HEI and 12V
 

My truck starts like clockwork since the build de-bugging.....At least that's what I said until this morning.

Went out to set up for a headlight adjustment I'm going to do later tonight.
Crank, crank, crank. No fire. Moved the HEI to a little more "retard". No fire.
Crawled up and checked the carb for "squirt". Had "squirt".

Decided to check the connecter at the HEI for 12v. Who knows? Pulled the connector and checked with the key on.
12.65v. Checked the line back at the fuse block at the engine side of the fire wall. 12.56v +.

Checked both places while cranking. Got somewhere around 9.5v DURING the cranking, jumping back to 12v or so with
the key on after I stopped cranking.

I made a jumper and went direct from the HEI to the battery and it started right up. So, I didn't get a chance to check
the voltage during that cranking.

For the purpose of the test and diagnosis, I was concerned that I may have made a better connection at the HEI with the jumper than the stock harness had.
So, I went back and re-connected the stock harness. Fired right up. Of course, I could have made a better connection that time with the stock harness, too.


Here's the question:

Should I get a lower than 12v reading WHILE CRANKING at the HEI connector (while disconnected from the dizzy for the test)? I also got roughly the same drop
from 12.5v + to 9v + during cranking, checking at the fire wall connector while everything was first hooked hooked up and she wasn't starting.

Maybe I'll have to start carrying this puppy....;)

Re: HEI and 12V
 

To answer your question, yes the voltage drop you see down to 9 / 9.5 volts is normal while cranking and should go back to 12 + with key in the on position. You should see around 13 - 14 volts running.

I would chalk this up to a bad connection at the connector to the distributor. I would clean it and make sure it is locking in the coil cover the way it should and call it good.

Re: HEI and 12V
 

What he said sounds spot on to me

Re: HEI and 12V
 

If i read corectly you are using the stock harness to run HEI, the stock harness uses a resistance wire. When converting to HEI you need to run a new wire to the fuse panel.
Someone will correct me if I am wrong.

Re: HEI and 12V
 

To add to my first reply, also make sure the wire itself is good in the terminal and not barely hanging on. I would even add some solder here for added insurance.

Re: HEI and 12V
 

I could be wrong but I don't think he would have 12 volts at the wire if it was resistance wire. The resisted voltage should be around 5 volts for a point type distributor.

Re: HEI and 12V
 

Can you clarify where your supply voltage is coming from? Is it the firewall block and the original resistance wire from the ignition switch? This was a cloth covered wire colored pink,orange and white, but it looks white after all the years have gone by.
Even though there is a resistance in the wire a static measurement of voltage will show battery voltage 12.5 unless a voltage drop test is done between the key switch ignition terminal and the distributor Bat terminal with the wire connected and the key on or cranking.
The voltage drop you are seeing of 9 volts while cranking is battery supply voltage from the source AKA the key switch ignition terminal, which also supplies voltage to the fuse panel and the dash panel.
If you have not removed the resistance wire then you will get less distributor supply voltage and with a poor connection at the distributor it may not start. I have to agree with TBone that you probably had a bad connection there to begin with.
A good place to supply ignition voltage from is the fuse panel ign-unfused terminal with a new 12 gauge wire directly to the distributor.

Re: HEI and 12V
 

Check and see if you have 12v while you are cranking some switches do not have voltage in crank position That is what the yellow wire that went to the starter was for Run new wire to ign terminal in fuze box

Re: HEI and 12V
 

Thanks, Guys.

I have a new M & H harness (engine and under dash), having given them the specification that I'm using an HEI.

But, from reading your responses, I think there is the possibility of couple of things at work here. M & H is so good about "bone stock", that they may not account for the HEI in the harness.
The other possibility is the one you all suspect because of it's "only once and a while" aspect of failure. That is, the wire/contact/terminal to the HEI could have issues.

I'm going to take all of your advice and run a nice, fat red wire from IGN Unfused on the fuse block straight to the dizzy. I'' solder and squeeze until it is as solid as a railroad track!!!!


Thanks very much to all.

Re: HEI and 12V
 

Sounds like a good plan. Nice engine compartment by the way.

Re: HEI and 12V
 

Clean engine bay looks real good Mag. I was worried about that resistance wire also in my sons truck. I have a question though for those who replied and sorry to hijack the post. I removed that cloth covered wire at the engine harness plug and ran a 12 gauge wire in its place that will go to the HEI. My question is is that all that was needed? I did not have to change anything on the other side of the firewall correct? I have not tested the voltage yet as I am still cleaning up other wiring.

Re: HEI and 12V
 

Done deal.

