Electrical Issue: Help/Advice Needed

[falude]

Hi All –

I’m having some electrical issues that I’d love some opinions on. This winter I had the instrument cluster out and reinstalled it with:

- Rebuilt Corsa tach (Vairtrix kit)
- New ignition switch
- Revolution Electronics fuel pump controller

I also had the powerpack out for a reseal/new clutch/bushings/etc. I just now got everything back together and am having some electrical issues:

- I did not have spark (either with my XR 700 ignition or a points plate) until after some troubleshooting I found that I had
spark (with points installed) when I disconnected the tach signal wire from the coil (negative coil terminal)

- When I got the car to fire up, I went to shut it down at the engine by pulling the negative battery cable, but it did not
quit running

- Later with the car not running but the ignition on, I had a wrench in my hand that sparked when it made contact with
the dash.

Disconnecting the fuel pump controller made no difference. I have the engine shroud grounds all connected and the battery grounded. It cranks good and all the lights work. What the heck do I have going on?

Thank you,
Matt

[66vairguy]

Matt -- The only thing I can think of is the alternator is grounded to the engine and if it is running it will supply power to items and they are grounded to the body and the body is grounded to the battery ground cable and via the engien tin radio ground straps. You basically just removed the battery, but the alternator stayed in the circuit and as long as the engine runs it supplies electrical power. BTW running an alternator without a battery connected is not recommended as the battery acts like a filter to "smooth" the alternator electrical output. It won't hurt the coil, but can damage the radio (if on) and electronic items - XR700, tachometer, etc. I AM NOT SAYING IT DID, but it could have! Today many items are engineered to deal with voltage transients.

So never disconnect battery cables UNTIL THE ENGINE IS STOPPED!

With the ignition switch on, the fuel gauge (and Corsa tachometer and temperature gauge) are powered up and the gauges ground to a strap the runs down the plastic housing and grounds to the dash frame via one little screw that holds the gauge housing in. THIS IS A NOTORIOUSLY PROBLEMATIC GROUND PATH. I install a 12 gauge ground wire from the instrument cluster ground strap to a good body metal connection!

The new Vartrix tachometer shorting the coil terminal to ground ( I assume) means the tachometer is shorted. It rarely happens with the factory tachometer, but is possible. More likely the wiring is not connected to the proper corresponding tachometer terminals.

Keep in mind I'm troubleshooting via a keyboard and could be wrong! Good luck.

[cnicol]

I agree with '66vairguy's assessments

Tachometer is shorting coil (-) to ground and killing spark

"Hot" dash is an ungrounded dash. You can fix the factory ground (strap held in contact with the dash frame by a small screw to the left of the steering column) or add a ground wire as '66 suggested.

Pulling the battery cable will not stop the engine. Power from the alternator is feeding the main battery circuit which goes up to the key and if the key is ON, power goes to the coil and the engine keeps running. Note that with the battery out of the circuit, the vehicle is subjected to potentially damaging electrical spikes from the alternator, ignition, and other items. These spikes can and will "take out" electronic equipment in the vehicle (radio/tach/alternator/electronic ignition, etc). Don't remove a battery cable while the engine is running.

[falude]

Thank you both for your help/diagnostics. I'll add a dash ground and check the connections at the tach.

Also, I'll no longer try to shut the engine down by disconnecting the battery while running.

I'll report back tomorrow once I dig into the wiring.

[bbodie52]

The Corsa and Monza instrument panels can develop problems with the electric instruments. The panels are plastic, so a metal conductive grounding strap links the electric gauges together and then ties them to chassis ground at a single point. If the single screw that attaches that grounding strap to the metal dashboard becomes loose or corroded, the electrical ground to the instrument panel components may be lost and this can disrupt the operation of the electric gauges and illumination lights.









What the Corsa ground strap spider looks like...



CORVAIR COMBINED WIRING SCHEMATIC DIAGRAMS
viewtopic.php?t=12968

[falude]

Thanks, Brad for the helpful diagrams.

Here are my findings from messing with the car tonight:

• - I had indeed forgot the ground screw at the dash - so that mystery is solved.
  
  - I believe the tachometer is shorted out. It smoked the 12 V power wire to it when I turned the ignition on tonight...I quickly disconnected power to the tach after that.
  
  - I am still having the issue where i have no spark when the tach signal wire is attached to the negative terminal of the coil, and I got a nasty shock reaching in to disconnect the signal wire from the coil tonight. The tachometer signal wire is hooked up to the revolution fuel pump controller at the moment but that is it. What do you think could be causing that?
  
  - I am wondering if my fuel pump controller is fried - it won't stop priming with keyed-on power. I wired the included diode into the fuel pump power circuit tonight and it didn't seem to help

That's where I'm at for the moment. This car worked better with the broken mechanical tach, points, and mechanical fuel pump (although i was on my third one in two years).

Any additional thoughts or insights are greatly appreciated. Thank you!

[63Spyderd]

When assembling the tach into the housing, it is important that the two red shoulder washers are centered in the housing holes. If not, or if they are missing, either the tach - or the +12V threaded posts can contact the housing and short either to ground. If the TACH- threaded post is shorted, the engine will not run. If the +12V post is shorted, it would likely blow a fuse.

There is no failure mode of an original tach or the Vairtrix rebuild kit circuit board assembly that can cause a short to ground at the TACH - terminal. This can only result from a mechanical fault between the posts and the housing.

