Trouble with underhood harness with HEI conversion

[WIDESIDE72]

A while back i bought a new underhood harness for my 72 as the old one was a rats nest. Since i was planning on going with HEI, i bought a harness that is supposed to be "plug and play" from Brothers. I started the truck maybe twide then tore it apart for paint, having never actually driven it. I am putting the teuck back together and reinstalled the harness. I started the teuck fine and drive it about 100 yards and it quit. I checked and have 12 volts at the pink power wire plugged in to rhe dist with key on not cranking. When cranking it drps to 8-9 volts. I had to unplug the pink wire at the dist and hook a hot wire from the battery to the dist to get it to run. Why am i losing voltage at a spot i figured they had researched as having adequate voltage at cranking?!?! On the underhood connector it comes from the far left side second from top.
Posted via Mobile Device

[Bigdav160]

What's the battery voltage while cranking? I wouldn't be surprised to see 10 volts.

That means you have a couple volts of drop in the harness. One tenth volt per connection is considered normal.

I'm a little surprised that the HEI wouldn't fire with 9 volts. Have you checked the spark quality?

[sKnNyPpY]

Sounds like plug and play for a points distributor. The drop in voltage is the same thing the original resistor wire does. 12 v constant is what you want with HEI so you solved the problem just not from the harness point of view
Posted via Mobile Device

[WIDESIDE72]

Originally Posted by sKnNyPpY

Sounds like plug and play for a points distributor. The drop in voltage is the same thing the original resistor wire does. 12 v constant is what you want with HEI so you solved the problem just not from the harness point of view
Posted via Mobile Device

It was advertised as an HEI harness and has the later style connector for the HEI dist, no wires for the coil or points dist
Posted via Mobile Device

[WIDESIDE72]

I dont know how much voltage the hei needs when cranking. Its a new skip white hei with 0 miles. Runs fine with hot wire from battery. Maybe its not the wire harness (?)
Posted via Mobile Device

[sKnNyPpY]

My Skip White is wired straight to the ignition unfused on the fuse block. Maybe your harness connection plugs to something else on the fuse block side?
Posted via Mobile Device

[WIDESIDE72]

Originally Posted by sKnNyPpY

My Skip White is wired straight to the ignition unfused on the fuse block. Maybe your harness connection plugs to something else on the fuse block side?
Posted via Mobile Device

Any idea what the voltage is on the ignition unfused when cranking? Something tells me its leas than 12 volts. I would think the dist would fire with 9 volts while cranking. I have new plugs in the motor gapped at .045...
Posted via Mobile Device

[TBONE1964]

Do you have a DVOM? (digital volt ohm meter) Or just a way to check true voltage drop? Try it directly on the battery while cranking and you will see 9/10 volts while cranking and yes that is enough to lite it up with an HEI. What is the path of the pink wire from the hot side of the distributor. It goes to the junction block and what happens inside? Like others have mentioned, this needs to be on ign unfused. It should have battery voltage when the key is in the on/run position.

Does your ignition switch on the dash have an extra lug for ign? (hot only when key is on) If yes, try and run your pink wire directly to the ignition switch and see if that fixes the problem.

[sKnNyPpY]

Should be 12 v constant. Here's a thread, there are many good threads on HEI conversion with great information. http://67-72chevytrucks.com/vboard/s...d.php?t=536484
Posted via Mobile Device

[Longhorn 70]

bad ignition switch?

[WIDESIDE72]

Originally Posted by Longhorn 70

bad ignition switch?

