To those whom have messed with the 7 grand camaro tach... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Longhorn Man · 01-03-2004, 12:37 AM

I have one sitting here that I need to test. There are 2 wires on the back of it, a white and a black.
Anyone know which is which? I think I may have fried the one I had last time by hooking it up improperly...don't wanna screw this one up too.

*rage'nrat638* · 01-03-2004, 12:42 AM

my guess would be black - side of coil/ wht. ground

Longhorn Man · 01-03-2004, 01:25 AM

Problem is, one wire should be tach, one wire for 12 volts, and then grounds through the mounting....
So I still need info.

Solver · 01-03-2004, 01:39 AM

heres a picture of the back of mine
You can't see inpicture but the metal plate is labeled

Solver · 01-03-2004, 01:50 AM

Longhorn man your picture doesn't seem to show the circuit board on the back and I think all the diodes and resisters are needed for the tach to run
heres a pic with the circuit board attached
I have done about 5 of these Camaro Tach conversions so let me know if I can help you out with any questions

Longhorn Man · 01-03-2004, 01:53 AM

Hmmm...I left that backing plate in the camaro.

Longhorn Man · 01-03-2004, 01:55 AM

Well, the plate is 1000 miles south of here. Can you look and tell me which wire goes to which terminal?
I guess I'll find out if we need all that stuff on the back huh?

Solver · 01-03-2004, 02:12 AM

Longhorn man can you say road trip?
I tried to diassemble mine as far as yours but that back plate won't even budge.
I can tell you that my first picture shows your 3 same connections capped off with the plastic screw covers. There are no wires on mine as it feeds through the circuit board to the 2 connections you no longer have, that I have listed as coil and 12 volt. I tried tracing the cicuit board but it goes through way to many resistors and diodes you just can't follow. I hate to tell you this but I am pretty sure your missing to much to even try to make it work. I would even be afraid of frying your hei coil maybe?
Sorry
Solver

Longhorn Man · 01-03-2004, 02:34 AM

Hmmmm.
Something else that may be the differance here..mine came off a 74 or so...I remember the rear window did not curve down onto the side...it had the flat(ish) rear glass. I wonder if mine not haviong all the circuit board gizmo crap is becouse it is (probably) an older model than yours?
Oh well...Maybe I'll do the eni-mini-miny-moe trick tomorow.

Solver · 01-03-2004, 02:59 AM

not sure what year you have. Maybe 1973. I think my previous pictures were for 1978-1981 tach
I have included a pic of I think 1974-1977 tach.
the only difference between the 2 is that the older of these 2 has a flat smooth center and it is totally black where as the 1978 and newer orange part of the needle goes all the way through the center.
there are 2 rivets on the face of either of these(at 10 and 60) in the same location but not the same location as yours.

Alexis · 01-03-2004, 03:30 AM

Have you tryed hooking a meter to it. one way or another the meter can tell which wire is ground or positive.

GMC Jim · 01-03-2004, 07:41 AM

Using a good volt/ohmeter; suggest you check out the connections....In DC automotive circuitry; most always the black colored wiring was Battery negative/Ground. In other meter applications; a wire is used (black) for an auxillary ground for those installations that the meter case itself is not grounded thru it's mountimg ( such as plastic/fiberglass bezels, etc.). So, if your meter shows no resistance betweeen the meter case and the black wire; I would suspect the black wire is an auxillary ground, as I stated above...... Just my .02......Jim

Longhorn Man · 01-03-2004, 09:12 AM

Thanks for the help guys. We'll see what happens.

teeitup · 01-03-2004, 11:03 AM

Whats one of those worth out of curiousity? Thanks Randy

neonlarry · 01-03-2004, 01:15 PM

Well, I got mine for free, and a brand new one is about $75. If that helps. lol

neonlarry · 01-03-2004, 04:04 PM

Andy, that meter will not work as a Tach without the circuit board.
All you have is a voltmeter the circuit converts the ignition pulses to volts (the more pulses the more volts). Thats why there are only two leads, one to plus side of circuit one to minus. And my recollection is that the voltage rating of that meter is pretty low, meaning less than 12V. If you want I can look for a circuit board next time I hit the yards.

