Headlight Problems

[Fierofool]

I've been helping Richard with some problems on his 86GT.  It was throwing an EGR, a TPS, and a MAP code, as well as the speedometer was fluctuating wildly.  The voltmeter was nearly pegged out. 

I checked charging voltage and it was putting out just over 19 volts.  He had previously replaced his alternator twice.  Today his service shop said that it had the wrong pulley on it and changed out the pulley.  Richard says it seems to have solved all the problems but the EGR.  I had identified his EGR valve as having a bad diaphragm and sold him another valve.  It will be installed tomorrow.

Oddly, the SES light  came on only briefly on his drive home after having the alternator pulley replaced.  But there is another problem I think is associated with the high voltage.  His headlights don't illuminate any more.  Neither high nor low beam.  All other exterior and interior lights work. 

I can find no listing in the circuit breaker panel for headlights.  Is there something elsewhere that could burn out?  Fusible link?  I'm actually thinking it may have burned out the light switch.  Any ideas, anyone? 

[TopNotch]

There's a way to try another headlight without changing the headlight. Go to the parts store and get the cheapest H4 type headlight bulb you can find. It has the same kind of connector as the sealed beam bulbs in a stock Fiero. Pull the connector off the back of one headlight, plug in the H4 bulb, and turn the headlights on. If the H4 lights, the headlight is burned out.
It's best to do this with the lights up and the motor disconnected (no surprise movements).
ps. And the pulley size doesn't really make any sense. The alternator is supposed to be regulated to put out the same voltage regardless of speed (unless idle is too slow). Sounds like either a bad alternator, or a bad connection to it.

[GTRS Fiero]

Do his headlights open and close?  Do the relays click?

A DVM is your friend.

My EGR did the same thing.  Put the old valve back in, problem gone.

I'm thinking about that pulley.  If the pulley was too big, the alternator would spin more slowly, like the engine was running more slowly; if the pulley was too small, the alternator would turn more quickly, as if the engine was revved up.  Since the alternator has no idea what the engine RPM is, this doesn't make sense.  The alternator should come with a pulley matched to its voltage regulator.  Possibly it was a high output alternator, but that is high current.

As we all know, V=IR.  If V=19, obviously we need to look for high IR.  A poor ground could cause high resistance.  With the new pulley (probably larger), the current probably dropped, and isn't making a good enough connection.  The resistance would go to infinity, the current to zero, and the voltage to zero.

I suspect bad grounds.  I'm not sure how that high voltage may have affected the ECU, but certainly it wouldn't affect the headlights at 19V.

Since everything else works, the circyuit may have been backfeeding.  No, I don't know which circuit.

Of course, this post is probably worth less than you paid for it.

[f85gtron]

As we all know, V=IR. 

Huh? Wutt? Careful with your assumptions! All I know is wires should throw sparks (from magic voodoo) when they touch. Logic then tells us that no sparks=no magic (or voodoo). I have no i.d. what that other stuff is you're talking about.

[GTRS Fiero]

Sparks in old plastic car=fire!

Voltage = current * resistance.  You have to get the units right, though.

[TopNotch]

As I said before, the alternator regulates it's output. It does this by measuring the voltage. The line it measures goes though the alternator light on the dash (which is why it doesn't work if the light burns out). There could be a bad or dirty connection somewhere causing it to read back only 13 volts when it puts out 19 volts. It could be anywhere. All connections should be checked with an ohm meter.

[GTRS Fiero]

You have to wonder if, once the problem is corrected, the battery will slowly drain.

A bad or dirty connection would increase resistance.

Logically, by looking at a wiring schematic, someone who knows how to read a schematic and has done a wiring harness could isolate the most likely places to check for issues.  I mean, the car starts, so not that circuit.  The voltage is off, so that circuit.  The headlights don't work, so that circuit.  What do those 2 circuits have in common?

I usually start with continuity checks.  Bad grounds seem to plague the Fiero.

[Fierofool]

I knew that the pulley diameter didn't make a difference, but he said the problem seemed to go away.  It's common to get a pulley that's too narrow, but that just shreds belts.

I told Richard to have the Advance store he works at to unplug and put a multimeter on the headlight harness to check for voltage.  He said his store doesn't do all the free stuff like other Advance stores, so tomorrow he's going to plug in a spare bulb as a test.  I didn't know he had spare bulbs.

Headlights system works normally, other than they don't illuminate.  That's the only problem at the present time.  Other than at some point when the other alternators were replaced, they discarded the shield that mounts on the alternator to direct the air from the cooling tube. 

[GTRS Fiero]

It's more likely that they bumped whatever wiring is causing problems.

Out of curiosity, did the headlights illuminate before the pulley swap?

[Fierofool]

No, they didn't.  He recently had the current alternator installed.  As he was driving to work, I would estimate a distance of 20-25 miles, he said that in retrospect he didn't think the lights were working.  He also noticed the erratic speedometer and high voltage on the voltmeter and the SES light was coming on, or was staying on. 

He's going to do the spare bulb test today and let me know what happens.  Because he drives in rush hour interstate traffic on his way to work, he probably would have only used low beam.  The absence of a high beam makes me think it isn't the bulb.  I found a circuit breaker in the headlight switch schematic that could possibly be the culprit.  When I hear from him today regarding the bulb test, we'll go from there and swap out the switch with one that I have. 

[Slyp]

 Sounds like an interesting problem. Having read the last entry it sounds like the low beams work but the high beams dont work?  The print I'm looking at sort of makes me want to look at the head light dimmer switch which is on the turn signal lever.  Click on click off. If the low beams dont work then I would look further back which looks like the head light switch.

[GTRS Fiero]

Dimmer, huh?  I thought of it as the high-beam switch.  My understanding from reading this was that none of the headlight bulbs would illuminate.

[Fierofool]

Michael, you're right.  Neither high nor low beam would illuminate.  He was running Silver Star headlamps.  And I was incorrect about the overcharging problem going away when the pulley was changed.  He actually replaced the alternator and in the process, they saw that the new one had the wrong pulley, so they swapped out the pulley at the same time.  With the change of alternators, the problem went away.  The pulley was incidental to the alternator replacement.  It still doesn't have the shield on it.  Anybody have one? 

Richard had a chance to test out a regular sealed beam this afternoon and found that it illuminated on both high and low beam.  The problem was that the Silver Stars had burned out.  Likely due to the 19+ volts being pumped into them. 

So, the problem has been solved and all is well, now.  Thanks, everyone. 

[GTRS Fiero]

I was wrong, too, about the headlights not taking 19V.

I'm glad to read that the problem has been solved.  I'm a bit confused on why the previous alternators didn't solve the problem, though.

[Slyp]

Sounds like one of the problems was the output of the alternator.  I seem to remember that if the output of the alternator is say 12 volts you are really reading the battery and not the alternator.  If I remember right the output should be between 14 and 16 volts.  Because you dont need the battery to run the car you just need it to start the car. The alternator will run the car after it is started.