Help needed.

[General Jameson]

1995 Roadmaster

My fuel gauge started freaking out sweeping across to full then rests back to normal fuel level and will occasionally just go to full then sit their. Playing with some wires in the headlight switch had some effects to it also. My door locks constantly try to unlock when the turn signal is on. My brake lights are very dim. Sometimes the turn signals don't even flash just steady on and tail lights are very dim. No brake lights but center high mounted is still lighting up no problem. Doors unlock when you turn on the headlights.


Would all this be a culprit of the headlight switch going bad or bad wiring? I know not all the wires were connected when I bought the car cause someone else had to do some repair work, but I had no problem like this before. When I took the switch out their are some burn marks on the harness, I don't know if this is old or new.

This all started after the car broke down and I found out my cats are backed up and need to be replaced. Pulled out the o2 sensor and the car fired right, up so blocked exhaust. We hooked up a snap-on tool to the OBD could that of somehow shorted something out? I saw no bad fuses.

I am just thinking of going to the junk yard and cutting one out from as far in the dash as possible to match and hook up all the wires.

 

[buickwagon]

Strange effects like you are describing are often the result of ground distribution problems. When power is applied to one circuit but there is no ground or a poor ground, that power may seek ground through other circuits. So for example, if the turn signal shares a poor ground connection other devices, the power may try to back-feed through the associated circuits when the turn signal is activated. I would look very closely at the body grounds for loose or corroded connections. Your burnt harness may also contain damaged insulation -- it would be worthwhile carefully opening the outer covering and examining the inner wires at that location.

I don't see any way the scan tool could have caused this problem. It just doesn't connect to those circuits.

 

[General Jameson]

Well I have found a headlight switch and wiring pigtail brand new and I am going to replace hopefully soon. It looks to me that whoever had it before just used some junk part and wired it up as good as they could which to say was done horribly with exposed wires.

My brake lights also don't go on when pressed just go dark the center high mounted is working just fine though. I am hoping it is just the brake switch?

For the passenger side cat getting a piece of straight pipe should be no problem but the driver side may cause some difficulty. I may just try to hollow them out or something. Thankfully I do not have to pass any emissions tests.

I have some of the dash out and am going to pull the instrument cluster and just look over everything to see if their may be another gremlin hiding. I hate electrical work I would much rather be wrenching and busting knuckles or something than wire hunting. 🙁

 

[buickwagon]

If the centre-mounted brake light works ok, then the brake light switch works ok. Are the bulbs burnt? If not, then I think you are back to investigating grounds.

Electricity has to flow in a circuit. No ground path, no circuit. Most grounds eventually end up involving a screw to the body metal, witch is a great place for corrosion to develop.

 

[MrBuick (Magnum)]

This screams grounding issue. There are 2-3 grounding screws at the point where the body meets the floor by the front of the drivers door. Same at the passengers front door. Remove the trim piece around the hood release cable, then peel the carpet back.

 

[General Jameson]

This screams grounding issue. There are 2-3 grounding screws at the point where the body meets the floor by the front of the drivers door. Same at the passengers front door. Remove the trim piece around the hood release cable, then peel the carpet back.

Will do, thank you!

@buickwagon: No burnt bulbs or anything.

 

[buickwagon]

Get a 20' spool of wire. Connect one end directly to the battery - post. Connect the other end to one of the ground points in the trunk (black wire). Try your brake lights.

 

[ilgoldstein]

Just don't ground the positive terminal or you'll see sparks (and perhaps yourself) fly!

 

[General Jameson]

The grounds by the floor front doors are just fine looking tight and nor rust or anything around them. The harness going to to brake lights in the trunk has had some work done but was wrapped pretty good and all connections were tight and free from corrosion.

Now I saw a wire ran from the radio harness to the headlight switch for god know what I just disconnected it, I honestly have no idea what they hooked that up for. It couldn't be for the lights on the radio as they would come on no matter what with power as it is a aftermarket POS radio.

I had grabbed the headlight switch and it was HOT at the connector. Could this possibly be the source of my problems, just the headlight switch? I found a replacement pigtail and switch I think would work. The one in their now was not original to the car and had extra wires and stuff I believe it came from a car with the twilight sentential headlights or something. Anyway it was a used part when installed by someone.

This is the switch and pigtail I found.