72superBB · 01-03-2004, 07:40 PM

Here is a copy of the back of my 79 camaro tach I received in the mail today. It has 3 screw terminals on the back. One says COIL and the other says 12V, but what is the 3rd one for?

And for the idiot in me, can you tell me exactly where on the truck the wires go to?

COIL goes where exactly?

12V goes to ignition power or the same power source as the dashlights?

thanks

Longhorn Man · 01-04-2004, 01:14 AM

super, on yours the 12 volt terminal would go to a terminal on your fuse box labeled ACC. This will turn on the power whenever your ignition is on. The one labeled coil, would go to the negitive side of the coil if you still have the points, or to the TACH spade terminal on an HEI set up...right beside the 12 volt wire that powers the distributor. Your third unlabeled terminal is posably for mounting on the original inst panel...but can certianly be used to ground the unit. If you look, you'll see it is not insulated from the backing plate like the other 2 posts are.

72superBB · 01-04-2004, 02:25 AM

THanks Longhorn.

Guess what I will be doing tomorrow? It is supposd to be pretty cold, but nothing I can't do indoors. I'll have to kick the wife's van out of the garage!

See ya

Ron

dmec · 01-05-2004, 05:27 AM

the what for terminal is for a ground

01-03-2004, 12:37 AM	#1
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	To those whom have messed with the 7 grand camaro tach... I have one sitting here that I need to test. There are 2 wires on the back of it, a white and a black. Anyone know which is which? I think I may have fried the one I had last time by hooking it up improperly...don't wanna screw this one up too. Attached Images

01-03-2004, 01:39 AM	#4
Solver Registered User Join Date: May 2000 Location: Storm Lake, Ia Posts: 1,449	heres a picture of the back of mine You can't see inpicture but the metal plate is labeled Attached Images __________________ 1972 Cheyenne Super 20 LWB-Blue 1972 Cheyenne Super 10 LWB-Black 1972 Cheyenne Super 10 LWB-Red 1972 Cheyenne Super 10 LWB-green 1972 GMC 4x4 LWB-White 1971 Cheyenne 10 LWB-Ochre 1971 Cheyenne 20 Longhorn-Copper 1971 Cheyenne 20 Longhorn-Black 1969 Custom 10 LWB-lt blue 1968 GMC 3/4 ton-green 1968 1/2 ton swb stepside-silver 1967 Chevrolet CST 10 LWB-green 1967 Chevrolet custom 20 LWB-Maroon

01-03-2004, 01:50 AM	#5
Solver Registered User Join Date: May 2000 Location: Storm Lake, Ia Posts: 1,449	Longhorn man your picture doesn't seem to show the circuit board on the back and I think all the diodes and resisters are needed for the tach to run heres a pic with the circuit board attached I have done about 5 of these Camaro Tach conversions so let me know if I can help you out with any questions Attached Images __________________ 1972 Cheyenne Super 20 LWB-Blue 1972 Cheyenne Super 10 LWB-Black 1972 Cheyenne Super 10 LWB-Red 1972 Cheyenne Super 10 LWB-green 1972 GMC 4x4 LWB-White 1971 Cheyenne 10 LWB-Ochre 1971 Cheyenne 20 Longhorn-Copper 1971 Cheyenne 20 Longhorn-Black 1969 Custom 10 LWB-lt blue 1968 GMC 3/4 ton-green 1968 1/2 ton swb stepside-silver 1967 Chevrolet CST 10 LWB-green 1967 Chevrolet custom 20 LWB-Maroon

01-03-2004, 01:53 AM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Hmmm...I left that backing plate in the camaro. Attached Images

