C2: 64-65 T.I. Coil Wiring

[Michael H.]

Since I am somewhat electronically challenged, I have what may be a stupid question about the primary wiring at the coil of a 64-65 with T.I. ignition. The 64-65 system is supposed to have the 20 ga black wire on the positive terminal of the coil and the 12 ga white resistance wire on the negative terminal. This changed in 66 with the 12 ga white resistance wire on the positive terminal and the 20 ga black non resistance wire on the negative terminal. The ultimate destination of these wires from each system was the same, just the wire changed. What's the deal?

[William C.]

Re: C2: 64-65 T.I. Coil Wiring

Michael, if you look carefully, I beleive there was a change in the wiring circuitry, I forget if it was 64/65 or 65/66, but I think there was an old "Restorer" article on it and possibly a service bulletin.

[Michael H.]

Re: C2: 64-65 T.I. Coil Wiring

Thanks Bill. I went to the T.I. Specialties site this AM and his wiring diagrams for 64-65 do show the black 20 ga wire on the positive terminal of the coil, unlike the 66-71 which reversed the order and has the 12 ga white resistor wire on the positive. Both diagrams show the positive terminal wire going to the amplifier.

[Clem Z.]

Re: C2: 64-65 T.I. Coil Wiring

the coil wiring polarity was changed to prevent the blowing of the amp if the coil input wiring was shorted to ground.

[Michael H.]

Re: C2: 64-65 T.I. Coil Wiring

Clem,

I don't think the polarity was changed, just the physical makeup of the wires. Both 1st and second design systems route the wires to the exact same place. The positive goes to the amp on both systems but it was black 20 ga in 64-65, then white 12 ga resistor wire in 66-71. It's confusing because the wires were reversed but only the wire, not the routing. Check out the dagram on the T.I. Specialties web page. www.tispecialty.com. Click on "T.I. Info" for the diagrams.

[Clem Z.]

Re: C2: 64-65 T.I. Coil Wiring

i may have used the wrong wording but the change was made for the the reason i posted to prevent the amp from blowing if a short accured according to a GM bulletin i had back then.

[Michael H.]

Re: C2: 64-65 T.I. Coil Wiring

Thanks Clem, that's what I was looking for. Just always wondered why the change. I know this has been a very confusing issue for many people for many years.

Looks like engineering wanted the resisted value to be on the neg side instead of the pos side.

I do know that if you try to use this 64-65 wiring diagram with a later service replacement harness, the car won't run.

[Wayne M.]

Chev Service News -- Nov '65

Here's probably what you were refering to; Issue shows both early configuration (white to coil neg) and the later (white to coil +ve).

"The following wiring diagrams for breakerless ignition systems superseded all other published diagrams for Chevrolet, Chevelle, Chevy II and Corvette. The "12 white" is a calibrated resistance wire located on the negative side of the ignition coil on 1965 vehicles. However, in 1966, this resistance is placed on the positive side of the coil for added protection of the ignition pulse amplifier in case of accidentally grounding the ignition coil wire. At the present time, the above does not apply to trucks."

This was the 2nd mod done to the breakerless system. Sometime in (early ?) 1965, a resistor (R6) was added to the circuit board of the amplifier, "to protect transistor TR-3 (the trigger transistor) from excessive current in case the pickup coil circuit is grounded". [from Delco service bulletin 1D-155, 7-1-65]

Of course, we all know the real reason was so that 40 years hence, resotration and judging would have something else to chew on.

[Clem Z.]

Re: C2: 64-65 T.I. Coil Wiring

i repaired these amps starting back in the 60s and still have my tester BUT ran out of replcement parts years ago. we just started using HEI modules after 74 to repair the systems.