Recommend + and- for tach - Team Camaro Tech
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post #1 of 9 (permalink) Old Dec 26th, 14, 05:59 PM Thread Starter
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Ken
 
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Recommend + and- for tach

Got a new tach and the instructions suggest running the pos and neg straight to the battery (but of course wires aren't long enough) and I don't want to do it that way if I don't need to.

Can anyone suggest a good alternative? I can probably find a really good ground so thats not a huge deal but the positive I'd like to use something close to the coil just so I have less wires running everywhere.
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post #2 of 9 (permalink) Old Dec 26th, 14, 07:02 PM
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Re: Recommend + and- for tach

What brand and model tach ?. Is there a link to the wiring diagram ?

On most basic tach installs, I would make the connections for power and illumination to the fuse block. I would also find out if the manufacturer recommends any kind of inline fusing on either or both of the power wire and illumination wire.
In the middle of the factory fuse block, there are 1/4" male terminals that allow accessories like a tach, aftermarket radio, aftermarket gauges, and such to get different types of power for them such as a constant 12 volts, an accessory 12 volts, an ignition 12 volts, and an illumination 12 volts that comes on when the parking lights are on and is also dimmable. I would power the tach off of the accessory or ignition (marked ACC or IGN on the fuse block) 12 volt terminal in the fuse block, connect up the tach's illumination wire to the LPS terminal on the fuse block, then ground the tach to either an existing firewall bolt or find a good metal spot on the firewall to connect to solidly. For the signal wire that would connect to either the coils negative terminal on a normal points ignition or to the HEI's TACH, use an existing hole in the firewall that has a rubber grommet in it.
If the manufacturer suggests something like a 10A fuse, put this fuse close to the fuse block so that if the wire ever gets shorted past it, the fuse will blow. Also crimp on a ground ring terminal to the tach's ground wire and don't just wrap it around or under a bolt.

Jim

1974 Spirit Of America Nova (being restored), 1973 Nova Custom, 1968 Chevy II (Garage Find 2012)

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post #3 of 9 (permalink) Old Dec 26th, 14, 07:20 PM Thread Starter
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Ken
 
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Re: Recommend + and- for tach

Quote:
Originally Posted by SOA-Nova View Post
What brand and model tach ?. Is there a link to the wiring diagram ?

On most basic tach installs, I would make the connections for power and illumination to the fuse block. I would also find out if the manufacturer recommends any kind of inline fusing on either or both of the power wire and illumination wire.
In the middle of the factory fuse block, there are 1/4" male terminals that allow accessories like a tach, aftermarket radio, aftermarket gauges, and such to get different types of power for them such as a constant 12 volts, an accessory 12 volts, an ignition 12 volts, and an illumination 12 volts that comes on when the parking lights are on and is also dimmable. I would power the tach off of the accessory or ignition (marked ACC or IGN on the fuse block) 12 volt terminal in the fuse block, connect up the tach's illumination wire to the LPS terminal on the fuse block, then ground the tach to either an existing firewall bolt or find a good metal spot on the firewall to connect to solidly. For the signal wire that would connect to either the coils negative terminal on a normal points ignition or to the HEI's TACH, use an existing hole in the firewall that has a rubber grommet in it.
If the manufacturer suggests something like a 10A fuse, put this fuse close to the fuse block so that if the wire ever gets shorted past it, the fuse will blow. Also crimp on a ground ring terminal to the tach's ground wire and don't just wrap it around or under a bolt.

Jim

Thanks, this is exactly the info I wanted/needed!
Its sort of a cheapy tach. A mini one I got for christmas which just mounts on the steering column until I decide which direction I'm going (thinking the dakota digital gauges). But I wanted something in the meantime.

