Hello! New member here. I’m a guitar builder and repair man, not a mechanic by any means. I had the chance to get the truck we camped in as a kid from my dad and I took it, so bare with my ignorance, please I recently revived my family’s 1966 GMC 3/4 ton pick up, (with a cab over open road camper and all). It hadn’t run in about 33 years. Worked on it over the summer, got it running and drove it the short 5 minutes from my parents to my house. It made it fine. I was replacing things as I went, carb rebuild, fuel pump and fuel filter, thermostat, master cylinder, bled breaks, etc. I was just taking it around my neighborhood every few days to keep it moving and one day it started stalling out on me and acting like it was starved for fuel.I barely made it home. Since then it tries, but has not started. My first thought was I didn’t clean fuel tank well enough, so I’ve replaced the fuel tank and all the rubber line, as well as blowing out steel lines with compressed air, put an in line fuel filter, carb is getting gas. So I did a tune up, all new plugs, points, coil, condenser, rotor, wires, cap. Still wouldn’t start. I’m not getting blue spark, orange weak spark. Just installed high power alternator, and pertronix electronic ignition, and came across this resistor wire! Is it possible this has been my issue all along? I’m going to install the pertronix power relay that bypasses the resistor wire, it’s on its way. Any input would be greatly appreciated. I’m very much a novice. Thanks! - Jimmy
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
Welcome Jimmy. Those camper trucks are good to save. Likely some extra options on that truck. We need pictures.
We will see what the engine experts have to say, but it sounds like you are hitting the right chords. Confirm you cleaned the small filter in the input to the carb. My first thought is fuel, but if you cleaned and checked the tank, lines and carb then we shortly can check that off the list.
~ HB 1966 Chevrolet K-10 | Ghost: formerly Flappy Fenders | In the Stovebolt Gallery 1962 Chevrolet C10 1962 Suburban
Take everything off that is associated with Pertronix. Go back to original or get a GM HEI with the coil in the cap. Some have good results with Pertronix but a significant amount of folks don’t. Weak orange spark won’t do it.
Martin '62 Chevy C-10 Stepside Shortbed (Restomod in progress) '47 Chevy 3100 5 Window (long term project) ‘65 Chevy Biscayne (Emily) ‘39 Dodge Business Coupe (Clarence) “I fought the law and the law won" now I are a retired one! Support those brave men/women who stand the "Thin Blue Line"! Hug a cop! USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
Thanks for the replies. To be fair to the Pertronix, I had weak orange spark before I put it in. I will wait for the relay to get here and try it, if that works, i will assume the resistor wire was my problem. If not, I will remove it all. I appreciate it. I have a couple knowledgeable friends here in Albuquerque, but I’m mostly experimenting, learning as I go.ðŸ‘ðŸ»
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
Here’s a picture of the truck. Unfortunately, my parents used the camper as storage for years, and there were leaks they didn’t know about. There is quite a bit of water damage and mold, so I am probably going to get rid of it once the truck is running, and just keep the truck.
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
Ditto on the "trash the Pertronix" advice. I'm not aware of a factory HEI distributor that will replace a 305 V6 distributor without some pretty extensive machining, but there are two types of Pertronix units- - - -the ones that have failed, and the ones that are getting ready to! A hot blue spark is only necessary if you want to replace distributor caps and rotors on a regular basis. If you're using resistor type ignition wires (a good idea) a normal spark will be orange/yellow looking. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The dreaded "replaced everything but still won't start". It is true there is no drop-in HEI for these motors.
They use a bypass resistive ignition system as do most 12V points motors of the day.
I will have about 5-10 questions when you are ready. Test the battery or get a new one pretty quick.
Take off the camper and take off the spare from front before I go nuts . Hopefully they kept the tailgate. Keep the mirrors, they can be worth money. This is a really good truck with a good motor. Long lasting, powerful motor. I like them for a daily driver truck. But the motor is a boat anchor. I say that with all respect to GMC engineers. The motor is a design masterpiece. Except it's maxed out at 3800 RPM. Approaching 900 lb weight without trans. 60-66 GMC's are fairly rare, especially if it has factory options. Yours seems to be a non deluxe variety. That's OK. The originality of your truck makes it very valuable to some folks, so keep that in mind with all your changes. The GMC crowd is very loyal. 1966 is a premium year. Last year for that body style.
