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I read the thread...but maybe missed it. I see no mention of the wattage spec of the bulbs used. You have to know that. That style of bulb comes in at least 18W, 12W, 3.7W and 2.7W. THOSE figures are dependent on the voltage listed...which varies from 12.8-14V. The color (K number) will...

Have you looked at the backside of a ballast resistor? Definition: A mixture of coarse and fine aggregate... Obviously the correct define. It just has a few extra wires attached to it.

Got the tach apart. The bezel is simply press-fit to the body of the tach. It didn't want to come apart happily. I could see, maybe, some damage on the PCB...expected. Getting to the PCB was fun. There are three plastic stand-offs seeming to hold it together, but releasing (a squeeze) them...

Nope. This has nothing to do with trying to fix anything, but, is it a common advisory to NEVER change wiring to a tach with power on/engine running? Yes, that is common sense, but do tach installs generally have that noted in RED? ..a brain fart: It's a Mallory that I took OUT awhile back...

Did that. It's not stuck. While it is certainly possible that taking the connection apart with the engine running has nothing to do with the current 'no workee' state of the tach, it would be a strange coincidence. I don't think those happen often. One may not understand or fathom the...

This is all stuff that has worked for many years...nothing new about it. Ignition is a 4-pin LX-101 box. The tach works off the negative coil terminal as with any 'normal' ignition of the period (it's a '73 car). I ran an MSD box for 20 years and, yes, the tach signal was separately derived...

This is a general question that others may hopefully relate/respond to. I have a Mallory tach with a shift ID light. Nothing fancy. The wiring to it has been iffy for some time... a mis-match of connectors fit together and wrapped with Scotch-88. I wanted it easily separable dealing at one...

...but I'll give it a shot. Using an ignition spark tester along the lines of a MacTools ET3142 and an OEM style Mopar ECU, what voltage is measured in your spark plug wires at idle? Or, choose an rpm. A whole lot of things make a difference in that measurement...including what the...

Yes, the ballast has been around the block discussed a few times. I'm sure I've not read all of the threads. Given (from Demon408 years back): and (from killer6 of the same vintage): Engine speed change will take place at the drop of a hat...or the foot. Point is, it happens quickly and...

Yes, this is an old thread. A final result is better posted here (sez me) that an isolated new post, so here are some facts for y'all. I was looking for re-curve information to hopefully resolve a bit of rattle (detonation) I've had for years. It happens right around a best-fill cylinder...

As long as we're almosting and close-ing... When referring to the 5-pin ECU as having a reduced voltage supplied on Run through the 5-ohm side of a dual ballast, keep in mind that pin-1 on both the 4 and 5-pin ECUs is also/still supplied with system voltage. Also, in the interest of...

That is what I see happening, yes. (With a few exceptions: Start voltage is well below static battery (12V) voltage due to starter operation and Run is well over battery voltage due to alternator (14 or so V) output.) IF...it is considered important to feed a 'full' available system voltage...

This thread got off-track and sidewise. To the extent I obscured the matter or was unclear originally, I'm sorry about that. Re: 4-pin or 5-pin ECU? Doesn't matter. Both are the same in regard to the question. Re: 4-pin (dual) or 2-pin (single) ballast? Doesn't matter. Both are the same...

I said, 'Almost' not because anything you said is incorrect, but because part of what you wrote does not apply to the question. Re: Yes. On Start, the ECU is fed through the coil compensating ohm resistor. This part, 'During run, voltage is reduced...by the 5 ohm resistor' is true for...

Almost. During 'start', available voltage (battery, through a switch, through a bunch of wire) is supplied through the 1/2 ohm or compensating resistor. A basic ignition 2-pin ballast pic is attached. Not what you find on a '73, but the wiring in question is shown. During Run, system...

This question 'fits' both 4-pin and 2-pin ballast setups. I understand the purpose of the 4-pin ballast, the higher resistance feeding a reduced voltage to a five pin ECU. The coil compensating side, whatever value it may be, is relevant to the question. The IG2 (start) wire feeds the coil...

If that's a concern, check it like you would a hypoid setup. Put some marking fluid on the flywheel/starter, pull the coil wire, crank it for a bit, check the pattern. Pretty easy to do that on a manual trans car; you have an inspection cover built in for the purpose! If you can separate the...

Did this get fixed? Questions are good. Answers are better!

Yep. Which is why getting your body parts on either the coil- or the ignition module TO3 case when the car is running is going to hurt. 'Magic smoke': I don't want to see that! I used to have a can of smoke to use if bad things happened and it got out. I used it all, don't have no more.

Not to confuse the issue for you, but post#9 had mostly to do with ignition wiring, not starter wiring. If you have a no-crank problem, you aren't to a place you have to worry about start/run wiring ignition-wise. As noted, those comments were 'asides', something that may be useful to you in...

Retro or flatpacks...there is still the need that the input to a tach be dialed down. I've not measured what's on the coil- of the Mopar system, but it's hot enough (high voltage) to make you take notice! No way that kind of voltage is going to be running around in a tach. Pretty good chance...

The starter relay does that. You don't hear it when the starter works..and makes noise. An aside: For working on ignition wiring..maybe chasing down start/run ballast resistor problems, remove the 1/4" screw that holds the starter solenoid wire onto the relay. Be careful...it's close to that...

That is a great point! I've had the tach apart to resolder everything I could get to in an attempt to 'fix' it. No reason I'd recall a resistor on the signal input line...wasn't looking for such a thing. What I do recall being inside the tach: A LOT of flatpack ICs! I could not have guessed...

Perfectly reasonable why a tach attached to coil- would/could screw up anything in the ignition system. My VDO is maybe just behaving for the short-term. It's been flaky for years, every time I've tried it (hoping something fixed itself) it's been flaky...with the blue box. I'll think...

I've been running a 'blue' ignition box for a few years. Got it from the bay. I don't know what it is or where it came from. It works, the car ran fine. I have a VDO white-face tach that I am fond of. The thing started getting flaky a couple years ago. The needle would jump around at lower...

Battery must be known good. I'm not sure about a '71, but my '73 has the starter relay on the left (driver) inner fender. Emergency brake on hard, car in neutral, key OFF, use a flat blade screwdriver to short the starter solenoid connection (bottom of relay, toward front, 1/4" screw with a...

Again...not looking to fix anything. I am aware that a good ground is a necessity, but that's a problem that doesn't need to be solved here.

The one failure I had 'in use' was NOT a 'for sure' unit. Not sure where it came from. It was on the fender for years doing nothing when I was running my MSD box. The second failure was DOA..some supposed NOS (NOT Mopar) piece. 'Proper' ballast. They do vary in actual measurement, but...

The last two I've bothered looking at after they quit had at least one similar symptom: The distributor + pin measured short to ground (case). I'm curious to what extent others have found that to be true. Anyone bother looking at failed modules with a meter to maybe find the same issue...

Thanks! That matches with what I've understood for years. I just bought a 4-pin module to use as another spare, my last 4-pin replacement having lasted six years: The newly purchased NOS unit (not Mopar branded) did not work. The NOS module I bought did not match make/model/year-wise but...