Can't get rear fog light to work (relay wiring) HELP!!!!!

[longtallsally]

OK, this is just plain killing me.  I have absolutely NO clue what I've done wrong.

I have been trying for the past 5 days to get this to work and I can't get it to work.

So this is following the instructions from John via:  http://www.m42club.com/forums/showthread.php?t=37

Here is in a nutshell what I have wired:

- 1 wire to the switch (goes to terminal 85 on the relay)
- 1 wire from the fog light to the relay (terminal 87 on the relay)
- 1 wire from ground to the relay (terminal 86)
- 1 wire from constant hot (directly from the battery) to the relay (terminal 30)

- I have one more wire running off terminal 87 that is wired in conjunction to the rear fog that will illuminate the light in the cluster, but I've not even gotten to the point of putting the cluster back in.

So here is the deal.  I changed his process only very slightly to what John did in that as opposed to giving the switch power from a separate circuit that is ignition hot, I am using the power for the OEM front fogs to send juice to the switch.

For the LIFE of me, I cannot figure out what I have done wrong and have tested every darn thing I can imagine and quintuple checked how I should have the relay wired, yet nothing.

Here are the tests I've performed:
- did a redneck test and simply took the fog light lead and put it to battery power and the light came on.  Check, it's good.

- did a continuity test on the switch to make sure it will complete a circuit.  Check, it's good.

- Verified I have a good ground for the relay.  Check, it's good (I ended up running it directly to the battery neg terminal).
 
- verified that the hot lead to the switch is in fact hot.  Check, it's got juice.

- totally eliminated the switch all together, and ran a jumper directly from the battery to terminal terminal 85 on the relay (basically substituting the switch for the jumper) and the relay activates and the light comes on.

- ran a continuity test for the wire from the relay to the switch by putting the wire to ground in the trunk, and then testing for continuity by using the meter by the switch wire to see if I get tone (this basically tests if I have a short in the wire, and/or a break somewhere).  Check, it's good.

- verified the front fogs still work.

- tried to have the front fogs on at the same time and independent.

- found another ignition hot source of power (not involving the headlight switch at all) to see if that is it, and nothing.  FAIL on this test.

- tested that I had the correct "hot" lead for the rear fog light side of the switch by testing which one has juice for the front fogs.  Check, it's got juice.

- verified that the other terminal goes to ground for the front switch.  Check, it's got continuity.

- tried to verify the same thing on the rear fog light side of the switch.  FAIL, there is no continuity.

So in other words, my circuit is not completing from the switch somehow- the wire from the relay to the switch is not going to ground to complete the circuit.  But I must have the relay wired correct and it is good b/c I can get it to activate with the jumper wire.

I have wired countless lights before and am obviously missing something simple, but I simply cannot put the pieces together.  AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[longtallsally]

I just did another test.  I took the switch and put it in the trunk and ran a wire from the switch to terminal 85 and then a wire from the battery to the other terminal on the switch.  Turn the switch on and it works.

So again, I know I have the relay wired correctly and confirmed this.

I also tried again to take the switch to the cab and try to use another source of ignition power.  Nothing.

This is literally driving me insane.  Every project on THIS particular car is a horrific exercise in frustration.  Simple updgrades and repairs that should only take a couple hours end up taking days, weeks, or months, literally.  I've never had this many problems with any of my other E30s or cars for that matter.  I think I have a possessed car...

[DesktopDave]

It's a normal relay, right?  Not one of the diode jobbies?  Switch 85 & 86 to test.  Might be too much resistance in the wire as well.  Seems like you've totally exhausted any possibilities, I can't find any flaws in your troubleshooting.

I feel your frustration.  Some days it works, some days it doesn't.

[longtallsally]

Thanks, Dave.  I think the only other one who would set me straight would be bmwman91 that I can think of.  

In terms of resistance, not really possible as I used all brand new wiring...

Anyway, I'm going to try one last thing today; I'm going to completely eliminate the headlight switch from the operation and try it just to a different ignition hot source.  The only thing I can come up with is that I'm canceling out something and the work I've done with the relays to get the high and low beams as well as fog lights on is causing some electrical "confusion" in the system thus not allowing the circuit to be completed.

So, I'll set this up and report back.  This car is truly exasperating at times...

[longtallsally]

Figured it out.  Sheesh, that was an exercise in frustration.  Probably close to 20 hours to get 1 flippin' bulb to work.

