Author Topic: Repro tach burned out  (Read 4007 times)

lemarin

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Repro tach burned out
« on: September 11, 2016, 12:34:43 AM »
During my engine restoration last winter, I add to my 69 RS the optional instrument pack, sold by heartbeat Camaro.

I also installed a Pertronix from eBay.

I drove the car for about 1 month then smoke came out from the dash and the tach was gone. I installed another repro tach, and it last for about 2 hours then burned out as well. What's the problem ? The tach is connected to the negative pole of the Pertronix, is there an incompatibility?

Any idea is appreciated ? Thanks to all!
 !
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L78 steve

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Re: Repro tach burned out
« Reply #1 on: September 12, 2016, 02:24:52 PM »
I have a Pertronix Ign. conversion on my 67 with Factory tach with no issues.
Are you wired to the Neg. post on the coil?
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lemarin

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Re: Repro tach burned out
« Reply #2 on: September 12, 2016, 02:47:15 PM »
Good morning Steve and thanks for the reply. The tach is (was) connected on the negative on the Pertronic coil. I unhooked it this morning and made some continuity test. It seems that both positive and negative on the Pertronic coil have continuity, is it normal ? I touch the car's frame with one end, touch the negative and it bips, touch the positive and it bips as well. When I touch both, positive and negative on the coil there is conductivity. I might have a wire grounded/dammaged somewhere.....
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Kelley W King

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Re: Repro tach burned out
« Reply #3 on: September 12, 2016, 06:50:20 PM »
Continuity testers have a purpose but serious tests call for an ohm meter. Things that use electricity mostly do this by a controlled short circuit between positive and negative. For instance if you put your beep tester on a light bulb it will show continuity because it reads through the filament which is the controlled short, ( the heat of the resistance is the glow of the lamp). If you use an ohm meter it will not show 100% continuity. Between the pos and neg of a coil you will see continuity through the windings but not 100%. Most test proceedures will give specified ohm readings. Harbor Freight sometimes have coupons for free meters but their accuracy is ???.
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69Z28-RS

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Re: Repro tach burned out
« Reply #4 on: September 12, 2016, 07:09:00 PM »
Kelley is right..  please don't make decisions about electronics or electric circuits based on a 'continuity tester'.  Here is the very inexpensive meter that Harbor Freight sometimes gives away  'with a purchase'...

http://www.harborfreight.com/7-function-digital-multimeter-90899.html

It's not a $200 Fluke meter, but it's cost is only $5.99 (or Free) and it's much better for testing than a 'light'.  I have a couple of these that I keep handy in my garage for 'quick checks', leaving my good Fluke meter in my electronic tool bag for more serious tasks..  :)
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jdv69z

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Re: Repro tach burned out
« Reply #5 on: September 12, 2016, 07:10:14 PM »
Yes, if you think about it, if there was 100% continuity between the + and - sides of the coil, that would be a dead short.
Jimmy V.

lemarin

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Re: Repro tach burned out
« Reply #6 on: September 12, 2016, 07:25:43 PM »
I understand that it's normal to have a certain amount of continuity between both poles. I took off both connected wires, fro both, the negative and the positive pole. On the positive pole, there was a red wire (from the positive pole, from battery maybe, or ignition) and another unknown wire (not sure for what purpose). Anyway, when I check once again the conductivity between those two wires originally hooked on the positive of the coil, and a bolt on the frame, there is conductivity.....What is suppose to be the second wire on the positive ?
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Kelley W King

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Re: Repro tach burned out
« Reply #7 on: September 12, 2016, 08:09:23 PM »
You really need an ohm meter. Almost everything with a connection to ground is somehow connected to positive through a device that could show continuity. If through an off switch maybe not, but if you have a clock? no switch. Something like this can backfeed through the entire system. But back to you real question. I would isolate both ends of the tach wires and check ohms to ground. I had an intermittent problem ( that burned the tach up) which ended with a wire rubbing metal going through the firewall but only if you hit a bump or something. Maybe when you did the Petro you pulled one too hard? Years ago on an all night shut down while installing a genset we found continuity to ground on a 1600 amp 480 volt panel. (not good), turned out to be the voltage meter on the main switch. Good luck with your Gremlins, you might need Ghost Busters.
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KurtS

