Author Topic: Temp/Oil Gauge and Tach ?  (Read 19157 times)

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Offline mikeb78ta

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Temp/Oil Gauge and Tach ?
« on: February 12, 2009, 09:42:04 PM »
Hey Guys,
Here we go again... I have read almost every thread regarding this much discussed topic. My questions are as follows

Temp/Oil Gauge
1. Neither of these work. I have checked as stated on many threads to move the wires from the senders and ground them.  They do nothing when I do that they don't move at all.
2. There is voltage to the oil press. sender wire with the key on.  Nothing happens on the gauge however.  Not sure what else to do.
3. There is no voltage to the Temp wire??

Tach
1. I read that the tach connects to the distributor but should there be voltage to the 2 wires that goes to the tach at the dash with the key turned over??(pink/White)
2. which wire is for the tach at the distributor?

I went ahead and bought a new Printed Circuit from Ames. It should be here in a few days,but if its not that what else should I look for?

Thanks,
Mike

1978 Trans Am 403 WS6, BLack, Camel Deluxe Interior

Offline ta78w72

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Re: Temp/Oil Gauge and Tach ?
« Reply #1 on: February 12, 2009, 10:24:50 PM »
DId your order the right circuit?  There are two versions for 78.

On the Temp/oil pressure:  pull the cluster and with the key on measure for voltage at pin number five of the white cluster connector (a pink wire).  That should have voltage.  My guess is you have a break in the plastic film circuit near the top of that line where it bends.  It gets really thin at that point and that's where they tend to break.  You're on the right track with a new plastic film circuit.

The tach is fed from a pink wire that comes out of the fuse box.  That line usually has a fuse connector in it.  Check the fuse.

Offline mikeb78ta

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Re: Temp/Oil Gauge and Tach ?
« Reply #2 on: February 12, 2009, 10:38:50 PM »
I hope I ordered the right one.  I called in the order and spoke with someone.  What is the difference? As far as the Tach goes where is the Fuse located?  I had the steeing column unbolted and the cluster out today.  I didn't see an inline fuse.  Where is it located?
1978 Trans Am 403 WS6, BLack, Camel Deluxe Interior

Offline mikeb78ta

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Re: Temp/Oil Gauge and Tach ?
« Reply #3 on: February 13, 2009, 10:39:26 AM »
Any other Suggestions?  I went down to my car this morning and there isn't a fuse, but even more strange is that I only have 10.5 volts coming out of the pink wire feed.  Could that be part of the reason my tach isn't working??
1978 Trans Am 403 WS6, BLack, Camel Deluxe Interior

Offline ta78w72

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Re: Temp/Oil Gauge and Tach ?
« Reply #4 on: February 13, 2009, 11:33:11 AM »
On the circuit, it depends when your car was assembled.  Earlier ones got a round tach cover on the back and later ones got a rectangular one.  Thus, the physical dimension of the circuit assemblies are different and not interchangeable.  The electronics are the same though.  What exactly did you talk about with that guy?  If he asked you the VIN or build date, chances are you'll get the right one.  If he asked you whether or not you had rally gauges....it's 50/50.  You'll know as soon as you see the circuit and look at your old one.

On the tach if you disconnected that pink line and measured the voltage....10.5 should be enough.  The fuse is located on the pink wire.  The fuse holder has the pink wire on either side.  The fuse holder should be white.  But if you're getting voltage with that wire disconnected the fuse should be OK.

Then you need to see if you're getting a signal from the distributor.  There is a tab marked "tach" on the lip on the distributor where the feed wires come in.  You'll need to consult with the service manual for the specifics...but you connect a light bulb to that wire with a probe....then at the RPM's go up...the light bulb gets dimmer.  That means you're getting the right signal to the tach.  A strange test...but that's what the service manual says to do.  I guess you'd need a scope to really see the signal.