Pertronix is OK. Not necessary, but OK. The newer II and III are better than the old Ignitor I. THE "POWER RELAY" IS A 100% SCAM. If it works, it means you did not install the Pertronix correctly in the first place.
Last edited by bartamos; 02/27/20216:09 AM.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
Battery is new, 4 months old, and is reading 12.6v on a meter.
Tailgate and mirrors are long gone. It was purchased with the camper on it from an Albuquerque dealer who packaged them that way. Had badges made for the side that say "Camper Liner". Dan Ely Buick.
I will take the spare off when I take the camper off. Thats one of the old split rims. It has new wheels and tires now.
The Pertronix I installed is a II.
So far I have not changed anything that can't be changed back to original, and I'm keeping everything I take out for the time being.
Fire away with your questions.
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
OK Jimmy, lets get her figured out. You said you had "yellow spark" before and after the Pertronix. Please be sure to answer every question carefully and thoroughly. 1. You said new coil. When was new coil added? During the points ignition testing or when Pertronix was installed? Did this new coil come with the Pertronix or is it one they recommended? or is it just a generic coil? What words appear on it? What do you know about it's specs? 2. What did you do with the resistance wire? What, if anything, is it wired to right now? 3. Are you saying the starter turns over the motor at a good rate? Is the yellow spark seen across a removed spark plug during cranking or ? 4. Did you, at any point, take out the distributor? 5. Did you add any "ignition" wires? or starter wires? or any wires? 6. What do the Pertronix instructions say about the resistance wire? Did you adjust the gap on the Pertronix to .030 for sure. 7. Is there absolutely no fire when cranked? No backfire at carb or tail pipe? No attempt to start at all? No sputter or odd noise? 8. Can you post good, well lit, clear pics of the distributor and it's wires before you disturb them or add this "relay"? Can you describe exactly how the Pertronix unit and the ignition coil are wired now? 9. If there is a special Pertronix for V6, did you get the correct unit? What is the Pertronix part number?
Feel free to post any other pics of the motor.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
1. You said new coil. When was new coil added? I added a new coil during points testing, it was an OE Driveworks from advance auto, part #26189 I tried swapping it back for original coil, and there was no change. I have since installed the Pertronix flamethrower coil to go with Ignitor II
2. What did you do with the resistance wire? What, if anything, is it wired to right now? It is still wired in place, to positive on coil, and goes into wiring harness. I believe it goes to starter and to plug in firewall. I have not tried turning it over more than once since Pertronix, because wire is not yet bypassed. I tested new alternator, just to make sure it was in correctly.
3. Are you saying the starter turns over the motor at a good rate? Is the yellow spark seen across a removed spark plug during cranking or ? Yes, it sounds like it is turning in over at a good rate, although my only other thought of a culprit is the starter. Yellow spark seen from a spark plug wire removed at cranking.
4. Did you, at any point, take out the distributor? no
5. Did you add any "ignition" wires? or starter wires? or any wires? no
6. What do the Pertronix instructions say about the resistance wire? Instructions said to remove resistance wire or install relay. I opted for relay incase I had to put it back, and because I don't want to slice up the wiring harness.
Did you adjust the gap on the Pertronix to .030 for sure? as best I can tell, I used the feeler gauge.
7. Is there absolutely no fire when cranked? No backfire at carb or tail pipe? No attempt to start at all? No sputter or odd noise? no backfire, occasional sputter like it wants to start.
8. Can you post good, well lit, clear pics of the distributor and it's wires before you disturb them or add this "relay"? we got a snow storm last night, so as soon as it warms up this afternoon, I will take pictures.
Can you describe exactly how the Pertronix unit and the ignition coil are wired now? I followed Pertronix directions exactly, their leads from unit come to ground and positive posts on coil, and the yellow wire and resistance wire are also on positive post for coil. inside distributor there is a ground to plate, and the unit itself.
9. If there is a special Pertronix for V6, did you get the correct unit? What is the Pertronix part number? Pertronix part number is 36-2945 Ignitor II for 6 cylinder, I didn't think of that, I suppose it could be for inline 6?
Feel free to post any other pics of the motor. Albuquerque snow doesn't last long, I'll update with some pics later today.
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
@ no. 3 answer...........describe "spark plug wire" test. How was this test done exactly. What do you mean by spark plug wire? Where was the spark plug? What part of what wire? at plug, at distributor?????????? From what to what did the spark jump? How far did it jump?
