Just curious, have you tried taking a resistance reading with the bulbs removed? Working with 0.8 ohms, it would be impossible to tell if there were other contributing factors.
I know what you mean about the low resistance reading @OldcarsRbest. I have eliminated the trouble being with any of the rear lights by removing them one at a time from the circuit at the splice point in the rear area of the van. To me the problem is now starting to look like it may be within one of the two modules the brake circuit supplies power to, and not with the lights or within the wiring harness itself.
The two modules that are tied to the brake light circuit are the front controller module and the anti-brake controller. Even though I have the service manual I still donât know what the front controller module does and service manual doesnât say much about it. I wish there was an easy way to remove the wire going to each of the modules so I could try eliminating them one at a time but I donât know where the wiring splits off from the brake switch and connects to those things. I absolutely hate just cutting into the middle of wires to isolate things but I may be forced to do that.
Last night I got a little drastic since this issue is taking so much of my time. I decided to do what I never advise others doing. I increased the fuse size from 20 amps to 25 amps. After installing the fuse I did a little test drive last night and so far the fuse has held. I was able to go a ways with normal fuse also but at some point in the drive the fuse would always blow out. I will see what this fuse does. If it holds up then I have to think my issue isnât a shorting problem but something is causing more current to flow than it should be normally. I am going to start checking the current flow to lights and other things. I donât know why the brake circuit needs so much current. I estimate the lights use about 5 to 6 amps so I have to ask what else would require so much more current to account for the rest of the current flow?
Thanks for the help and suggestions all and if you think of something more please let me know. I will keep posting updates on this.
I donât know if there are any âclamp onâ ammeters for DC available anywhere - this was dads and is probably 50 years old. Iâd like to see the normal current draw in that circuit, but itâs probably too much for the average VOM. If you could rig up something, you might be able to narrow it down a little further. Even a panel mount DC meter capable of 0 - 50 Amps although it would take some jerry rigging.
A fox and hound tester can help you trace where the wires go. It puts a tone on the lead wires and you run the hound sensor around to find where the wiring goes. Very helpful if you do not have manuals or donât want to disassemble a bunch of stuff to figure out where the wire runs are located.
Any chance you can post the schematic of the distribution of this wire showing everything it feeds?
BTW, you may consider installing a resettable fuse. They have them at the parts store right next to the fuses. Then place your DVM in line with the affected circuit to see what the current draw really is. If DVM limited, use a power resistor as a shunt.
There are lots of clamp on ammeters available. But read the specs carefully, many only read AC current.
Here is one for $40 at amazon that reads up to 400amps DC:
https://www.amazon.com/Auto-ranging-Multimeter-Resistance-Capacitance-Frequency/dp/B01N014USE/ref=sr_1_10?ie=UTF8&qid=1486057972&sr=8-10&keywords=dc+clamp+on+ammeter
A little more elaborate than you need, but some searching may turn up a better choice.
You guys are right on track about checking the current and the choice of testers. I do have a Fluke DC clamp on that I have had for many years and thought about dragging it out. Yesterday I decided to order one of these so I could monitor the circuit while driving around, you can monitor the voltage and current at the same time:
There are a lot of these type of meters for sale but you have to be careful when ordering one. Most of the meters being sold on Ebay require the current shunt to be placed in the return side of the circuit. If you use the positive side of the circuit it will burn out the meter. This unit can apparently be installed on either side of the load.
According to my manual the brake circuit connects to a couple of modules besides the lights. I still have to wonder what is causing the extra high current flow. One would think the lights would be the highest load demand. So far, the 25 amp fuse has held up and I went much further in my driving distance than when I had the normal 20 amp fuse in place. It looks to me this fuse will work out so I can at least get around with the brake lights working.
I would really like to know what is causing the extra current draw. The YouTube video I found earlier that seemed to match my issue exactly was interesting. While he claimed in the video that replacing the brake switch fixed his problem, there is mention in the comments later on that he replaced the fuse to a 25 amp, so I am thinking we have the same issue, and it may be an electronic issue. I wish I knew what the normal draw should be for the circuit. The 20 amp fuse worked for a lot of years. I suppose there could be a leaky electrolytic capacitor in one of the modules causing the problem. After 15 years of service that kind of thing is a pretty good possibility and explanation for the trouble.
Looks like that should get you on the right track.
Iâve had issues with dual filament bulbs anywhere from the filaments touching each other intermittently to an errant strand of wire inside the socket shorting to the ground or turn wires with the right bump or body flex. Yours seems to be north of the rear end, and as you suspect, could be a module.
Iâll keep my fingers crossed for you!