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Re: Repro tach burned out
« Reply #8 on: September 13, 2016, 12:15:55 AM »
This is a good multimeter. https://www.amazon.com/INNOVA-3320-Auto-Ranging-Digital-Multimeter/dp/B000EVYGZA/
I got it for $18, it's now $28. :(
There are others, but I highly recommend getting an auto-ranging model.
Kurt S
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lemarin

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Re: Repro tach burned out
« Reply #9 on: September 13, 2016, 12:37:53 AM »
I do have an multimeter at home, just taught the continuity was the right way to check. Per example, if I check resistance using both end of a 3-4 feet wire, what should be the resistance ? Then if the same wire is damaged, what can of resistance should I get ?
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JoeC

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Re: Repro tach burned out
« Reply #10 on: September 13, 2016, 01:19:53 AM »

The points run on a resistance wire with about 9.7 volts
on cranking its 12v but runs on 9.7v
many aftermarket ignition run on 12v and don't use the factory resistance wire but  factory tach still needs the lower volts

here is a link


http://www.tachman.com/tshoot.htm

69Z28-RS

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Re: Repro tach burned out
« Reply #11 on: September 13, 2016, 01:20:42 AM »
I do have an multimeter at home, just taught the continuity was the right way to check. Per example, if I check resistance using both end of a 3-4 feet wire, what should be the resistance ? Then if the same wire is damaged, what can of resistance should I get ?

If you are checking the two ends of a single wire (to see if it's cut or good?), then a continuity checker is generally fine.. because the wire is generally 'good' or is cut/broken/damaged.  Note:  if that wire is shorted to ground somewhere in the middle, or shorted to another wire, you'll still get good continuity (near zero resistance), so you should also to check each end of the wire to 'Gnd' and to 'Hot'.

A 3-4 ft length of common automotive wire should have a very low resistance if good (near zero), but shoudl read *open* if it's cut (assuming both ends are separated from any other circuits)..
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jdv69z

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Re: Repro tach burned out
« Reply #12 on: September 13, 2016, 03:12:01 PM »
I do have an multimeter at home, just taught the continuity was the right way to check. Per example, if I check resistance using both end of a 3-4 feet wire, what should be the resistance ? Then if the same wire is damaged, what can of resistance should I get ?

If you test resistance on a 3' piece of wire, it should measure 0, that is, you have a connection or continuity, no measurable resistance, although theoretically there would be some very small amount. If the wire were to somehow become broken, the meter would read infinite resistance, ie , no continuity, no connection.

Just understanding this and being able to use it to test wiring can help discover a lot of problems with wiring.
Jimmy V.

lemarin

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Re: Repro tach burned out
« Reply #13 on: September 13, 2016, 07:40:39 PM »
Ok thanks for the course about resistance, it's very interesting !

Now can you guys help me to find out how it is suppose to be connected...originally, so I can test all 3 wires, at their both ends ? From behind the tach, "coil" is connected to the negative of the Pertronix. "ground" has to be grounded somewhere near by the back of the tach, on the body ? And what about the third pole, the "12V" connector ? Where should it be connected ? Maybe I should directly route 3 independent brand new wires, and see how it goes......But I still have to order a new tach before to make any test !
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lemarin

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Re: Repro tach burned out
« Reply #14 on: September 16, 2016, 04:52:33 PM »
One more sign of a damaged wire. Right now the tach is still connected, except the wire going to the Pertronix, is unhooked. This one is normally hooked on the negative of the Pertronix. When I started the car this morning, the tach needle rises up, to maybe 1500 RPM for 10-15 second, and then it came back down.
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