Strange Electrical Problem

[aormsby]

Ok so I've been fighting some electrical gremlins lately and I think I'm at the point where I need some outside input.

 

Here's the situation:

 

I'm not getting any power to my radio and the HVAC controls have some power but not all. What I mean by that is that it will illuminate and when I turn the fan dial from 0 to 1 I can hear the relay/switch click behind the dash, but the fans won't turn on. The cigarette lighter has power and works fine. I've checked fuses and they are fine. My horn does not have power either. In addition to all of this, none of my brake lights illuminate. I don't know if that is related or not, but it is a problem as well.

 

Any input would be greatly appreciated!

 

Edit: Forgot to mention, the car is a '95 Brighton

[wtdash]

.02: Try swapping relays.

 

Find KNOWN good one, swap w/one that controls something that's not working, etc. (cars should be off between swaps, BTW.)

 

Note: I know 'electricity runs thru wires' but not much else w/wiring (and now we have 'inductive' charging, so I'm really screwed.)

[Setnev]

My HVAC lights and switches intermittently work on my car. I thought swapping the HVAC control system would fix it, but then I figured out there is a problem with the connector. I just hit it when the lights and blend switches malfunction and it comes back on. Now I don't condone smacking your radio or HVAC to see if it works.

 

I did, however, check the FSM and it looks like everything you're explaining is actually run off of multiple fuses, not just one.

 

The HVAC system runs off of fuse 15, 20, & 21. The audio system runs off of fuses 17, 22, & 25.

 

Looking at the power distribution on those circuits, check fuse SBF-3 (45A fuse) under the hood and fuse 18 in the car.

 

There is reference to those, even though they don't specifically state they control those circuits. If a short on a another system went further back to the main harness, it could have blown the main fuses under the hood (SBF's). Ironically, SBF-3 provides power to the in-car fuse box for fuses 6, 12, 19, 20, 21, 22, 23, 24, & 26, which provide power to the horn, HVAC blower motor relay, and radio fuse, just to name a few.

[doublechaz]

Also, there are grounds on either side of the trans hump about even with the center console. They might be coroded from being in the rust belt or from spilled latte.

 

They are a little burried, so you might ohm from points that should be ground at the connector to a known good ground.

[aormsby]

Looking at the power distribution on those circuits, check fuse SBF-3 (45A fuse) under the hood and fuse 18 in the car.

 

 

 

I gave them another look, and none of them are blown. I'm not really sure what to do next. Other than a blown fuse I don't know what would cause no power to be sent to all of these functions.

 

 

 

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[aormsby]

Also, there are grounds on either side of the trans hump about even with the center console. They might be coroded from being in the rust belt or from spilled latte.

 

They are a little burried, so you might ohm from points that should be ground at the connector to a known good ground.

 

 

 

They looked fine, but I cleaned them off anyway. Unfortunately didn't help

 

 

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[aormsby]

Is there any chance this could be related to the ignition? I was having some issues with that a while back, but have since fixed those

 

 

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[Setnev]

Only two things that could cause it if it's not fuse related is a physical break in the main wire from the underhood fuse box or something in the ignition switch not working. A while back, my dad and I had a 96 Intrepid we were fixing to flip and he replaced the ignition switch because we bought it at auction with no key and no battery. When he replaced the ignition lock cylinder, the radio, AC, and gauges stopped working. Fearing the worst, he called me and I looked at it. The plastic box at the end of the lock cylinder came apart ever so slightly and caused the pins to not touch completely. I snapped it back together, problem solved.

[twisty]

fuses can be failed and still pass electricity through them, ive seen it on many different car makes. one recent one was a mid-2000s cadillac that had starting and intermittent electric issues in the cabin, the main fuse tested good with a test light. i finally put a meter on it, showing that it had almost 3 million ohms resistance. traded it out and the car started working again. may not be your issue, but it is in the realm of possibilities

[aormsby]

Only two things that could cause it if it's not fuse related is a physical break in the main wire from the underhood fuse box or something in the ignition switch not working. A while back, my dad and I had a 96 Intrepid we were fixing to flip and he replaced the ignition switch because we bought it at auction with no key and no battery. When he replaced the ignition lock cylinder, the radio, AC, and gauges stopped working. Fearing the worst, he called me and I looked at it. The plastic box at the end of the lock cylinder came apart ever so slightly and caused the pins to not touch completely. I snapped it back together, problem solved.

