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280z Speedometer


Guest Anonymous

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Guest Anonymous

Hi there,

I have a 1977 280z speedometer. There is a small box mounted to the back of the speedometer housing, A red wire comes out from the speedo head

and connects to this small "box", there are also a couple of green wires coming out of this box that and go into the wiring harness.

Can you tell me what the purpose of this small "box" is??

Will it affect the speedometer if it is removed??

Someone told me that it is a 12V Voltage stabilizer???

I am going to use this speedometer in a hot rod that I am building. I need to hook this speedo up to a Turbo 350 Auto trans.

Please help if you can OR point me in the right direction for some help.

 

Thanks

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This is interesting because I'm not sure how many people want to touch this kind of thing icon_biggrin.gif

 

The picture I have is black and white and does not show the 'box' you speak of. The instructions are written for making the 280 speedo guts work in the 240 housing with a SBC Chevy & HEI. I don't know if this is what you are after, but if so, here is the scoopy:

 

1) Remove plastic housing from case.

2) remove nuts that secure wires to back of tach, and the nuts beneath the wires.

3)Remove the Phillips head screw from back of tach.

4)Push 'guts' of tach through front of tach housing.

5)Remove guts from 280Z tach same way.

6)Install guts from 280Z into 240Z case--make sure that the ground wire and power wires are reversed (they are the ones held by nuts).

7)The sensing wire on the 240Z comes from the ballast resistor and goes to the positive side of the ignition coil (it is the white wire that does a loop on the back of the tach). Cut the white wire and attach a 15K ohm, 1/2 watt resistor to the side with the black band around it. Connect this to the sensing terminal on the 280Z tach. The white wire with red band should not be used, so just tape it up.

8)In wiring the HEI disty, connect the black-white wire in the engine compartment to the BAT terminal on the disty. Connect the other black-white wire to the TACH terminal on the disty (on neg side of coil). Attach green-white wire to fuel pump wiring.

 

HTH,

Davy

 

8)

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Guest Anonymous

THANKS for the reply. BUT----------

This little "box" is on the back of the speedometer,it is about 1 1/2" X 1" X 3/4".

It sits right next to where the speedo cable

attaches to the back of the speedo head. It is held on to the speedo housing with one screw that

has a black ground wire also. The "BOX" itself

has ONE red wire coming out and connecting to

the red wire that comes out of the speedo head.

(through the speedometer housing)

There is also a green wire and a green w/pink

stripe wire that comes out of it and hooks into the rest of the wiring harness for the speedometer lighting.

The "BOX" has the part #68600-AJ3900 stamped on the back of it.

Since my first post someone has told me that it is a 12V voltage "regulator" to keep no more than

12 volts going to the gauges. It protects the

instruments from voltage spikes.

Can anyone confirm this???????

By the way I am talking about the back of the speedometer, not the Tach.

Thanks

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Guest Anonymous

I cant believe that none of you Z car guys know what this little "BOX" on the back of the speedo is!!!

Do any of you have a 1977 280z wiring manual??

Does it show this "BOX"??

If it does, What is it??

Someone, anyone?? Please??

 

Thanks!

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Guest Anonymous

I believe(?) that after consulting a 78 shop manual the red and green wires are interconnected thruout the dash wiring harness as illumination sources going to a rheostat for dimming or brightening all the lights in the dash. The manual does not indicate a black box. There are two illumination lamps,one high beam warning lamp ,trip counter reset cable and brake warning lamp with all wires(including ground wire) leading into an 8 pin male connector from the speedometer.The box may be some kind of electrical stabilizer/booster or other nonesense for all the illumination lamps and would only interfere with total dash and indicator illumination if removed. Automatic transmission and cosole were illuinated too.??????????????

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