o.d. switch - oil pressure - brake pedal short

[troy_p]

bizarre electrical problem on my 94 3.8. oil pressure gauge fluctuates wildly and randomly - goes from 0 to normal and lotsa spots in between - has been doing it since i got the car a year ago. no big deal. the o.d. switch works fine, however when it rains (and sometimes when it's dry) it will flicker by itself causing random downshifts and the rest. recently, when it rains a bunch the brake pedal will tie itself into the circuit so when the pedal is depressed, the overdrive status will change (od light will either come on or turn off depending upon its initial state).

long story short, i've got an electrical short and i was wondering if anyone had a clue where to start looking.

thanks in advance.

tp

[97Bird]

Is the oil pressure guage the only guage that fluctuates? For your trouble with the overdrive I would start by checking all the electrical connections at the transmission to be sure they are clean and tight. Also check any connectors in the harness that goes to the transmission.

[troy_p]

thanks for the reply 97 - yup - only the oil pressure fluctuates. electrically, the rest of the car seems fine. it may not be related at all, just seems strange.
however, the brake pedal is definitely intermittently connected to the o.d. lockout circuit somewhere (mostly when it rains hard). you can tap the pedal and alternate the od lockout status. under the car at the tranny seemed like the obvious place to start, however given the brake pedal thing, i'm not so sure anymore. can anyone think of a physical location where this might be tied together? it's gotta be shorted somewhere, right?

[97Bird]

No, I don't believe you have a short. The brake switch is an input to the Powertrain Control Module (PCM) and the OD circuit and light are outputs of the PCM. The PCM should be located behind the pass. side kick panel. The transmission codes might tell you if you have a faulty sensor. Is moisture getting into the area around the PCM? It is possible but unlikely that there is something wrong with the PCM but it still sounds like a connection or sensor problem to me. If all other guages work fine and you don't hear any bad sounds (rapping) coming from the engine when it goes to 0 then try replacing the oil pressure sending unit.

[troy_p]

i guess the pcm is a good place to start. regarding moisture / water - i have had the driver's side floor mat get wet after a good rain 2 or 3 times in the last year - never did figure out how or why since it happens so infrequently. never the passenger side though.

i assume the oil pressure gauge is not reading properly because i have put over 20K in the last year (most of that with the gauge reading nothing) and i doubt any engine would last that long.

i'll probably start digging at it tomorrow nite. thanks for the suggestions.
t