 

 

 

I'm willing to bet it's something in the lock cylinder then. The problem I had with it about a month ago was that the key physically wouldn't turn at all. I tried messing with it (not forcing anything) daily for about a week and finally it just eventually turned and started right up. Thinking about it now this is probably when the electrical problems started (I can't say for certain though because the car was on jack stands for about 3 weeks after that while I was replacing a blown diff). I have a parts car that I'll take the ignition from and hope that things will be fixed.

 

Thank you for all your help!

 

 

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[aormsby]

fuses can be failed and still pass electricity through them, ive seen it on many different car makes. one recent one was a mid-2000s cadillac that had starting and intermittent electric issues in the cabin, the main fuse tested good with a test light. i finally put a meter on it, showing that it had almost 3 million ohms resistance. traded it out and the car started working again. may not be your issue, but it is in the realm of possibilities

 

 

 

Yeah just to be safe I did put a multimeter to the questionable fuses and found nothing out of the ordinary with them, which was frustrating because if it was just a fuse it would've been much easier.

 

 

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[Setnev]

Before you go ripping apart the column to replace something that may or may not be defective, try some of these steps first.

 

First go under the dash and locate these connectors

http://i.imgur.com/A1R6a3f.jpg

Unplug them and plug them back in. Make sure the connections are tight and clean. Maybe spray some electrical contact cleaner in there for safe measures. Of these 4 connectors, B36 and B37 control power control to the HVAC and Radio and B38 provides ancillary controls to both systems.

 

After that if it is still not working, more in depth troubleshooting is needed. This is going to be a lengthy writeup, but it should help determine where your fault is. Your multimeter should be capable of measuring Ohms resistance and at least 20 volts.

 

Condition: We know that fuse SBF-3 under the hood is good, but no power to various systems (ie. HVAC, radio, or horn).

Testing: Pull SBF-3 and probe the fuse box connector with the negative attached to a body ground. 12+ Volts should be read from SBF-3 with key in On position. Switch your multimeter to measure Ohms resistance, probe the opposite terminal (negative) using the positive lead to the terminal and negative to body ground. You should get a reading. If not, you have a bad ground connection at SBF-3. If both leads check out fine, continue on.

 

I'm going separate by individual system to keep it easy to read.

 

Testing HVAC system:

 

Condition: SBF-3 tests with 12+ volts with key on, ground connection has continuity, 45A fuse is good. No power to HVAC system

 

Testing: Pull fuse 15 in the interior fuse box. Check continuity of fuse and for contact corrosion. If continuity and corrosion check passes, probe the fuse panel contacts for fuse 15. Check for 12+ volts on the positive side with the key on, engine off. If 12+ V are showing, connection between SBF-3 and Fuse 15 is good on the power side. Switch your voltmeter to measure Ohms resistance. Probe the negative side of the fuse with your positive lead in the fuse connector and the negative lead to a clean body ground. If it registers a reading, ground connection is good. Repeat for fuse 20 & 21.

 

Condition: Fuse panel checks out, fuses 15, 20, & 21 have proper voltage and continuity to ground. HVAC still no power with key on.

 

Testing: Locate connector B36 in the driver side kick panel. There is a connected plugged into it. Unplug the connector from B36, that connector will be known as i1.

http://i.imgur.com/njVe2YV.jpg

i1 is the direct connection that controls every HVAC function including all the actuators, blower motor, and relays. Turn your fan switch on high and ground pin 13 (Green/Blue wire) on B36.

http://i.imgur.com/fcQTHpS.jpg

If your blower motor turns on, you may have a short between the i1 connector and your HVAC control panel, continue to next condition. If the blower motor does not turn on, there is an issue with the blower motor relay itself or the harness that supplies it power.

 

Condition: Blower motor turns on when grounding pin 13 on B36

Testing: Remove HVAC control panel. Unplug the 6 pin connector for the fan switch (i15). Insert your negative lead into pin 6 and positive lead into pin 5. You should get 12v.

http://i.imgur.com/qIRqFwZ.jpg

If 12v is detected, set your multimeter to ohm resistance and measure continuity between Pin 6 on i15 and a good ground. Do the same with pin 2 on the 16 pin connector

http://i.imgur.com/HvLZiJV.jpg

and pin 2 (middle) the three pin connector.

 

If resistance is measured on it, then its possible the control panel is fubar.

[doublechaz]

Great writeup!

 

When you are checking connection from the negative side of the fuse to ground, the reading you get should be really low, like 1 ohm or less.

[Setnev]

I usually set it to 10 ohms first and move up from there. Take a piece of test wire and run a dry test first to see what baseline you should use. None of the wires listed are running resistors, so you don't want an accurate reading, just A reading. When the multimeter tests ohms, it puts a small current through the wire and measures the drop from one side to the other. Great for testing negative leads too.

