31rx7

I have been casually chasing the following problem for about a year now, but it's time to get serious. The car is a 1985 GS, manual trans, 164k miles.

The following problem occurs intermittently: When pressing on the brake, the lights for gauges in the main cluster come on faintly (Speedo, Tach, fuel tank, etc.). When I say "faintly", I mean maybe 25% of full illumination. The rear defroster indicator light comes on almost full brightness, as if the defroster is on. The "Stop Light" indicator comes on full brightness. The turn signal indicators both come on faintly (25%). The rear brake lights come on at partial (25%) brightness (less than the parking lights), and both rear turn signal lights and read side indicator lights come on at partial brightness.

This happens whether the engine is running or not, and whether the headlights are on or not. If the engine is running, the "Stop Light" indicator usually stays on and the above condition persists until you go over a bump in the road or something.

While this is all happening, the front headlights, turn signals, parking lights, and side indicator lights are unaffected and function as designed.

It also keeps blowing the interior light (dome light) fuse; I am trying to find the pattern for this. The other fuses are fine.

Finally, if the engine is off and the key is out, there is a slight clicking noise coming from under the dash when you press on the brake.

Everything else is functional as far as I can tell.

The intermittent part of all this is that it happens about 60% of the time, seems to come and go with no pattern, except that when it happens, it occurs for a while (maybe a few minutes) then goes away for a while and comes back. No pattern to the frequency; I even went so far as to try and time it!

I have changed combination switches, inspected the wiring in the steering column, swapped brake light switches (the one on the pedal), and have not located the problem.

It seems to be related to something in the rear wiring harness, specifically the lighting circuit. It is also an unswitched circuit that is live all the time.

I am planning to pull up the carpet and panels to do a visual inspection. Next step is to start some analysis by disconnecting various parts of the wiring harness (particularly the rear harness and door switches) to see if the problem can be isolated to a specific connector or section of the wiring.

Any ideas on where to look or how to diagnose would be appreciated. I have limited electrical expertise, but am reading to learn!

enigma32

hmmm
I would suspect there's a funky ground... and that your plans to go through piece by piece and check it out are probably the easiest way short of spending a bunch of time looking at the wiring diagram... :-)

If it happens with the brakelight I would check the grounds (and possibly the bulbs) involved with the brakelights first

Anex 570

This is a bad ground, I repeat, bad ground. I know for 100% that it is because I spent about 6 months on my own trying to figure it out, and had a car guy buddy just get it done in about an hour. You do need to look at the all the connectors for the lights and clean them. Check around the stupid headlight motors for black wires that just bolt down to the chassis under the motor. Clean them!!! Clean the hell out of your battery cables and follow them on both ends! You HAVE to do atleast what I told you, then get your manual and just study the wire diagram for the tail lights. Theres not really a whole lot there, you just have to double check everything, because its so easily over-looked. I hope you can get this done fast then I did. I repeat, everything I mentioned above HAS to be done or you wont get anywhere at all. I know for damn sure...

31rx7

I will check the grounds and inspect the lights and sockets. However, I would think that if it was a bad ground that it would cause an incomplete circuit, thus rendering the circuit in question inoperable.

The symptoms described to me imply a short across across circuits. This could be due to a host of things; again, I need to get serious about inspection to find it.

darkfrost

iTrader: (1)

There could be other problems involved, but start with the grounds. You would not believe the amount of things a bad ground can make weird.

Anex 570

The short across circuits your talking about is from bad grounding. It really is messed up how it happens on these cars... I've never had a problem like it before on anything..

GavinJuice

Just replace your battery wires period. Add another ground to the frame seen as how the factory wire was t'ed off to the frame also.

31rx7

Thanks. Will report progress later.

31rx7

OK. I believe I have the problem 90% fixed; the remaining 10% should be relatively easy.

I started first with a visual inspection of the wiring and connectors on the rear harness. Did not find anything particularly out of order. I then noticed the dome light (the one switched by the doors being open) and map light did not work under any conditions. Fuses were all good. I took out the dome light / rear view mirror assembly, and behold one of the ground wires for the dome light was not soldered on, and the clip that holds the dome light in place on the hot side was un-soldered.

For kicks, I removed the entire assembly, covered the hot lead, and behold, no problems with dim dash lights or anything. The wiring on the dome light assembly looks like it was repaired once already so I will probably just go get a spare somewhere and put it in.

I still have an intermittent problem with the "Stop Light" indicator coming on, which I suspect is a poort ground for one of the brake lights or running lights.

Thanks for all your help and suggestions.

partsguy74

Grounds are weird.. I had a bad ground on one of my old Monte Carlo's.. Every time I turned my left turn signal on, my right headlight would blink..

LongDuck

When your 'stop light' indicator comes on this is due to a couple of minor, but easy to fix, items. Easiest things first; (assuming that the 'Stop Light' indicator is coming on full-bright, and not dimly, as you mentioned before)

1) check your brake fluid - when the brake pads wear, they will require more fluid from the reservoir to displace the brake pistons, thus drawing your brake fluid down. As the fluid draws down, the magnetic switch on the float will activate the 'Brake' light on your dash - the same one used for your handbrake, when engaged.

2) check your tail light bulbs - when a brake light bulb goes out, the 'Brake' light comes on because Mazda built in a resistance checker. This electronic gadget operates the 'Brake' light whenever the lights are turned on and your brake lights aren't drawing the proper current that good, functioning bulbs would require. If the resistance is low because a bulb is burned out, the gadget tells the computer to turn on the light.

Simple fixes that may or may not be related to your previous electrical problems.

For the record, I had the exact same problem with my domelight on my 84SE and fixed it with some small screws and crimp connections for the wiring - fixed it up and working 100% to this day. Good luck,

enigma32

Yeah, definitely check the brake fluid and the taillight bulbs...

Mine did that for a week or so and all I had to do was clean the connectors on the taillights....

glad things seem to be workin' better for ya!