Does your tach just sit idle?  Are both the brown and pink wires connected?  The brown wire comes from the tach...although I think that wire changes color after exiting the firewall towards the distributor.
« Last Edit: February 13, 2009, 11:40:33 AM by ta78w72 »

Offline mikeb78ta

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Re: Temp/Oil Gauge and Tach ?
« Reply #5 on: February 13, 2009, 12:42:28 PM »
Regarding the Printed Circuit, I will call Ames Today to make sure they send the right one.  I did tell him that the The car has rally gauges, however he didn't ask anything else.  I will confirm that I get the round back circuit. 

Regarding the pink wires I found some pictures on the forum regarding the pigtail that comes off the fuse box. at both pink pigtails there is voltage.  The brown wire to the distibutor is connected.  I will try the light bulb test with the car running to check if anything happens.  Also the 2 wires (pink/white) at the Tach itself are both there.  I also purchased another Tach it also doesn't work so I ruled out that there was  a possibility that the Tach is Bad.

Should I try to run a ground via a jumper to the back of the Tach and a good ground spot to see if there is a ground issue?

I guess I'm just running out of ideas.  Thanks for the help

Is it possible that the brown wire that connects to the distributor may not be connected under the distributor cap?
By the way there definitely is no "inline Fuse" anywhere on the pink line or the brown to the distributor under the hood.  I traced it from the tach harness at the dash to the fuse box???
1978 Trans Am 403 WS6, BLack, Camel Deluxe Interior

Offline ta78w72

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Re: Temp/Oil Gauge and Tach ?
« Reply #6 on: February 13, 2009, 02:20:49 PM »
Well, I guess some of the pink tach wires had a fuse and some didn't.  But after all these years you might not have the original wire anyway.

On the plastic circuit, tell ames you need the early 78 circuit (if you have the round tach plastic housing).

On the tach, yeah, it's possible you've got a back coil lead.  Try the light bulb thing to see if your getting a signal.  I'm not sure what a volt meter would tell you.  The service manual doesn't suggest using one.....at least not that I could find.

If you haven't done a tune up, you could pull the cap and rotor and change them.  And, also pop in a new coil and module.  I do that every ten years or so to avoid getting stuck.  The cap and rotor on my daughter's car gets replaced every two years....just before I get the car smogged.  The coil and module ten years is about right unless you put lots of miles on the car.

The other thing to do is to trace that tach wire from the distributor to the tach just to make sure there aren't any breaks.  Also, if you pull that connector off the tach.....don't break the ears....I hate that!!!  When I see those connectors at the salvage yard I cut them off and bring them home. 
« Last Edit: February 13, 2009, 02:22:53 PM by ta78w72 »

Offline mikeb78ta

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Re: Temp/Oil Gauge and Tach ?
« Reply #7 on: February 13, 2009, 02:38:41 PM »
I had the car tuned up right after I bought the car 4 months ago.  Would they have automatically changed the coil and module?  The cap I know for sure is new. Delco.  The rest I will try and get back to you. Is it possible there is no contact to the brown tach wire and its not getting signal?  I'll try the light bulb trick, if nothing maybe there isn't contact???

I spoke with Ames and they said they only have a rally gauge and a non rally gauge circuit??? I will have to wait and see.  I did tell them I need the Round Opening.  We'll just have to wait and see.  I'll keep you posted to let you know my progress.  Something eventually has to come of this.. As always, thanks a lot for taking the time to walk me through this. 
1978 Trans Am 403 WS6, BLack, Camel Deluxe Interior

Offline ta78w72

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Re: Temp/Oil Gauge and Tach ?
« Reply #8 on: February 13, 2009, 05:26:12 PM »
I had the car tuned up right after I bought the car 4 months ago.  Would they have automatically changed the coil and module?  The cap I know for sure is new. Delco.  The rest I will try and get back to you. Is it possible there is no contact to the brown tach wire and its not getting signal?  I'll try the light bulb trick, if nothing maybe there isn't contact???

I spoke with Ames and they said they only have a rally gauge and a non rally gauge circuit??? I will have to wait and see.  I did tell them I need the Round Opening.  We'll just have to wait and see.  I'll keep you posted to let you know my progress.  Something eventually has to come of this.. As always, thanks a lot for taking the time to walk me through this. 

When they installed the coil in the cap, they could have screwed up that tach wire...but check with the light bulb.