01-03-2004, 02:12 AM	#8
Solver Registered User Join Date: May 2000 Location: Storm Lake, Ia Posts: 1,449	Longhorn man can you say road trip? I tried to diassemble mine as far as yours but that back plate won't even budge. I can tell you that my first picture shows your 3 same connections capped off with the plastic screw covers. There are no wires on mine as it feeds through the circuit board to the 2 connections you no longer have, that I have listed as coil and 12 volt. I tried tracing the cicuit board but it goes through way to many resistors and diodes you just can't follow. I hate to tell you this but I am pretty sure your missing to much to even try to make it work. I would even be afraid of frying your hei coil maybe? Sorry Solver __________________ 1972 Cheyenne Super 20 LWB-Blue 1972 Cheyenne Super 10 LWB-Black 1972 Cheyenne Super 10 LWB-Red 1972 Cheyenne Super 10 LWB-green 1972 GMC 4x4 LWB-White 1971 Cheyenne 10 LWB-Ochre 1971 Cheyenne 20 Longhorn-Copper 1971 Cheyenne 20 Longhorn-Black 1969 Custom 10 LWB-lt blue 1968 GMC 3/4 ton-green 1968 1/2 ton swb stepside-silver 1967 Chevrolet CST 10 LWB-green 1967 Chevrolet custom 20 LWB-Maroon

01-03-2004, 12:42 AM	#2
rage'nrat638 Account Suspended Join Date: Mar 2003 Location: THE FALL GUY CHICAGO IL Posts: 5,883	my guess would be black - side of coil/ wht. ground

01-03-2004, 01:25 AM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Problem is, one wire should be tach, one wire for 12 volts, and then grounds through the mounting.... So I still need info.

01-03-2004, 01:55 AM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Well, the plate is 1000 miles south of here. Can you look and tell me which wire goes to which terminal? I guess I'll find out if we need all that stuff on the back huh?

01-03-2004, 02:34 AM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Hmmmm. Something else that may be the differance here..mine came off a 74 or so...I remember the rear window did not curve down onto the side...it had the flat(ish) rear glass. I wonder if mine not haviong all the circuit board gizmo crap is becouse it is (probably) an older model than yours? Oh well...Maybe I'll do the eni-mini-miny-moe trick tomorow.

01-03-2004, 02:59 AM	#10
Solver Registered User Join Date: May 2000 Location: Storm Lake, Ia Posts: 1,449	not sure what year you have. Maybe 1973. I think my previous pictures were for 1978-1981 tach I have included a pic of I think 1974-1977 tach. the only difference between the 2 is that the older of these 2 has a flat smooth center and it is totally black where as the 1978 and newer orange part of the needle goes all the way through the center. there are 2 rivets on the face of either of these(at 10 and 60) in the same location but not the same location as yours. Attached Images __________________ 1972 Cheyenne Super 20 LWB-Blue 1972 Cheyenne Super 10 LWB-Black 1972 Cheyenne Super 10 LWB-Red 1972 Cheyenne Super 10 LWB-green 1972 GMC 4x4 LWB-White 1971 Cheyenne 10 LWB-Ochre 1971 Cheyenne 20 Longhorn-Copper 1971 Cheyenne 20 Longhorn-Black 1969 Custom 10 LWB-lt blue 1968 GMC 3/4 ton-green 1968 1/2 ton swb stepside-silver 1967 Chevrolet CST 10 LWB-green 1967 Chevrolet custom 20 LWB-Maroon

01-03-2004, 03:30 AM	#11
Alexis Member since 2000 Join Date: Dec 2000 Location: Mountain View Ca / Mexico Posts: 7,874	Have you tryed hooking a meter to it. one way or another the meter can tell which wire is ground or positive.