@ No. 8 answer.............what is the yellow wire? What color is the resistance wire?
Have you installed the relay?
36-2945 has NO matches on google or the Pertronix website????????????? PLEASE PROVIDE LINK. Search brings up 1162A for L6 and V6 GMC. Maybe your number is superseded or you are giving a vendor number. Where did you buy it and how long ago?
The alternator has nothing to do with starting.
Do not disturb any wiring until I get done thinking and asking and seeing pics.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
The first thing I would do is ELIMINATE the truck wiring system. Make a 12g jumper wire to run from battery + to coil +. If spark color improves or if it fires and runs good then trace down the trouble. We also have a freon jug gas can with a regulator so pressure can be set from zero to 150psi to cover both carbs and fuel injection. This eliminates the factory fuel system to isolate the trouble if there. KISS
[ no. 3 answer...........describe "spark plug wire" test. How was this test done exactly. What do you mean by spark plug wire? Where was the spark plug? What part of what wire? at plug, at distributor?????????? From what to what did the spark jump? How far did it jump? The ol' screwdriver in the plug wire, (at the plug end, not cap), make it arc to metal on the engine.
@ No. 8 answer.............what is the yellow wire? What color is the resistance wire? I can't find the exact wiring diagram for that truck, but I believe the yellow wire comes from the starter, and the resistor wire is clear insulation with a visible braided wire shielding below.
Have you installed the relay? I don't have the relay yet
I know alternator has nothing to do with starting, I was making sure it was wired in right and belt was tight. I won't disturb any wiring, and will have pics soon. thank you
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
You forgot to answer about the part number 36-2945.
1. As a point of info: On a 66 GMC there was one wire from ignition "on" terminal to starter "R" terminal. This was the resistance wire. Then there was a yellow wire from the "R" terminal on the starter to coil positive.
2. The Ignitor II instructions I have say that you can remove resistance wire or not. Do you agree? I.E. Figure 2.
3. Here is the disturbing part and may be your problem, once I am sure what you said. Regarding the positive terminal on the coil: you said you have the Pertronix wire (probably red), a yellow wire, and the "resistance wire" on that terminal. That would be three wires. Is that what you have or not? Here are your words:
I followed Pertronix directions exactly, their leads from unit come to ground and positive posts on coil, and the yellow wire and resistance wire are also on positive post for coil. inside distributor there is a ground to plate, and the unit itself.
Very glad you are NOT doing ANYTHING until I am done with troubleshooting.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
part number is 91162A Ignitor II for telco 6cyl w vac advance
1. As a point of info: On a 66 GMC there was one wire from ignition "on" terminal to starter "R" terminal. This was the resistance wire. Then there was a yellow wire from the "R" terminal on the starter to coil positive. Good to know. thanks
2. The Ignitor II instructions I have say that you can remove resistance wire or not. Do you agree? I.E. Figure 2. I agree, however it says, 'All external resistors should be removed to achieve optimum performance'. It also says, minimum voltage is 8v, I am getting 5.6 from positive coil terminal. Thats why I was assuming I have to bypass or remove.
3. Here is the disturbing part and may be your problem, once I am sure what you said. Regarding the positive terminal on the coil: you said you have the Pertronix wire (probably red), a yellow wire, and the "resistance wire" on that terminal. That would be three wires. Is that what you have or not? Here are your words:
I followed Pertronix directions exactly, their leads from unit come to ground and positive posts on coil, and the yellow wire and resistance wire are also on positive post for coil. inside distributor there is a ground to plate, and the unit itself. Leads to coil positive are: Red from Pertronix, and one hoop connector with yellow and resistor wire. that's how it was when I got it, and it ran with those wires going to original coil.
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
There are several options. I don't know which you can do. I think you are savvy enough to do what needs to be done. First step: 1. We don't want to mess up the harness or add wires yet if we don't need to SO......... how many wires are on the "R" terminal on the starter? What color are they? 2. 5.6V with ignition to "on"? How did you hook up the meter leads? Where on the truck did you place the leads for the measurement? 3. What is the voltage at the starter "R" with ignition on? FIY: The ignition switch has "Ignition on" position and a ignition "Start" position, which is a spring loaded position. Just so you know what I mean when I say "on"..... I don't mean start.