Or possibly the switch is getting hot from a bad wire, short or something somewhere else? I may just end up having to take it in to someone to diagnose the thing.

 

[buickwagon]

The grounds by the floor front doors are just fine looking tight and nor rust or anything around them. The harness going to to brake lights in the trunk has had some work done but was wrapped pretty good and all connections were tight and free from corrosion.

Ok, so the wires are grounded to the body. Possibly, depending on the integrity of the work done in the trunk. "Wrapped" may just be hiding a broken conductor inside, after all. However, how is the body grounded to the battery? Again, run a wire from the negative terminal of the battery to the taillight ground in the trunk and see what happens.

As for your hot headlight connector, I guess the question is "how hot is hot"? Certainly, heat is generated by running current through a resistance. The more current there is, the hotter it will get. So a short-circuit will heat up a connector quickly -- usually hot enough to burn out a wire. There should be a fuse or circuit breaker to protect the wires (in the case of headlights, it's usually a self-resetting circuit breaker, so the headlights repeatedly cycle with the breaker). In fact, a short circuit, or partial short could generate enough current to have burned out a ground wire already. Similarly, the higher the resistance, the hotter it will get.

The headlights draw a fair bit of current under normal conditions, so it doesn't take much corrosion to generate some heat. The dimmer switch that controls the dash light levels is a variable resistor incorporated into the switch so it always gets warm. It might be that you are feeling some of this heat too.

 

[General Jameson]

The connector itself was hot and the wire was warm also not the switch itself, just where it plugs in. It was only on for like 2-3 min. I will have to do the ground for the tail lights in trunk over the weekend. I had unwrapped the work in the trunk to check their work, not all of it but a good portion to where they had bypassed a corroded connector.

Also I turn the headlights on with the car running and it will kill the engine now? I am double thinking that the cats are bad and that maybe I just have a really bad electrical problem. Car will die when I try to drive with lights on or off though. It does idle fine but when gas is applied it will hesitate and just die.

I am just thinking of dumping it off at a shop and letting them sort it out I really don't have the $ though now and would really like to hunt this down. Just aggravating.

Thank you for your replies and help I do appreciate it tremendously.

Edit:The battery is grounded right next to it on the fender wall with a star washer. It is tight and free from rust or corrosion.

 

[buickwagon]

It certainly sounds like somebody has played with your wiring before, so maybe they buggered something up. The engine dieing when you turn on the headlights could be because the ignition system is losing power. Again, it could be a ground issue -- poor grounding eliminating the differential -- or something is drawing so much power as to overload the capacity of the charging system.

The problem with that theory is the alternator should be capable of nearly 100 amps at idle but the headlight circuit should be protected by a fusible link from the U/H electrical centre, a 20 amp fuse in the interior fuse panel and a built-in circuit breaker in the headlamp switch itself. Anything drawing enough power to overwhelm the alternator should be blowing fuses left, right and centre. You could confirm this by unplugging the headlight switch to see if the problems go away.

Do you have a voltmeter? If so, meter the battery voltage with the engine off -- it should be around 12.3v to 12.8v. Now start the car and it should jump to around 13.5v to 14.5v. That would confirm that the alternator is doing it's job. Meter between the alternator case and the battery negative terminal. It should be nearly 0 volts -- any significant voltage there should be impossible since the starter motor is grounded through the engine too. Meter between the battery negative and a clean piece of bare body metal. Again, it should be 0 or you have a bad body ground.

Now, let's check the positive side. Meter from the positive battery post to the post on the passenger fender then between the battery positive and the big wire on the alternator. Finally, check between the battery positive and the bit of exposed metal on one side of the #1 fuse (25 amps) in the underhood fuse block. Again, they should all be not more than a few tenths of a volt above 0. Any significant voltage on any of those indicates a bad wire or connection in the supply or one heck of a current draw.

 

[MrBuick (Magnum)]

Is the Aux battery post's nut tight?

 

[General Jameson]

"Meter from the positive battery post to the post on the passenger fender"


Positive battery post to negative fender post give me 12v. Those was the only one that do not test correctly. I would think though that that should give me voltage though as it is hooked up to the battery like right their.


Unplugging headlight switch did nothing.

Aux battery post is tight.

My hood light was corroded and slightly melted the socked so I just cut it out for now it had no change in my symptoms.


All other voltage tests were just fine. Is it time to take it to the shop?

