[urq] High beam indicator stuck on, high beam stalk has no effect- what did I break?

[Scott Justusson]

Dave, I double checked, then grabbed a few relays... and I really think you have this backwards....   Bosch and Hella relays with an internal diode, pin 85 is the ground feed = always.  This is also specified by Bosch (now Tyco) and Hella schematics.  To avoid making the basic mistake of blowing diode protection, I consider all Bosch/Hella relays (outside of the oem harness applications) to be 86 'Hot" and 85 "Ground".  A couple years ago, Bosch (tyco) started to supply all aftermarket relays with the diode to reduce the chance of installed EMF problems in newer cars.

The easy way to check a diode protected relay, is to check the schematic on the relay...   the tip of the "arrow" points toward the "cathode" (12v + voltage side).  I have never seen a Bosch (Tyco) or Hella Relay with cathode to Pin 85.  The good news is, you blow a diode by hooking the relay up wrong, it still works as an 'unprotected" relay.

The better news is that Audi (Bosch/Hella) and Volvo (Siemens) regularly use resistored 85>86 pin relays in the stock panels, which are better and longer lasting interrupts for controlling coil generated spikes.

Back to the switch, a properly operating switch could have the feedback problem.  Here it's more basic, the switch doesn't detent, which means it can't find low beam no matter how many diodes are in the relays.

Cheers and HTH

Scott J




-----Original Message-----
From: djdawson2 <djdawson2 at aol.com>
To: qshipq <qshipq at aol.com>; spotatashleys <spotatashleys at hotmail.com>; s.b.mills <s.b.mills at gmail.com>; urq <urq at audifans.com>
Sent: Tue, Jun 26, 2012 12:15 am
Subject: Re: [urq] High beam indicator stuck on, high beam stalk has no effect- what did I break?


Not saying the stalk isn't the issue, but I've seen this happen where it is, in fact, NOT the issue.  Remember, wen you've relayed your lights, your stalk is subjected to minimal duress, and rarely would fail after you install relays.

Most recently, I installed and relayed euro "dual" H1's on my 930.  Due to ease of installation issues, I elected to go with 2 relays per headlight (1 high/1 low).  I run 100 watt bulbs on the lows, and 130 watt on the highs.

Needless to say, the 930 is a car I use only in the summer.  After sitting through a winter, when I first use it after sitting for months, it behaves almost exactly as you've described.  I flip the high beams on, and then they will not go off... the indicator in the dash stays on as well.  If I cycle them multiple times, the high beams will begin to shut off after a few seconds, then quicker, and finally it reacts as soon as I trigger the stalk.

Why, I wondered.  I did measure some small residual voltage (2 volts) between the 85 and 86 pins on the relay.  These 2 pins power the coil that closes the relay.  I wondered if 2 volts was enough to keep the circuit (coil) closed.  I did some reading, and found (as expected) that it is essentially irrelevant which pin (85 or 86) is powered, and which is ground... as the coil doesn't really "care" about polarity.  However, I did read that relays often use a tamping diode between the pins on the relay, 85 and 86 in the case of Bosch.  This is effectively a one way switch, with high resistance in one direction of current, low in the other.  This is where polarity would make a significant difference.

Long story short, your relays will work if you apply signal (hot) to pin 86 and ground to pin 85, or the reverse.  But if there actually is such a tamper diode in place, polarity will matter, in which case you should insure that pin 86 is your ground, and pin 85 is your hot "signal" power that activates the relay.

If polarity is reversed (pin 86 hot signal, 85 to ground), the tendency for the relay to remain closed does exist.  I would make sure that you have 86 as your ground, and 85 as your "signal" hot.

Dave