[aormsby]

 

 

 

 

 

 

 

Testing HVAC system:

 

 

 

Condition: SBF-3 tests with 12+ volts with key on, ground connection has continuity, 45A fuse is good. No power to HVAC system

 

 

 

Testing: Pull fuse 15 in the interior fuse box. Check continuity of fuse and for contact corrosion. If continuity and corrosion check passes, probe the fuse panel contacts for fuse 15. Check for 12+ volts on the positive side with the key on, engine off. If 12+ V are showing, connection between SBF-3 and Fuse 15 is good on the power side. Switch your voltmeter to measure Ohms resistance. Probe the negative side of the fuse with your positive lead in the fuse connector and the negative lead to a clean body ground. If it registers a reading, ground connection is good. Repeat for fuse 20 & 21.

 

 

First off I want to say fantastic write up and once again thanks for your help.

 

So here's where I'm at: fuse 15 was completely fine both sides measured correctly. For both 20 and 21 positive side measures 12V, but I get no reading on the negative side.

 

So somewhere there's a bad ground. Just to be safe I have already cleaned up GB-1 though 6 in the engine bay. The two ground points that would make sense as the problem ones are are the two on the transmission tunnel (GB-7 and GR). I have cleaned these up as well.

 

 

 

Now here is the development:

 

The radio has started to work intermittently. It came on yesterday and worked normally for the most part, but on a drive last night (I mention night because the headlights were on) the radio would cut out every time I touched the brakes. So triggering the brake lights overwhelmed something. In addition as I'm writing this up I'm sitting in the car with the key set to on. The radio came on normally and without me touching anything shuts off randomly.

 

 

 

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[Setnev]

First off I want to say fantastic write up and once again thanks for your help.

 

So here's where I'm at: fuse 15 was completely fine both sides measured correctly. For both 20 and 21 positive side measures 12V, but I get no reading on the negative side.

 

So somewhere there's a bad ground. Just to be safe I have already cleaned up GB-1 though 6 in the engine bay. The two ground points that would make sense as the problem ones are are the two on the transmission tunnel (GB-7 and GR). I have cleaned these up as well.

 

 

 

Now here is the development:

 

The radio has started to work intermittently. It came on yesterday and worked normally for the most part, but on a drive last night (I mention night because the headlights were on) the radio would cut out every time I touched the brakes. So triggering the brake lights overwhelmed something. In addition as I'm writing this up I'm sitting in the car with the key set to on. The radio came on normally and without me touching anything shuts off randomly.

 

I'm glad to hear something is working out with it and you're starting to get it worked out.

 

Fuse 20 & 21 on the negative side terminate at the Blower Motor Relay. You won't get any reading on the negative side of fuses 20/21 if the relay is in the off position. I forgot to mention that. But we should test that circuit anyway.

 

There are two connectors that are for the blower motor relay, B51 and B50. B51 is the gray 11 pin pin connector should be located above the interior fuse box. Pin 9, is a red/yellow wire that leads to the negative side of fuse 20 and 21. Test continuity to the female (the part the connector plugs into) to the fuse leads you got no reading on.

 

Then, find the Blower Motor Relay (B50). It is a blue 4 pin connector right above the B51 connector. It's going to be WAY up under the dash, almost right behind your mirror controls (ironically, your horn relay, a 3 pin connector is right under it). Test the continuity of Pin 2 (upper right pin when looking at the connector with the lock up. Test continuity between B51 pin 9 and B50 pin 2. The wire color is still red/yellow on B50, so that's how you know its right.

 

While your probing the wire from the fuse box, test the relay for safe measures. To test it, take your multimeter set to Ohms and probe pins 1 and 3 on the relay itself. If the reading is 0, the relay is bad. Replace the relay and try again. If the relay is good, the problem lies between the HVAC control panel and the relay, which you should continue troubleshooting on the list I gave you.

 

Sorry that this is pretty lengthy, but it's all for piece of mind in the name of troubleshooting. You don't want to start replacing potentially expensive relays, switches, and control panels until you know for a fact that the wiring doesn't have a short, which is why we're testing from the main power line back to the individual components. This is the way I troubleshoot electrical systems and how I was able to determine my knock sensor was bad, when everyone said it wasn't.

 

As far as the radio goes, you definitely have a short in that system, most likely the grounding system for it, but it could be a dead short or crossed wires after the fuse panel on the 12v side which may not blow a fuse, but will cause weird anomalies.

[Setnev]

Any updates on the testing?