01-03-2004, 07:41 AM	#12
GMC Jim Senior Member Join Date: Dec 2002 Location: Portland, Oregon Posts: 901	Using a good volt/ohmeter; suggest you check out the connections....In DC automotive circuitry; most always the black colored wiring was Battery negative/Ground. In other meter applications; a wire is used (black) for an auxillary ground for those installations that the meter case itself is not grounded thru it's mountimg ( such as plastic/fiberglass bezels, etc.). So, if your meter shows no resistance betweeen the meter case and the black wire; I would suspect the black wire is an auxillary ground, as I stated above...... Just my .02......Jim __________________ '71 GMC;fleetside;PB/PS/AC/CC/402 Eng./Custom Paint/110,000act miles/3 fuel tanks(52gal).

01-03-2004, 09:12 AM	#13
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Thanks for the help guys. We'll see what happens.

01-03-2004, 11:03 AM	#14
teeitup Just like to part out trucks!! Join Date: Nov 2001 Location: Meriden, Ks-North of Topeka 10 miles Posts: 27,395	Whats one of those worth out of curiousity? Thanks Randy __________________ 67 Chev swb stepside 4x4 283 4 speed SOLD 72 blazer 4x4 4 speed Cheyenne 72 GMC swb 4x4 fleet 4 speed, original paint 1958 Cameo (one of 1405 built, it was my dads) 2020 chevy Apex 4x4 crew cab 1969 Z28 with the 302 1980 chevy swb 4x4 1964 chevell Malibu SS 1976 K20, sold new originally out of my dads chevy dealership Members that I've met, over 200 probably closer to 300 in the 12 years I've been on this site, everyone I met "It was a pleasure"

01-03-2004, 01:15 PM	#15
neonlarry Registered User Join Date: Feb 2002 Location: Vacaville, CA Posts: 2,745	Well, I got mine for free, and a brand new one is about $75. If that helps. lol __________________ 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI



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01-03-2004, 04:04 PM	#16
neonlarry Registered User Join Date: Feb 2002 Location: Vacaville, CA Posts: 2,745	Andy, that meter will not work as a Tach without the circuit board. All you have is a voltmeter the circuit converts the ignition pulses to volts (the more pulses the more volts). Thats why there are only two leads, one to plus side of circuit one to minus. And my recollection is that the voltage rating of that meter is pretty low, meaning less than 12V. If you want I can look for a circuit board next time I hit the yards. __________________ 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI

01-03-2004, 07:40 PM	#17
72superBB Registered User Join Date: Nov 2003 Location: Mandan, ND Posts: 422	Here is a copy of the back of my 79 camaro tach I received in the mail today. It has 3 screw terminals on the back. One says COIL and the other says 12V, but what is the 3rd one for? And for the idiot in me, can you tell me exactly where on the truck the wires go to? COIL goes where exactly? 12V goes to ignition power or the same power source as the dashlights? thanks Attached Images __________________ Life is full of choices and a Chevy is the best choice. 1990 Chevy SWB Last edited by 72superBB; 01-03-2004 at 07:50 PM.

01-04-2004, 01:14 AM	#18
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	super, on yours the 12 volt terminal would go to a terminal on your fuse box labeled ACC. This will turn on the power whenever your ignition is on. The one labeled coil, would go to the negitive side of the coil if you still have the points, or to the TACH spade terminal on an HEI set up...right beside the 12 volt wire that powers the distributor. Your third unlabeled terminal is posably for mounting on the original inst panel...but can certianly be used to ground the unit. If you look, you'll see it is not insulated from the backing plate like the other 2 posts are.

01-04-2004, 02:25 AM	#19
72superBB Registered User Join Date: Nov 2003 Location: Mandan, ND Posts: 422	THanks Longhorn. Guess what I will be doing tomorrow? It is supposd to be pretty cold, but nothing I can't do indoors. I'll have to kick the wife's van out of the garage! See ya Ron __________________ Life is full of choices and a Chevy is the best choice. 1990 Chevy SWB

01-05-2004, 05:27 AM	#20
dmec Senior Member Join Date: Jun 2000 Location: yucaipa ca Posts: 580	the what for terminal is for a ground

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