Elec. problems 74 Dart

[big&bad]

Hi @ all...

My project is terrorising me...

The car is allmost done - and thanks to FABO I could fix a lot of problems, but today we noticed two new ones...

Problem 1: the stop-lights aren't working. I don't know if we've done something wrong while wiring, we checked it twice, but we can't find the cause. We replaced the stop-light-switch, controlled the plugs and sockets - nothing... Any idea? Maybe a relay? It's my first american car, so I'm really helpless...

Problem 2: the temperature-gauge isn't working. We checked the fuses, replaced the sensor, nothing helps. Here too: Any idea? Maybe the gauge itself? And if it is broken - where to get a new one and how to replace it?

Thx...

 

[67Dart273]

Stoplights..........most all stoplights on U.S. cars of that era went through the turn signal switch.

So check right at the stoplight switch or at the turn signal switch connector

If you are getting stoplight power there, going INTO the switch, AND if the turn signals function, then it's a problem in the column signal switch.

Temp.........Does the fuel gauge work?

Did you try shorting the sender wire to ground with key "in run" and see if the gauge deflects?

If the fuel gauge works, possible problems are.....

Broken connector (insided) the molded sender connector

Corrosion / loose in bulkhead connector

Poor connection at the instrument cluster PC board pins and harness connector

Loose / corroded stud / nuts on the gauge to panel

If the fuel gauge does NOT work this could get deeper

 

[BillGrissom]

I have two 80's German cars (M-B 300D) and the stop lights and temp sensor are essentially the same as in my 60's Mopars as I recall. The main problem is that your approach seems to be "throwing parts at the problem".

You need to get a wiring schematic (many posted here). If you had one, you wouldn't wonder if there is a relay in the stop light circuit. You also need basic tools like a multimeter.

I agree that routing the stop lights thru the turn signal switch is confusing and causes problems. Not all cars had that, just later ones where they decided to share the same rear filament for both turn signal and stop (a styling choice).

The temp sensor function (and fuel level) can be checked by replacing each with a resistor to ground (or simply short to gnd). The 5V regulator that plugs into the instrument cluster if often the problem, and there are many posts on this and how to improve it cheaply.

As an example of trouble-shooting, two electric windows in my 85 M-B recently stopped working. I first tried swapping the switches in the console (no change), then measured the voltages while actuating. In both bad ones, the 12 V source dropped to <1 V while trying to actuate the window. The schematic showed that they shared a common fuse, which couldn't be blown since it fed 12 V when the switch was off. I then knew there was excessive resistance in the supply wiring. I pulled the fuse (pain on this car). It looked fine, but I sanded the ends and the clips in the box, re-installed w/ silicone grease coating, and the windows worked fine. Surprising, since I didn't see any corrosion at all. A few weeks later, before my son took the car away, I found the sun roof stopped working. Sanded that fuse and it then worked. A shop might have charged me for new window regulators, switches, who knows what. I recall as a kid, driving in our Matador station wagon in Florida for maybe 5 summers with no AC, because the blower stopped. My dad had pulled the blower fuse and it looked OK so he put it back and gave up. He didn't see that the fuse wire had melted right at the cap, due to heat from resistance at the clip. Had my dad pushed on to find root cause (or even swapped fuses), we wouldn't have suffered for years. Most people are like my dad, you need to train yourself to be better.

 

[airgrabber]

Good grounds for the stop lights? There should be no relays involved. All that wiring usually runs inside the car too, so less chance of issues like under the hood. I'd trace back from the stop light bulb sockets and find the grounding mechanism. Some ground right to the metal housing, others have a separate ground wire. Also, use a volt/ohm meter to see if electricity is making it thru the wiring all the way to the bulb when applying the brakes. Lastly, check for a broken wire/open circuit between the switch and the bulbs - simple continuity test from the switch to the bulb.
Temp gauge - sending unit is easy to replace, it's on the motor, purple wire slips over a threaded stud on the sending unit. Purple wire goes thru wiring harness to firewall to a connecter leading to the gauge or a pin on a pc board. Check for continuity from sending unit to endpoint of harness. Gauge could be bad, or printed circuit board that gauge connects to could be corroded under the sheet metal nuts that hold the gauge to the pc board. Scotch brite/400 sandpaper to lightly clean copper contacts. Replacement gauge thru parts wanted here on this board.