That was my first thought. I have a wiring diagram and did some checking. I found that on the Brothers harness with hei provision, the pink wire for the dist plugs in to 3A on the firewall power distribution block behind the fuse panel. On the inside, a pink 12 ga wire runs to the ignition switch pigtail to position 3B. The corresponding terminal that this plugs into on the ignition switch is labelled "batt". There is power at this terminal when cranking, verified with a test light. I have not checked how much voltage with my volt meter yet but will do so tomorrow. BTW, I did verify that there is voltage present at the "sol" and "ign" when cranking.
Posted via Mobile Device

[WIDESIDE72]

I am thinking about picking up some dielectric grease to give the connections a better, uh, connection. Everything is pretty dry right now.
Posted via Mobile Device

[WIDESIDE72]

I was thinking about adding a relay to get higher voltage straight from the battery and using the original pink wire oy to trigger the relay. I guess i am not the first one to think of this!:
http://www.hoigto.com/tech/powerHEI.htm
Posted via Mobile Device

[WIDESIDE72]

Back in the 80's when i was a teenager i swapped an HEI into my 71 El Camino. I asked my older brother about using a relay as above and using the old plwer wire with resistor to trigger it and he said it wouldnt work! I proved hi wrong by doing it anyway and driving the car for 7 more yrs before selling it. I havent done an hei conversion since then as everything i have had since then already had one. I didnt think i wod have to bother with it by buying the brothers harness. I guess i was wrong. I still cant figure why it ran for a little while but now won't. Im going to do what everyone always says and "check the grounds!"
Posted via Mobile Device

[WIDESIDE72]

Thanks everyone for the input. I have a few things to try tomorrow. I will keep you updated.
Posted via Mobile Device

[Ironangel]

Originally Posted by WIDESIDE72

I am thinking about picking up some dielectric grease to give the connections a better, uh, connection. Everything is pretty dry right now.
Posted via Mobile Device

Dielectric (silicon) grease is Non-Conductive It is used around electrical contacts and not on them...It is used as an O2 and moisture barrier and as a high temp lube for rubber insulated connections such as spark plug wire boots..."just sayin"

[WIDESIDE72]

Originally Posted by Ironangel

Dielectric (silicon) grease is Non-Conductive It is used around electrical contacts and not on them...It is used as an O2 and moisture barrier and as a high temp lube for rubber insulated connections such as spark plug wire boots..."just sayin"

I used the wrong term. I have some "no-lox" for electrical connections, but even it is really intended for dissimilar metals. I was pretty worn out yesterday!

Someone on an RX7 forum summed it up pretty well:

one thing people have tried is dielectric grease on various electrical component connections. this is NOT a good idea! dielectric grease or "tune up grease" as you may find in auto parts stores is ONLY meant for high voltage connections such as spark plug wires, that is about the only place it belongs on a car.

using it on electrical connections, eventually you may as well pitch the harness into the garbage.. it's almost impossible to get the stuff out once it's in there, dielectric grease does not conduct electricity very well and will in fact cause resistance issues and eventually failed connections.

the best thing to do for connections is to clean and dry them with cleaners like brake cleaner or carburetor cleaner and compressed air. a nice dry solid and sealed connection is about the best you can hope for. any other electrical connector grease compounds are not easy to locate so dry and clean is your best bet.

don't let the name fool you(just put the first 3 letters together and think about it) or let the store clerks tell you otherwise, they're not the ones who have to deal with the aftermath of diagnosing intermittent issues or replacement parts aside from grabbing them off the shelf and ringing them up for you. in fact it's meant as a voltage inhibitor, to keep the spark from leaking out of the spark plug boots and to also keep them lubricated for easy removal.

also seen people use it for the contacts on the notoriously bad window switches, it's at least easy to clean off in there but if you really like tearing the switches apart regularly then go for it.
Posted via Mobile Device
Posted via Mobile Device

[Ironangel]

"The Good Stuff!" http://www.amazon.com/CAIG-DeOxit-Cl...ews/B0002BBV4G

[WIDESIDE72]

While checking grounds I found that the body shop attached the negative cable to the frame so I moved it to the exhaust manifold. I also have two new ground straps from each valve cover to firewall. No paint under screws. Still same voltage and no start with harness plugged in. ??? Looks like time for a relay or pull the skip white dist and install an old oem and see what happens. I wonder if I have a defective module (?)
Posted via Mobile Device

[Zeke's Garage]

Well, if you can get it to run with 12v directly to the HEI, you know three things..
1. The HEI is working just fine
2. The battery should be in good shape. Not too much voltage drop while cranking to affect the HEI module
3. The ground at the HEI is sufficient.

