated.

[bajacalal]

I believe the seat belt-start interlock is a 1992 only feature of the mk2. I don't remember if the Bentley accurately mentions this wiring revision. I think it is commonly defeated by jumping the start wires going to/from the interlock relay.

[92EcoDiesel Jetta]

I believe the seat belt-start interlock is a 1992 only feature of the mk2. I don't remember if the Bentley accurately mentions this wiring revision. I think it is commonly defeated by jumping the start wires going to/from the interlock relay.

91 and 92 Ecodisels are the only odd balls with this crazy interlock scheme? I looked further at the elec system diagrams. In addition to the seat belt starting  interlock relay which control the glow plug relay, there's also a starter interlock relay to cut out the starter. I have not looked to see if these relays are present or not or how they were bypassed. Will do so when it stops raining.

Good news is the brake warning is working now. When I replaced the bulb, I failed to notice a burned trace in the module.

[Jaceb-GLI]

No. All VWs with passive restraints have to have the belt buckled.
my ECO has always started without the belt plugged in, now I have a complete 3pt belt swap and I didnt even have to tie the wires together.

[TylerDurden]

OK, I took a better look at the Bentley... the "seat belt warning control unit" controls the "starting interlock relay" which feeds buss 50 (starter & GP relay). I assume the connection to the brake-light is just supposed to extinguish the light when cranking.


(Edit for nomenclature)

[92EcoDiesel Jetta]

Looks like all my relays are in the right places per the Bentley.
I am not going to rip it apart just to find out how the seat belt interlock is bypassed. It is working fine the way it is. Broke a spade on the parking brake switch trying to put the connectors back on. I am not replacing it and will do w/o it. The brake fluid level warning is working now, that's all I care about. My master cyl has a slow leak. I'll try pin pointing the exact leak spot and see if it can be stopped w/o replacement.

[TylerDurden]

Looks like all my relays are in the right places per the Bentley.

Except relay #9 appears to be missing in the pix.

[92EcoDiesel Jetta]

Looks like all my relays are in the right places per the Bentley.

Except relay #9 appears to be missing in the pix.

You're right. That's probably how the interlock is defeated.

[fatmobile]

 The 2 are somewhat connected but it's more like they are both connected to the 50 starter wire.