Coil voltage question

[bnam]

I have a 74Tii with the Bosch red coil (silver with red label).

While looking for a point to hook up timing lights, I checked the voltages at the coil while it was running.

The stud labeled 1 had about 7V and the one labeled 15 had about 10-11V. Is this what I should expect?

Byas

[TobyB]

errr... sure.

Thing is, the answer to THAT question will depend on your voltmeter.

Because the negative coil wire's actually switched DC, and will vary

depending on how your meter averages.

You will also be able to read AC from it- you'll likely get a number that

surprises you.

t

[bnam]

Aahh!

Ok, next stupid question -- searched on this, but saw so many threads that my head spins---

Does the Red coil (silver with red label & part number ending in 030) on a 74Tii with stock points and distributor require a ballast resistor in addition to the stock resistor wire?

The FAQ says...

"On earlier '02s with a ceramic-block ballast resistor, there is a relay near the firewall that does the bypassing based on a signal from the circuit that energizes the starter solenoid. On '74 and later, they simplified the design and eliminated the relay, instead supplying battery voltage directly to the coil via a second, smaller spade terminal on the starter solenoid (which is itself a relay anyway). Also on '74 and later, the obvious ceramic resistor was replaced by a sneaky, "special" resistance wire that runs in the harness from somewhere over the engine to the coil's positive terminal - it has clear insualtion and a moulded marker at the coil end with the resistance value on it (by now those are usually just a blob of crispy rubber). All resistors for all years were 1.8ohms, according to the factory manual."

But speaking to Rob Torres this AM -- he mentioned that the red coil also needs a ballast in addition to the wire.

Thanks!

Byas

[JohnS]

Look at the positive connection on your coil. If the original wiring is still in place, you will see two wires joined to a single connector on the positive side of the coil. One of the wires is sort of translucent. That's a resistor wire that was used to replace the external ceramic ballast resistors that were used on the earlier cars (prior to '74). That wire serves as the ballast resistor. The resistor wires used on '74 tiis are 1.8 ohm and are all you need to work correctly with a 'Red' coil. Standard 2002s '74-76 also use a similar resistor wire, but with 0.9 ohms of resistance instead of 1.8 ohms. One of my manuals pointed out the difference specific to the '74 tii. Being that I don't always believe what I read, I actually tested the resistance of the wire on my '74 tii and sure enough it tested out to be 1.8 ohms. The resistor wire on the '74 tii runs from fuse #12 all the way to the positive side of the coil. On regular 2002s, that wire is about half as long and ends somewhere about midway in the wiring harness on way to fuse #12. The extra length of that wire on the '74 tii accounts for it having double the resistance of the wire used on standard 2002s. If you want to bypass that wire and run an external ceramic resistor, it's easy because you can just unplug the wire from fuse #12 and run a new wire to the external resistor in it's place.

Good luck,

John

[TobyB]

My father in law lives in Watsonville. Well, a ways outside...

And I NEVER knew that about the 74 ballast wire.

Now we both know something new.

But what I learned actually applies...

hee...

t

[JohnS]

My father in law lives in Watsonville. Well, a ways outside...

Hey Toby,

Small world. I've lived here almost my whole life. If you're ever in the area, let me know. Technically I'm outside of Watsonville proper too. Unincorporated Santa Cruz county. Last night I located the reference to the resistor wire being 1.8 ohms on the '74 tii in my old Chilton's manual for the 2002. That old Chilton's manual was printed in 1974 and has the most accurate wiring diagram for the '74 US cars that I've found. Cheers,

John