I went out and ran a biggie from the HEI to one of the two Ign Unfused terminals on the fuse box. Had to double up on the one terminal on the left using a female to double blade,
as I was already using both (one for elec. seat and one for elec windows) of the Ign Unfused. Since I won't use the seat and the windows at the same time, and anyway, I have
them both with additional and separate fuses.

I wanted a good connection there. And with the fat wire, I was out of female "blade" connections.
I found a good connector on an old harness from a lead that would be the power to the horn relay.
Snipped it, soldered the wires, shrink wrapped it, and I'm "gone to town".

I'll probably run this little box later when I feel like making a day of it.

Thanks to all of you for your help.
I really appreciate it.

Re: HEI and 12V
 

That is perfectly fine as many others do the same thing. The resistance wire doesn't start until the engine side of the firewall block . See diagram.

The pink wire 5 down from the top to the lower left inside of the firewall connection block. It tees part way down to feed the fuse panel power for the dash gauges.

Attachment 1069124

Here is the pink to the ignition switch again 5 wires down going to the ignition terminal on the switch.

Attachment 1069122

Here is a pic of the engine side of the firewall block and the cloth resistor wire is next to the purple wire on the top. The purple wire is for the starter solenoid.

Nice engine bay from me too Mag. reservations on the personal picture though.:lol:

Re: HEI and 12V
 

Perfect thanks. Yes I need to create a thread to show how the truck was originally wired . All gauges worked but he had only 1 hot wire from the alt to to the factory type splice where it met the hot wire from the junction block on driver side near core support. At this soldiered splice the external regulaters red and brown wire were connected.
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Re: HEI and 12V
 

Thermoquad?!?!

Those were actually pretty good carbs, but you hardly ever see them on non Mopars...

Re: HEI and 12V
 

If you're asking me, Wideside72, that's a Street DeMon. Not the best carb I've ever had. But maybe better than the one I took off, I think. Jury's still out.

VetteVet, CopperC10 and TBONE: Thanks for the nod on the engine bay. There seems to be a lot of stuff hanging off of the passenger's side. I guess it's the cost of
installing air conditioning in a standard trim provided by Vintage Air. But, I'd rather have the hoses than wear a sweat band. It gets nasty here in August.

Also, VVet, I apologize for the bad personal pic. It's an old one.
This one is more current:

Re: HEI and 12V
 

No no just ribbing you LOL.I have seen that one before.

Re: HEI and 12V
 

The red wire yes, the brown wire comes straight from the key switch through the firewall block to the external voltage regulator. Wired to the splice it would be hot all the time and back feed the ignition and fry the coil and points or drain the battery.

Here is the diagram showing the splice and the battery connection to the splice.

Attachment 1069161

here's the inside of the cab showing the brown wire coming through the firewall and heading for the key switch. it is a resistance wire at this point and it takes the place of the idiot light charging bulb in the idiot light dash. I tis the fourth wire down from the top of the diagram.

Attachment 1069162


Here is the complete engine side of the wiring showing the tee and the battery gauge fuses circled in red.

Attachment 1069163

And here is the brown wire arriving at the key switch. At the top of the diagram.

Attachment 1069164

Re: HEI and 12V
 

Vettevet you are the man! Thanks big Time!

Mag I really like the black, chrome and aluminum look. Really nice
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Re: HEI and 12V
 

you could use a relay to power the ignition. Then you wont have any voltage drops.

Re: HEI and 12V
 

I just might have to do that if I don't get an adequate connection with the old harness. Thanks

Re: HEI and 12V
 

maybe you should try a thermoquad!:lol:
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Re: HEI and 12V
 

subscribed!

Re: HEI and 12V
 

I have this exact harness from M&H for my 1972 GMC. I ordered a stock harness with the provisions for an HEI instead of points. I have not had one problem with the setup as installed the way I got it from M&H. The wire for the HEI drops right out of the gutter in a stock appearing location. I've never checked the voltage to it... but I run an MSD Pro Billet HEI with a Digital 6AL box as well...

Gary

Re: HEI and 12V
 

Yeah.

I checked this morning and the wire VetteVet pointed out on the engine side of the fire wall connector is not a "wrapped" wire on the M & H harness. For those who order stock set ups...meaning without HEI....
I suppose they'd provide the resistor wire. But I'm not sure on that, because every time I've used the M & H harness, I've used the HEI.

My check of the connections, etc. was made more problematic by the fact that I'm a strange mod person. And, because of that, I sent the top harness wires back into the cab to "hide" them.

;)

All bets are off on that now, having run the HEI Bat wire directly to Ign Unfused.