 

[buickwagon]

"Meter from the positive battery post to the post on the passenger fender"


Positive battery post to negative fender post give me 12v. Those was the only one that do not test correctly. I would think though that that should give me voltage though as it is hooked up to the battery like right their.

I should have been more precise. By "post on the passenger fender" I meant the auxiliary battery post, not the body ground near the battery.

I also meant for the tests, excepting the first check of battery voltage, to be conducted with the engine running so there would be a normal electrical load and charging conditions applied. If you only had 12v between the battery post and a ground point on the fender, then either the engine was off, or there is a problem.

To explain: Voltage = Current times Resistance (V=IR) With everything shut off, there is no current and therefore no voltage drop produced by resistance. The points I suggested were carefully chosen to reveal problems at certain key connections. For example, metering between battery positive and the #1 fuse would reveal corrosion problems with the Auxiliary post connections -- but only if there is current flowing. If there is little resistance, the voltage drop would be minimal and the meter would show very little voltage. If there is some resistance, voltage is lost as current flows through the connection and the meter shows that lost voltage. Actually, while I say "lost" it is not really lost -- the law of conservation of energy tells us that it is converted to heat. That's probably what happened to your hood light -- the connection corroded to the point of great voltage drop through heating, enough heating to melt the plastic.

Similarly, if the current is far higher than the wire size can reasonably carry, the inherent resistance of the wire will result in a voltage loss as well. This can be a sign of a partial short-circuit or overloading of the circuit, and again, pushing all that current through the resistance of the undersized wire will result in converting voltage to heat.

Now, on the other hand, if you did have the engine running at the time of the tests, and metered 13.5v-14.5 volts at the battery but only 12v between the battery positive and the fender, that shows a 1.5v to 2.5 voltage drop between the battery negative and the body -- in other words, you have a bad body ground.

The main ground wire from the battery goes to the engine itself. The engine, in turn, is grounded to the body via a heavy braided wire which (on the 95 RMW anyway) is located at the rear of the right (driver's side) head and connected at it's other end to the firewall. There is another between the frame and the left rear inner fender, but I don't think that's your problem here. If the engine/firewall ground strap is corroded off, then all the current through the body must be carried through that little wire at the fender, which is probably more than it can reasonably handle, resulting in the measured voltage drop.

If you are unsure about the condition of the ground strap, try using a booster cable to temporarily ground the body to the engine. If you are unsure about the condition of the engine ground, connect the booster cable between the engine and the battery itself.

As for taking it to the shop, that is always an option and depends on your personal determination to persevere in this matter vs your need to get this fixed quickly. I am trying to help you diagnose things with readily available tools. I know that if I had your car here in front of me I could speed the process up immeasurably. I have a number of useful tools that you probably don't have but a shop might. On the other hand, just because the shop has the tools, doesn't mean the mechanic knows how to use them properly. Some guys can be great with a wrench but weak on electrical theory. (Geez, that sounds conceited as hell, doesn't it? But it's true nonetheless.)

 

[General Jameson]

Battery positive to back of alternator was giving me a reading of .33v. That was the only place that was giving me a reading of any significance.

 

[General Jameson]

I am gonna take it to the dealership on Monday, it is $80 for electrical diagnosis. I hope whatever it is can be fixed cheap, or i can do it myself for cheap. Cross your fingers and wish me luck so I can get my Roadmaster back on the road, and not break the bank!

 

[ARCStig]

I can tell you, that the dealership will want around $700 for a new sending unit and installation. It is a new, revised design though. 🙂

 

[General Jameson]

I can tell you, that the dealership will want around $700 for a new sending unit and installation. It is a new, revised design though. 🙂

What sending unit exactly? I am right now at $280 just to find the problem.

 

[General Jameson]

Well $600 and I am once again a master of the road. I knew someone had done some electrical work at one time in the past ownership of the car and it just came and bit me in the butt. Multiple shorts to ground and power in the fuel pump & exterior lights systems. Damaged wires in engine compartment also. Rewired fuel pump circuit. Rewired tail lights, brake lights circuits. Cleaned and re-torqued ground straps. I am just glad and so happy it is all over now.

I appreciate everyone trying to help but with so many little things and doing this over a forum it was just not feasible. I don't have to do anything with the catalytic converters all my problems seem to have stemmed from electrical issues.

I got a free car wash out of the deal though, hooray for me!