Hitman's Pontiac Trans Am Forum

Trans Am Information => Trans Am Tech => Electrical => Topic started by: bandit79mpr on January 10, 2010, 08:35:13 PM

Title: gauges stuck after storage! *problem solved*
Post by: bandit79mpr on January 10, 2010, 08:35:13 PM
i have a 79 trans am that i bought from the origional owner in 1996 , i drove the car for a few years and then put it in storage because i really did'nt want my girlfriend  to drive it anymore AFTER she hit a deer with it and destroyed the grilles and bezels. anyhow, i have been starting the car a few times a year and washing it as needed then putting it back in the garage, my problem is that the gauges all seem to be stuck at the point they were when i shut the car down last time, the tach is on 800 rpms and will not not go below that point but works normally above that, the temp is stuck on 160, the oil pressure is on 40. all the gauges function properly ABOVE the mentioned settings, but the needles will not fall below that point. did moisture make the needles stick? it's like they are frozen in time and it really bugs me. the car is in awesome origional shape and i plan on registering it this summer after some new hoses and such and enjoying it instead of looking at it getting dusty. has anyone else had this happen? is there a way to fix it without tearing the dash apart? please help me!!!!!
Title: Re: gauges stuck after storage! help me!
Post by: Rick on January 12, 2010, 11:29:11 PM
Welcome to 78TA!

You might try forcing the gauges to their extremes a couple of times by manipulating the inputs -- it's easy enough to do.  The sending units on these things work by providing the resistance for the actual gauge -- the gauges run on current.  One side of the gauge is tied to the +12 VDC in the dash, and the sending units vary with resistance so that open (no current) makes the gauges read full high, and no resistance (max current) makes them read 0.  It sounds like maybe there's a bit of corrosion in the needle movements, so maybe if you ground the sending unit end of the wire out a couple of times you can break it free.  Locate the sending units on the engine, and use a jumper to ground them out to either the block or directly to the (-) terminal on the battery.

If you don't have one already, you should get a factory service manual.  Those have all the wiring diagrams in them, so they are invaluable for this kind of work.  I wouldn't be without one because you have no idea of what's going on with the car.  Hitman sells them here on the main site (78TA.com) on CDROM in PDF (Adobe Acrobat) format.  Best money you'll spend on one of these cars!

Good luck, and let us know how it comes out! ;)
Title: Re: gauges stuck after storage! help me!
Post by: ta78w72 on January 13, 2010, 09:37:07 AM
Just disconnect the lead from the sending unit.  For the temp gauge, with the key on, ground the lead and the gauge should register far to the right.  With the lead hanging, it should register way left.  Oil pressure gauge works just the opposite.  If they don't do that, you've got to replace the gauges.

On the tach, they don't necessarily go back to zero.  If it works correctly with the engine running you're OK.  But if it doesn't.....do what Rick suggests. 
Title: Re: gauges stuck after storage! help me!
Post by: bandit79mpr on February 01, 2010, 07:25:52 PM
ok, let me just say that you guys rock! manipulating the gauges manually got everything working smoothly again. i thought for sure i was going to have to buy new ones, thank you for the sound advice and for saving me a heap of cash!
Title: Re: gauges stuck after storage! *problem solved*
Post by: jphillips3333 on February 01, 2010, 07:54:29 PM
Where's the pix?