It is recommended that you examine the assembly of the tach into the housing and ensure the shoulder washers are centered in the housing.

[Frank DuVal]

There is pulsating DC at the negative terminal of the coil. And also induced spikes from the opening of the points, which let the magnetic field collapse and make the high voltage spark, but also makes a pretty high (2-3 hundred spike) at the negative coil terminal, so don't fool with it while running.....

Just leave the tach wire disconnected until everything else works.

[66vairguy]

Thanks, Brad for the helpful diagrams.

Here are my findings from messing with the car tonight:

• - I had indeed forgot the ground screw at the dash - so that mystery is solved.
  
  - I believe the tachometer is shorted out. It smoked the 12 V power wire to it when I turned the ignition on tonight...I quickly disconnected power to the tach after that.
  
  - I am still having the issue where i have no spark when the tach signal wire is attached to the negative terminal of the coil, and I got a nasty shock reaching in to disconnect the signal wire from the coil tonight. The tachometer signal wire is hooked up to the revolution fuel pump controller at the moment but that is it. What do you think could be causing that?
  
  - I am wondering if my fuel pump controller is fried - it won't stop priming with keyed-on power. I wired the included diode into the fuel pump power circuit tonight and it didn't seem to help

That's where I'm at for the moment. This car worked better with the broken mechanical tach, points, and mechanical fuel pump (although i was on my third one in two years).

Any additional thoughts or insights are greatly appreciated. Thank you!

With no instruments ground I can't say if the Vairtrix tachometer was damaged A good design would allow for reverse polarity or an open ground (folks do make mistakes installing electronics). The old stock unit would not be damaged by no ground with power applied. I suspect 63 Spyder is correct about the insulators. I have seen this. I always check this area with a meter to case when I did tachometer repairs.

If you got a shock from the coil when removing the signal wire from the coil "-" terminal that suggests the coil "+" terminal was powered up at the time. Hmmmm.

After the negative battery cable disconnect issue, some of us stated it could damage the other electronic devices. Either the fuel pump controller was damaged, or it is not wired up correctly.

No offense --- but you may need the help of an experienced automotive electrical/Corvair person. Also I always proceed with "changes" by doing ONLY ONE THING AT A TIME AND VERIFYING BEFORE PROCEEDING TO THE NEXT CHANGE. One rule of troubleshooting is "WHAT DID YOU DO LAST BEFORE THE PROBLEM". When you change a number of things at once, that really complicates troubleshooting. Good Luck.

[flamingchariots]

- I am wondering if my fuel pump controller is fried - it won't stop priming with keyed-on power. I wired the included diode into the fuel pump power circuit tonight and it didn't seem to help[/list]

Was the diode installed in the correct direction (polarity)?



https://www.electroniclinic.com/wp-cont ... onents.png

[66vairguy]

- I am wondering if my fuel pump controller is fried - it won't stop priming with keyed-on power. I wired the included diode into the fuel pump power circuit tonight and it didn't seem to help[/list]

Was the diode installed in the correct direction (polarity)?



https://www.electroniclinic.com/wp-cont ... onents.png

Flamingchariots - I looked up the Revolutions Controller instructions. The diode IS NOT USED ON THE POWER SUPPLY INPUT. It is used across the controller output to power the fuel pump. The diode a is a "reverse EMF" diode. A common use across motor or solenoid to cancel power spikes when a motor or solenoid coil magnetic field collapses when power is interrupted. Same concept that makes an ignition coil put out a voltage surge when points open. The diode goes in reverse polarity (diode ban negative side to pump positive input to ONLY conduct reverse polarity at the fuel pump input and ground to shunt surges to ground instead of them going back up power supply to electronic device!!! See instructions for diode use.

[cnicol]

If you do conclude your Revolution fuel pump controller is fried and if it's out of warranty, you might consider using one of my fuel pump controllers instead. My design is much easier to install, costs less, and protects against low oil pressure. Also, my design does not require connection to the tachometer or coil (-) circuit.

[Frank DuVal]

Very interesting Craig! I like simple installations.

[63Spyderd]

The Vairtrix Tachometer Rebuild Kits are protected from reverse polarity and overvoltage however there is limited protection for a phenomenon referred to as "load dump". This can occur while the battery is disconnected while the generator or alternator is charging.

To further protect the tach during the condition of a load dump, a TVS diode is being provided by Clarks with each kit. The diode is installed between the +12V and Ground terminals on the back of the tach.

An addendum to the installation instructions is shown below.

If you were an early adapter of the tach kit and did not receive a TVS, it is recommended that you contact Clarks and have them ship you one.

As a reminder, please ensure your tach threaded studs are properly insulated from the housing with the red plastic shoulder washers. Also, ensure you have the proper size fuses in your vehicle and under no circumstances, should you disconnect the battery while the engine is running.

[66vairguy]

Thanks 63SPYDERD - Note sometimes a TVS (transient spike diode) can got to a short after operation. Good to check it.

[66vairguy]

63 Spyderd --- Do you know if the Vairtrix tachometer will fail if the GROUND is open and a voltage is applied to the input from the ignition coil? Reverse polarity circuits might not protect the chip if it is connected to power AND a tach signal WITHOUT a ground. Designing circuits for a car is complicated!!