Electrical Problem... Options

[michaelmoo]

I first want to thank everyone who helped with my last electrical question. The car runs. Kinda. I had the wires for the coil and distributor unplugged and you guys came to the rescue. Now here is my new problem. The black/purple wire goes to the + side of the coil, the red from the Pertronx goes to the + side of the coil. The black from the Pertronx goes to the – side of the coil. Now I have one more black wire (tach) that SHOULD go to the – side of the coil. The car will turn over but not crank. I unplug the tach wire and it will fire right up. WHY? I want my tach to work. Porsche put it in the center for a reason!!

[ClayPerrine]

Check the wiring on the back of the tach. If someone plugged the tach lead into the ground point on the back of the tach, the car won't run. Or a simple anti-theft device is to add a toggle switch that grounds the tach lead on the back of the tach. Either may be the problem. Another remote possiblity is the tach is bad and grounding internally.

[michaelmoo]

thanks. I will check that this weekend.

[Dave_Darling]

The black/purple tach wire goes to the (-) terminal of the coil, not the (+) terminal. There's a black/red (or all black) wire that should go to the (+) side of the coil; it carries +12V there. Check the wire when the key is on for +12V. Hopefully you didn't get it backwards, the Pertronix doesn't like that. (It also doesn't like when you leave the key on for more than ~30 seconds without the engine on, nor does it seemingly like when the dog sneezes, or....)

--DD

[aircooledboy]

nor does it seemingly like when the dog sneezes, or....)

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[ClayPerrine]

Funny... 5+ years running a pertronix. Not a single problem with it. Right after getting the car back up and running (Betty's 914) I had a compufire in it. That lasted only about 6 months before it left us stranded on the side of the road.

I have a pertronix in 2 other cars too. Both of them (74 Corvette, 55 Chevy Bel-Air) have run fine since installation.

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[Spoke]

I had exactly the same problem with my car not firing. For the longest time I thought I had a vibrational miss. When I'd hit a pothole or bump, the engine would hickup. I thought it was the points so I put in a Pertronix and the car would not fire. So I removed the tach wire and it fired right up. With the car turned off, I started measuring the resistance of the tach wire to ground and found out that the wire from the distributor to the relay box would short to ground at times. Sometimes I'd move the wire and get an open circuit (to ground) which is what I expect. Then another bump of the wire and a short circuit to ground -> very bad. I cut the existing wire off about 2 inches from the connector to the relay box and ran a wire from there to the distributor. Problem solved.

Bottom line, measure resistance of the tach wire to ground starting at the distributor and you should see an open circuit or at least a high impedance. If a low impedance is measured, disconnect the engine wire bundle connector to the relay box. If the low impedance remains, its the wire across the engine like mine was. If not, the wire problem is between the relay box and the tach. Then disconnect the wire on the tach and measure the wire. If it is low impedance, its the wire. If the tach is low impedance, then its the tach. I'll bet its the wiring.

Spoke