FYI: There is a big honking cable to the starter, you know that. There is one wire on the "S" terminal. We are interested in the "R" terminal right now. Let me know. A pic or two is nice. It would be VERY helpful if you could figure out where the yellow and companion wire, that you have on the coil, goes. Does it look like someone did that or does it look factory? Don't think it's factory because yellow is so big. At any rate, it's not per 1966 wiring diagram. We will fix that.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
First step: 1. We don't want to mess up the harness or add wires yet if we don't need to SO......... how many wires are on the "R" terminal on the starter? What color are they? based on my pictures, it seems there is only the yellow wire or the R terminal. it goes into a harness, and to the positive. I think its the hot wire. The Resistance wire doesn't seem to be at starter. it comes up the harness to the coil positive, and also seems to continue in harness to plug in firewall.
2. 5.6V with ignition to "on"? How did you hook up the meter leads? Where on the truck did you place the leads for the measurement? I put a jumper from negative post on coil to ground, I put black lead from meter on negative, red on positive, turned ignition to 'on'.
3. What is the voltage at the starter "R" with ignition on? 11.9 to 12. battery reads 12.2 with ignition on.
FIY: The ignition switch has "Ignition on" position and a ignition "Start" position, which is a spring loaded position. Just so you know what I mean when I say "on"..... I don't mean start.
FYI: There is a big honking cable to the starter, you know that. There is one wire on the "S" terminal. We are interested in the "R" terminal right now. Let me know. A pic or two is nice. It would be VERY helpful if you could figure out where the yellow and companion wire, that you have on the coil, goes. Does it look like someone did that or does it look factory? Don't think it's factory because yellow is so big. At any rate, it's not per 1966 wiring diagram. We will fix that. It looks factory, buy I don't know for sure.
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
1. When checking voltage, you just touch the red meter lead to the place/terminal you want to check and touch the black meter lead to good, clean shinny motor metal, body metal or frame metal. You don't add a jumper or touch other posts. If you are testing a component to see if it is bad, there may be different meter hookups. 2. So lets try this again with meter as I described. What is voltage at coil pos with ignition off? What is voltage with ignition on? 3. Someone has tried to wire the ignition from a Chevy diagram or a pre 1964 GMC diagram. GMC changed the ignition wiring scheme a little bit. I just want to check the voltage per note 2 before moving forward with solution. Almost there. 4. Is the coil in the pics the Pertronix Flamethrower? What coil is on the motor now? I don't se any logo on it. 5. Battery is checked with ignition OFF. You said it was 12.6 now 12.2 correct? Recheck with ignition off. The battery is checked across the posts. Red meter on pos post, black meter on neg post.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
The instructions I followed were what was on the literature that came with Pertronix coil, which is what is in the truck. The logo ended up face down, which is fine with me. I’ll check it again in a bit.
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
I am not questioning the Pertronix install when I said somebody wired ignition per wrong diagram. I'm talking about the yellow and resistance wire that was already there. Lets get on with the other tests above.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
It says zero at off. And the instructions I was talking about for Pertronix coil was a test they instruct user to do to check for resistance, not the instructions for install.
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
Take the yellow and resistance wire pair off of the coil and arrange them where they won't touch anything. Leave Pertronix as you have it. Install a jumper from battery positive post to coil positive. Make sure one end has a alligator clip for fast removal. It will be the only way to turn off motor. When jumper is attached, start truck. Ask any questions before starting, otherwise report what happens. BE SURE you are not out of gas in the truck.
I never got a battery reading with ignition off, across posts.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
alright, I sure will. the bad news is, I HAVE TO GO TO WORK AGAIN! Gotta leave here in 15 min. I'm gonna run by electronics store and get some bigger wire and alligator clips, (mine is for guitar and Audio, 22awg), I'll make the jumper at work, soldering iron on my repair bench at all times, and do it when I get home. STAY TUNED Thanks for all the help.
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
Got out of work early so I could catch a little daylight to do the jumper. It did not work. It sounded very much the same as it did before. trying to turn over. I shot a short video of it trying to start, but I cannot load it. Too big a file. Does this point us towards the starter?
Jimmy Deveney ‘66 GMC 3/4 ton pick up 4 speed manual 305E V6
. Hopefully they kept the tailgate. Keep the mirrors, they can be worth money. This is a really good truck with a good motor. Long lasting, powerful motor. I like them for a daily driver truck. But the motor is a boat anchor. I say that with all respect to GMC engineers. The motor is a design masterpiece. Except it's maxed out at 3800 RPM. Approaching 900 lb weight without trans.