So the problem turned out to be 2 fold.  My wire that I thought I did a positive continuity test running from the switch to the trunk in fact did have a break in it.  Second was that you canNOT use the headlight switch power going to the front fog light to get it to work.  I cannot give a specific reason as to why, but I suspect it is just as I said before that it has to do with the other light relays and all that nonsense.  Oh well, now I can move on to other frustrations, like the water leak I have somewhere, and a new oil or power steering leak.

Sometimes I think I should have been more patient and waited for a better example...

[YetiX]

Figured it out.  Sheesh, that was an exercise in frustration.  Probably close to 20 hours to get 1 flippin' bulb to work.

So the problem turned out to be 2 fold.  My wire that I thought I did a positive continuity test running from the switch to the trunk in fact did have a break in it.  Second was that you canNOT use the headlight switch power going to the front fog light to get it to work.  I cannot give a specific reason as to why, but I suspect it is just as I said before that it has to do with the other light relays and all that nonsense.  Oh well, now I can move on to other frustrations, like the water leak I have somewhere, and a new oil or power steering leak.

Sometimes I think I should have been more patient and waited for a better example...

That's crazy talk SFS.  You got that one because it needed the love! :p

Glad you finally got the fog to work, but your explanation makes it sound like our cars have CANBUS or something.  When you get back here you can help me hook up a rear fog on my car.

[longtallsally]

I learned to use a meter and cut my teeth on 80s vintage VWs.  It is pretty common knowledge that VWs are pathetic when it comes to electrics, so I got a lot of practice.

That said, I have found 3 primary uses for a meter:
1) Continuity test
2) Voltage test
3) resistance test

I've done some uses otherwise in other projects around the house and such involving diodes and the like, but the above are the primary ones anyone uses and they are really quite simple.  I'll describe how I use each one, but I am NOT a EE or an electrician, so this is more from my personal use knowledge and thus should be taken with a grain of salt and not gospel.

Continuity test- you find the correct symbol on the dial and if you have a cool meter, you will get a tone when the 2 probes are touched.
- uses:  To test for ground, short, or if a circuit/wire is complete/connected

- ground procedure:  touch one end of a probe to the end of a wire that should be a ground wire, then another to a place on the chassis where ground should exist (grounding post, bare metal, etc.).  If you get a tone, it's a wire that has been grounded well.

- short procedure:  You keep blowing fuses but have no clue why.  Touch one end of the probe to the HOT wire and the other to chassis ground.  If you get a tone, you have a short in your hot wire.  (these suck, b/c it's a wild goose chase to find the place where the wire is chaffed)

- circuit/wire procedure:  (As I ran into) You are not getting juice to something you should, or you don't know if 2 components or systems are connected in one way or another.  Simply touch the probes on each end of the wire or circuit and you can see if you have "continuity".  For example, I want to find out if 2 systems have the same source of power, I can test with this.  Or if I want to test if a wire that I've run and put in a couple couplers made it through.  No tone, you have your answer.

Voltage Test- Pretty straight forward here.
- uses: test for how many volts you have, or if a circuit is ignition hot or not.  
- procedure: Red probe (on most meters) to hot wire, and black probe to ground.  Measure the voltage.  This can test if you have a drain on a system with the car off, or how much juice a component is sucking down, or even the health of your alternator.  Obviously, you test for ignition hot with the key on and off.

Resistance test- determines how much loss from bad wires (black wire disease or the like) or possibly if a circuit is arcing.  
- uses:  The most common one I've had to use this for is testing spark plug wires.
- procedure:  touch the probes to each end of a wire and take a reading.  In spec, good.  Out of spec, wire is wasted.

This is stupid rudimentary, but thought it might give you a little insight and will probably cover 99% of the tests you would do on your car to check functionality or the like.

[DesktopDave]

Good to get that all posted.  I'm curious about the light switch too.  I've seen them do all sorts of funky things.  With my Delphin 325e you can turn off all the interior lights, just turn the headlight knob past max brightness.  I should have posted about that.

[longtallsally]

Good to get that all posted.  I'm curious about the light switch too.  I've seen them do all sorts of funky things.  With my Delphin 325e you can turn off all the interior lights, just turn the headlight knob past max brightness.  I should have posted about that.

The light switch is REALLY simple, yet quite effective.  It looks like a window switch and has 4 posts on the back; 2 for the front light and 2 for the rear (just like I posted on John's thread).

There is no common ground, relay, electromagnetic this or that, anything like that.  It is merely a toggle switch to complete a circuit.  If you took one apart, you'd see just how very simple, yet elegant it is.  The best part is that they are completely rebuildable.

I re-read what I wrote and I probably should put in more detail, but it's enough to get someone googling to find out how to do something.