Ask Ames if the 77 circuit is the same part number as the 78 they are sending you.  77 should be the same part number as your 78.  The later 78 circuits are the same as 79.

Ames doesn't know these cars like we do.

Offline mikeb78ta

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Re: Temp/Oil Gauge and Tach ?
« Reply #9 on: February 13, 2009, 05:45:35 PM »
I will check with Ames on the circuit.

One big thing I forgot to do when I hooked up the secondary Tach I have is to Gound It to the Chasis.  I Did that to both Tachs I have.  When I did it to the Tach that is on my car still nothing.  When I did it to the secondary one it pegged it to 6000 and it stayed there. 

I also took a lead and a Light bulb (12 volt car bulb) and hooked it up to the tach port on the distibutor Nothing happened. Am I getting any closer to the elusive Tach?  I'm not sure...
1978 Trans Am 403 WS6, BLack, Camel Deluxe Interior

Offline ta78w72

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Re: Temp/Oil Gauge and Tach ?
« Reply #10 on: February 13, 2009, 06:36:18 PM »
I will check with Ames on the circuit.

One big thing I forgot to do when I hooked up the secondary Tach I have is to Gound It to the Chasis.  I Did that to both Tachs I have.  When I did it to the Tach that is on my car still nothing.  When I did it to the secondary one it pegged it to 6000 and it stayed there. 

I also took a lead and a Light bulb (12 volt car bulb) and hooked it up to the tach port on the distibutor Nothing happened. Am I getting any closer to the elusive Tach?  I'm not sure...

It's the signal from the coil.  remove the top off the distributor cap and check the wires.  Those wires are really thin and it could have broke.  Also, they may not have it wired correctly.  I don't remember off the top of my head the color wire combination and where they go.  I always write it down before removing the old coil though.  I bet they switched some wires.

Offline mikeb78ta

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Re: Temp/Oil Gauge and Tach ?
« Reply #11 on: February 13, 2009, 06:53:53 PM »
I have read up a little on the distributor.  Is there anything in particular I should be careful of. I don't want to put anything out of order.  Should I leave the - terminal on the battery or not?  Sorry first time messing with the distributor. Thanks
1978 Trans Am 403 WS6, BLack, Camel Deluxe Interior

Offline mikeb78ta

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Re: Temp/Oil Gauge and Tach ?
« Reply #12 on: February 13, 2009, 06:58:29 PM »
Oh Yeah 1 other thing does that mean that my original Tach is Bad? that one didn't do anything.  Is the one that pegged potentially good?
1978 Trans Am 403 WS6, BLack, Camel Deluxe Interior

Offline ta78w72

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Re: Temp/Oil Gauge and Tach ?
« Reply #13 on: February 13, 2009, 07:15:44 PM »
I'm not sure if your tach is bad or not.  My guess is it's good.  I always assume the gauges are good until I prove them bad.

You need to pull the cap.  What I do....it's hoky....but I've been doing it the same way for lots and lots of years....I start with one plug wire...mark it number one with some masking tape.  Then pull the wire around counter clockwise giving them the next number.  I don't worry about the cylinder number...just how I pull them out.  It's the way a moron does it.   ;D

Then there are four spring clips that you can release with your fingers.  Then disconnect the connectors and pull the cap off.  Be careful with those connectors because the ears break very easily...so don't pry them open or you'll break them.  I've never broke one but my daughters T/A had a broken one when she bought it but I had a spare.

There's a lid on top of the cap that's held with some fasteners.  Remove the fasteners and you'll see the coil and the wires coming out from it and into that lip on the cap.  Post a picture when you get there and we'll be able to see if it's connected properly.

You don't need to disconnect the battery...just make sure the ignition is off with they key out.

Good luck!

Offline mikeb78ta

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Re: Temp/Oil Gauge and Tach ?
« Reply #14 on: February 13, 2009, 07:20:15 PM »
Thanks so much for sticking with me through this.  I feel like I'm getting closer.  I will send pics tomorrow when I remove the cap. Much appreciated...
1978 Trans Am 403 WS6, BLack, Camel Deluxe Interior