I did test it under the hood and started the car, works fine, but had it connected to the battery and negative on coil. The instructions say nothing about inline fusing but I think I will do that anyway. I'll check the instructions again and make sure.
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post #4 of 9 (permalink) Old Dec 26th, 14, 07:28 PM Thread Starter
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Ken
 
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Re: Recommend + and- for tach

Actually i was wrong. It says connect the red to the fuse block with 'ignition on terminal' and negative should be the battery since under the dash can cause interference.
And lighting is on the fuse block as well.

http://www.sunpro.com/publish/2007/0...lish_16474.pdf

So i believe your instruction was correct and I will go with that. I just didn't realize the stock fuse block had these options.

thanks again
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post #5 of 9 (permalink) Old Dec 26th, 14, 07:38 PM
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Re: Recommend + and- for tach

Yeah and any point on the dash frame will get you a good ground.


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post #6 of 9 (permalink) Old Dec 26th, 14, 07:52 PM
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Re: Recommend + and- for tach

The fuse block has output options but they are limited as to how much power they can supply. Adding a small thing like a tach that probably draws 3-5 amps should not present any kind of problems.
To get an idea of what size fuse to possibly add would be to look at the wire size used on the tach. You can then do a search online and find out what a particular gauge wire can handle. I'm going to guess the tach wire is maybe an 18 gauge and if it was I would probably install at maximum a 10A fuse. Keep in mind the terminals on the fuse block for adding accessories are fused by neighboring fuses already in place. When I'm adding circuits in cars with added fuse holders I try and use the same type of fuse so there is more standardization. The new cars today use all different physically sized fuses and it's hard to keep a spare for all of them should any of them blow. The older cars are easier.

Jim

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post #7 of 9 (permalink) Old Dec 27th, 14, 10:38 AM Thread Starter
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Re: Recommend + and- for tach

I have it installed and its working. One question though. I used the extra terminals (ignition one) and the one labeled LPA (I think) for the illumination. But since the terminal for ignition is in the center how do I know which fuse it is associated with?
There is a 10amp and 20amp on either side of it.
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post #8 of 9 (permalink) Old Dec 27th, 14, 11:37 AM
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Re: Recommend + and- for tach

On the extra terminals on the fuse block you just need to think about how it could be and the right way will be evident.
On my 68 Nova there is a top center terminal labeled BAT for battery. This terminal is connected onto the backside of the fuse clip on the fuse to the left. How do I know that you might ask. The fuse to the left of it is labeled CIG LTR and CTSY. The CIG LTR stands for cigarette lighter and the CTSY stands for courtesy lights and these I know work all of the time so this would have to be a constant 12 volts. The fuse to the right of the BAT terminal is labeled HEATER A/C and the heater and A/C only work while the key is NOT in the off position.
Now if I look to the next center terminal below the one marked BAT it is labeled ACC and the fuse on the left is marked TAIL and the fuse on the right is labeled RADIO. On this one I think either fuse could be connected to the terminal marked ACC but since I'm not 100% sure I would be turning the ignition switch to accessory, verifying I had 12 volts on the center ACC terminal and then popping out the left and then the right fuse next to it to see when the ACC terminal went dead and then this would be the fuse connected to it.
On the IGN terminal, the fuse to the left is labeled STOP and HAZ and that is a constant 12 volt but the DIR SIG fuse to the right only works wen the ignition is in the run position so that IGN terminal is connected to that side (the right fuse).
On the LPS terminal the fuse to the left is labeled INST LPS and this small fuse protects the LPS terminal.

If you want to verify things, use a test light and see when a particular terminal in the fuse block goes dead when a neighboring fuse is removed. You will though on some circuits have to have the ignition switch in a particular spot like off, accessory, and run but to test the LPS circuit you need to pull on the headlight switch to the parking light position.

Jim

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post #9 of 9 (permalink) Old Dec 27th, 14, 02:50 PM Thread Starter
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Re: Recommend + and- for tach

Thanks Jim
That explains it. You can't go wrong with logic! I'll check into it just to be sure but its all working great as of now. The hardest part is organizing and hiding the wires so it looks nice.
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