Thanks @OldcarsRbest. I will keep updating the progress on this. Hopefully we will get some sort of good answer to the cause of this trouble that may help someone else later on.
If anyone can tell me what the front control module, which is located in front of the IPA fuse panel, does in this '02 Chrysler T&C minivan please let me know. The info in the manual I have seen so far says very little about itâŠWell after just looking at the manual again there is a whole page dedicated to the connector and description of each of the 49 pins that connect to the module. The module ties to a lot of things in the car. Pin 44 is for the brake switch input but what that input is used for isnât real clear, to me at least. Once I get the current tester I may isolate that lead and then see what the current does.
Here is the latest news on the problem. The 25 amp fuse which worked for a while now blows out also. I stepped it up to a 30 amp fuse (I must be getting desperate). With that fuse in place, and using the small monitor light so I can watch the brake light action while I am driving, things are different. Now when the short happens the fuse doesnât blow out and the monitor light still glows but is pretty dim due to the voltage drop on the circuit due to the high load current. I know if I keep this up I will damage the wiring.
I have decided to cut into the brake light wiring after the switch and run a temporary wire to the rear lights until the problem can be found so at least the rear lights will work. I will also run another wire to the fault wire connection and install a separate brake light bulb in series with that wire from the brake switch. That way when the short happens the current will be limited to about 2 amps and wonât damage any of the wiring and I will also know when the problem is occurring. As of now the problem is very intermittent.
I got out my Fluke Y8100 current probe which I havenât used in years and checked the current at the fuse connection. The meter showed about 5.8 amps of current. Just about what I thought the current draw for just the lights should be. I canât leave the probe in place to monitor the circuit while driving around as it is a little too big. When I get the other one I ordered I will be able to monitor things while driving.
Seems like you are doing all the right things. The series bulb is a great idea.
Your problem reminded me of a problem that I had on a 1985 Ford Tempo that I purchased brand new. After I had owned the car about 6 months, the fuse to the tail lights and instrument panel blew. I replaced the fuse and a week later, the fuse blew again. After the fuse blew the second time, o I took it to the Ford dealer because the car was still under warranty. It turned out that one option on the Tempo that I didnât have was a tail light monitor that would light an indicator on the dashboard. There was a slip up on the assembly line and the tail lights were connected to the thin gauge wire that was for the indicator monitor. After 6 months the insulation burned off the wire. When I would.go around the corner, the wire with the melted insulation would make contact with the body and blow the fuse. In your situation, I wonder if there is someplace the wire to the tail lights makes contact with the body when the car is in motion. You might try holding the pedal down for a couple of minutes while the car is standing still. If the fuse doesnât blow, I would bet on a bare spot someplace in the wire.
If the fuse does blow after holding down the brake pedal it sounds like the situation I had on my first carâa 1947 Pontiac. The fuse for the brake lights would blow if I had to hold.down the brake pedal for more than a few seconds. I traced the problem to the brake light switch. The switch was a pressure switch that was.mounted on the master cylinder. It was defective and would direct the current through the master cylinder to the chassis of the car. Is it possible that there is a path through the brake light switch to the chassis of the car?
One final thought-- the cruise control turns off when you step on the brake. Is there a way you could disconnect the cruise control control in case somehow this is causing your brake light fuse to go?
Thanks for the info guys. Today I really got after the issue and made some changes to the brake light wire. I was able to remove the terminal for the brake lights at the switch to isolate it. I also ran a new temporary wire to the wires going to the individual brake lights and connected it to the switch. To that I also added a test light bulb. So the original wires are now isolated from power except the power that passes through my added brake light that is in series with the problem wiring. When the short happens again the brake filament will turn on but now no more than a couple of amps can flow even if there is a dead short to ground happening. I tied the running light filament of the test bulb to the brake line just so I could also verify power is getting to the brake lights. I did some running around today with the original wiring isolated and the new wire going to the lights and the 20 amp fuse had no problem with that.
The original wiring goes into a large harness that runs behind the emergency brake mechanism. The trouble may be there. The harness then goes down along the floor near the driverâs door in a plastic channel. There practically no way any damage could occur to the wiring inside that channel. I was impressed with the engineering design.
@Triedaq:
The brake switch case is totally made of plastic. There are 3 switches inside it. My manual shows the brake line lead ties to the lights and along with two electronic modules. Both of the modules are located in the engine compartment. It sure would make things easier to locate the trouble if the problem wasnât so intermittent. Perhaps tapping on suspected areas using a plastic or rubber hammer may show up the culprit.
Good stories about the Ford and Pontiac issues.