spandak Dork
3/21/23 12:11 p.m.

I have pulley/belt noise coming from the engine on my 986 2.7. This has been going on for a while, but with a twist (for me). It comes and goes. When it's damp out and first start in the morning I'll get a whine just like an idler pulley is going bad. By the end of the drive to work it's gone. I don't notice it on the drive home but it might be there at the beginning. 

I inspected all of the pulleys a few months back and didn't find anything conclusive. The only one that wasn't perfectly smooth and quiet was the AC idler. However, turning the AC on and off has no effect. I think this is weird. Any tips before I throw money at it?


I'm trying to wire some aux lighting on my wife's car. I want the lights to come on with the high beams, ideally with headlights on or off. The car has DRLs (high beams) that are pulse width modulated through the BCM. 

My idea was two relays in tandem, the first comes on with the low beams and the second triggers the light with the high beams but this just leaves the high beam relay buzzing like a bee. Also this would only work for high beams with the headlights already on. I can't tap the high beam fuse because it's powered when the vehicle is on. The BCM does everything. 

The current solution is to tap the fog lights so when those turn off (high beams on) the aux light is triggered. However, this means leaving the fog lights on all the time. Not ideal. 

Is there a voltage sensitive relay maybe? Some other wiring configuration I haven't thought of?

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
3/21/23 9:59 p.m.

Use a DPDT relay on the low beams.  DPDT relays have two contacts; one that is hot with trigger power, and one that is hot without trigger power.

Like a normal relay, but the continuity switches to another terminal instead of just off.

So you could provide power to the hot side of the relay from the light switch and your trigger would be the low beams.  When the low beams go off,  the relay de-energizes, connecting the power from the light switch to the aux lighting.

This is, of course, assuming that the aux lighting fits within the amperage capacity of the light switch and its wiring.  If not, you should have this relay trigger a second relay with adequate amperage capacity for the aux lights.

That is to say... if you're adding a 0.5w LED to make the hood badge glow, no worries.  If you're adding two 55w incandescent fog lights, second relay.

Basicaly, a DPDT relay lets you select the output post that is either hot DURING trigger, or hot when the trigger is not there.  Instead of making a trigger off the high beams, you're making a trigger off the absence of low beams.

spandak Dork
3/22/23 12:16 a.m.

In reply to Curtis73 (Forum Supporter) :

Hmm, couldn't this work with using a regular relay but running power to the 87a pin instead of the 87? I might be misunderstanding. 

Also, low beams stay on with the high beams. Separate bulbs and housings. 
2018 Crosstrek if it's helpful. 

The only positive input I can think of is the high beams (without going straight to the switch before the BCM, not excited for that). For a negative input, so to speak, I could use the fog lights like I mentioned. When those turn off the aux is triggered. But that means anytime the lows are on and the dogs are off it's coming on. I had a switch on the dash so this could work it's just not very elegant. If there is more than one if-then my wife won't be very interested. 

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
3/22/23 10:46 a.m.

If your relay has an 87a, then it's not a normal relay, it's already a DPDT.  Regular relay would have 4 pins, but yours likely has 5, yes?  If so, you already have DPDT.

If there is a PWM wire coming out of the BCM for the highs, there might be a 12v input that is only hot when highs are on?  He says knowing that probably isn't true?  Does the BCM power the highs when they're on (not DRL)? or does it signal some other relay?  If so, you could tap off that relay to get the signal.

I guess I'm saying that there might be a wire that is 12v hot during high beams that isn't hot when it's PWM.  Don't know Suby electronics well enough to advise where it might be.

spandak Dork
3/22/23 9:48 p.m.

In reply to Curtis73 (Forum Supporter) :

Oh! Makes sense

hmm. More research required. I think I have seen a high beam relay in the fuse box. Might be able to tap that upstream. 

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
3/22/23 11:15 p.m.

Something tells me there has to be a 12v signal somewhere that goes to the BCM that tells it when to PWM and when to be on full.  That's likely your huckleberrry.

jfryjfry SuperDork
3/23/23 9:04 a.m.

If you have a bad idler, I'd replace it regardless.  If it seizes - even if it's just the ac -, it could cause the belt to come apart  which could lead to a ride on the back of a hook. 

im not following when you want the aux lights to come on...  with high beams I get but also when the lights aren't on?

spandak Dork
3/23/23 10:41 a.m.

In reply to Curtis73 (Forum Supporter) :

Makes sense. I'll dig around. I don't have a wiring diagram and I'm not sure it's old enough to be out there. Might be able to get one from a mechanic friend. 

jfryjfry: I know you're right but I am avoiding the wallet pain that would come from that replacement. I need to pull things apart again and take a look. It's been a while. 

For the lighting: ideal case is aux lighting is triggered with the high beams in any scenario (flash to pass is what I have in mind). I have a switch on the dash to turn it off completely for day to day driving.

I would settle for aux lighting with the high beams and low beams on. 


If I can find the BCM trigger wire this all becomes trivial. 

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