Schocki

The mentioned part is listed as a resistor in PET, but I can't find it in any wiring diagram. It is responsible for the excitation current to the alternator (I think), where is it mounted? It is part number 16...

Mrmerlin

from the picture it appears to go into the back of the instrument cluster

Rob Edwards

Greg had a car (want to say an '89GT) that had a a problem with that resistor. Can't remember what the symptoms were. I think that's about when he grew the beard, 'cause he'd pulled out all his hair on that one. IIRC it's mounted somewhere up behind the dash, between the pedals (?)

Schocki

Thank you guys, I will forward the info to the forum in Germany.

ROG100

I just had a customer order one of these - first time ever. For some strange reason I had 4 in stock.
Looks like they are only used in conjunction with the digital dashes.
Anyone know what they do?????
I hope it is not important because they are NLA from Porsche.

karl ruiter

If its what I think, it provides a trickle of current to the alternator so it will charge. Should not be hard to fix or find an alternate.

Wisconsin Joe

Why am I not terribly surprised you have a part in stock that:

1 - Nobody else has.
2 - Nobody ever ordered
3 - Nobody knows what it does.
4 - Is NLA from Porsche.

Schocki

Hola mi amigo,

1. They don't fail very often and the resistor is in general very robust.
2. Yes, they are used in the digi dashes only. The foil dashes have a different resistor.
3. Fact: to produce power you need a stator and a rotating magnetic field.
What this part does? Easy .It provides the exciter voltage to power the rotor in your alternator before you start the engine and the regulator kicks in. The main difference between an alternator in dynamo is the rotor. The dynamo uses a rotor with solid magnets and therefore a fixed magnetic field. Here, power output varies with RPM. Simple as that.
Alternators are different: their rotors use coils to generate a magnetic field. When you turn your ignition on, the battery light tells you that there is current flowing from the battery through the exciter resistor via the battery light to the regulator. The rotor is powered, provides a magnetic field and you're good to go. As soon as the motor runs, the light will be off. This indicates that the regulator in the alternator took over and is charging the battery. The regulator varies the amount of current to the rotor as needed to keep the battery charged and all connected components going. This way constant voltage is supplied.
4. In theory this resistor can be fixed if you know the resistance and the wattage. But it's good that you have some in stock.

Info: This is also the reason why a car with a stick shift and a completely flat battery will not start if towed or pushed. No current in the rotor, no power provided even if the car is towed to a descent speed. BUT there is another good reason why this should not be attempted: if the car starts and the battery has close to no voltage left, there is a good chance that the alternator will be destroyed if the engine fires up. This has the same effect as if you disconnect the battery while the engine is running, immediate destruction of the alternator

Below a picture of the location of this part. Left of the accelerator mounted on the brake pedal bracket.

Ed Scherer

That sure looks like the resistor that's in series with the '89 and later instrument cluster backlights; I believe it's to reduce current to those four backlight bulbs, which have a tendency to melt the surrounding plastic. Definitely is, if it's got BK/BL wires connected to it.

See the threads 89GT Pod Lights Out - Center Console On and Digi dash light issue.