Author Topic: 8K tachometer in 1979 Trans Am.. will clock run with keyed ignition off?  (Read 316 times)

Den455

  • Forum Member
  • *
  • Posts: 5
Hi

So I've succeeded in reparing most all wiring issues in my 1979 trans am ...I run a MSD and have an autometer tach but would like the 8k factory tach to work as well.

What Ive done is use a new circuit board made for the older 8K tach..74-78 board 1st style from firebird central. Everything works great on it.

I see that the tach has 2 pins on it for a harness... one is 12V and another is Tach signal. Dont have my original tach harness, but ive seen on some dash shots a pink wire and white wire that go into the harness above the column .. anyone know exactly what they are?

http://firebirdtransamparts.com/techinfo/harness/harness.htm

To prevent taking everthing apart, I was thinking the 12V pin on tach to Keyed ignition and tach signal straight to MSD which should work....... but i'm thinking this will make the clock only work when the ignition is keyed on?  kinda defeats the purpose... If i recall the clock should always even with no key.

Does anyone know how the tach was wired for a 78? as opposed to a 79 newer style 6k. I dont have any schems for it.. It seems as if that 12v should be going to battery if the clock was to always keep time?

Any direction would be appreciated.
Den


aussieta

  • Active Forum Member
  • *
  • Posts: 563
i believe there are 2 separate harnesses
one for tach and one for clock
1978 Y84 W72 WS6
A Camaro looks like it could kick your ass.
A Trans Am looks like it's coming over to do it

Den455

  • Forum Member
  • *
  • Posts: 5
There are only 2 connections on the Tach... along with a ground... No separate harness for clock.

jonathonar89

  • Oracle Forum Member
  • *
  • Posts: 1891
Yes, the clock always runs in normal conditions.

Den455

  • Forum Member
  • *
  • Posts: 5

Again... its not a factory connection.. Im looking at a 12V keyed ignition tap for the 12V.

Does anyone know what the pink and white go from the original factory connections?

thanks


aussieta

  • Active Forum Member
  • *
  • Posts: 563
1978 Y84 W72 WS6
A Camaro looks like it could kick your ass.
A Trans Am looks like it's coming over to do it

firebirdparts

  • Jedi Council
  • Oracle Forum Member
  • *
  • Posts: 18334
The text on our website was supposed to explain it, but in 1980, the tach wiring was no longer separate.  They integrated it.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

b_hill_86

  • Active Forum Member
  • *
  • Posts: 208
If you’re talking pink/white on the plug that goes into the back of the cluster I think it is the seatbelt warning wire.
-Brian-

1977 Trans Am 400 4 speed

b_hill_86

  • Active Forum Member
  • *
  • Posts: 208
And the clock is powered separately from the tach through the printed circuit on my 77 so since your 8k tach is earlier it is probably the same? I dunno about the later tach assembly’s with the quartz clock.
-Brian-

1977 Trans Am 400 4 speed

Den455

  • Forum Member
  • *
  • Posts: 5
Hi Brian

Thanks for the confirmation..

In case anyone needs to know.. i got the schematics and compared the years and yes the clock runs off the battery.

Regardless of year, 74-80, if its got the gauge package you can interchange the pcbs so you can use the 8k tach.. pcbs were changed just due to shape of back of the tachs... The pcbs function exactly electrically.

The tach harness has 12v out which wires into the IGN tap on the fuse panel and the other pin goes to the distributor or msd for tach signal.

Cheers!

firebirdparts

  • Jedi Council
  • Oracle Forum Member
  • *
  • Posts: 18334
Re: 8K tachometer in 1979 Trans Am.. will clock run with keyed ignition off?
« Reply #10 on: November 15, 2018, 12:08:31 PM »
You're right of course,  The clock is not powered by the tach harness.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Re: 8K tachometer in 1979 Trans Am.. will clock run with keyed ignition off?
« Reply #10 on: November 15, 2018, 12:08:31 PM »
You can help support TAC!