So, that leaves us with the rest of the circuit that powers the HEI. So check the following...

1. The positive lug on the terminal next to the battery that feeds the harness.
2. The interconnects where the Alternator feeds into that power wire
3. The connectors on the harness plug that sends power into the cab, as well as the wire that comes back out to the HEI.
4. The connection to the ignition switch which is where the fuse box gets the 'ign on' feeds

How do all of your other electrical devices work? Headlights, charging system, gauges and such?

I've seen lots of issues with the alternator interconnect wire where it was badly oxidized and the system wouldn't charge, and the feed voltage was low going to the cab.

The only fix for poor connections is to remake them and make sure the wire you're using isn't green or black (oxidized) You may find that you have to replace a good bit of wire before getting to a good clean stretch of copper.

Hope this helps

Shawn

[WIDESIDE72]

Can someone with an HEI tell me how many volts they have at the dist power connector while cranking? More than 10 volts? I would be surprised if fhere was more than 10 volts while cranking. A starter is going to pull a lot. I have 10 volts at the connecteo while cranking which i would think would be enough, but it wont start, leading me to believe its a dist/ module issue.
Posted via Mobile Device

[WIDESIDE72]

Originally Posted by Zeke's Garage

Well, if you can get it to run with 12v directly to the HEI, you know three things..
1. The HEI is working just fine. Not necessarily. It works at 13-14 volts directly from the battery but not at 10 volts
2. The battery should be in good shape. Not too much voltage drop while cranking to affect the HEI module. I have a charger hooked to it since im cranking it so much
3. The ground at the HEI is sufficient.

So, that leaves us with the rest of the circuit that powers the HEI. So check the following...

1. The positive lug on the terminal next to the battery that feeds the harness. Good clean and tight
2. The interconnects where the Alternator feeds into that power wire. Still need to check
3. The connectors on the harness plug that sends power into the cab, as well as the wire that comes back out to the HEI. Good clean tight
4. The connection to the ignition switch which is where the fuse box gets the 'ign on' feeds also good clean and tight
How do all of your other electrical devices work? Headlights, charging system, gauges and such? No idea still putting truck together
And trying to get it to start first. I still have to plug the rear light harness in but the front harness is installed
I've seen lots of issues with the alternator interconnect wire where it was badly oxidized and the system wouldn't charge, and the feed voltage was low going to the cab.

The only fix for poor connections is to remake them and make sure the wire you're using isn't green or black (oxidized) You may find that you have to replace a good bit of wire before getting to a good clean stretch of copper.

Hope this helps

Shawn

Posted via Mobile Device

[WIDESIDE72]

I also bought an adapter to run an internal reg alternator so i am going to check all of that out as well.
Posted via Mobile Device

[Lee H]

Originally Posted by WIDESIDE72

Can someone with an HEI tell me how many volts they have at the dist power connector while cranking? More than 10 volts? I would be surprised if fhere was more than 10 volts while cranking. A starter is going to pull a lot. I have 10 volts at the connecteo while cranking which i would think would be enough, but it wont start, leading me to believe its a dist/ module issue.
Posted via Mobile Device

I think you are on the right track, if I will start with 12 but not 10 it's the distributor.
Posted via Mobile Device

[Bigdav160]

I assume you are checking the voltage at the HEI with it disconnected rather than back probing the connector.

Back probing while connected will give you the true available voltage and can tell you if their is voltage drop in the circuit. Checking the circuit in the same manner toward the battery will likely find the problem.

If you have 10 volts while back probing, I'm with you, something in the distributor (coil) is not right.