Help me avoid burning my truck to the ground please

[bigben5054]

Hey everyone.  Finally getting really close to firing my 1979 K20 back up after a year+ of rebuilding the engine, transmission and transfer case.  I am now working on electrical issues, which are not my specialty and I am here because I'd prefer not to see all my hard work burn to the ground.  Below are my various wiring issues, any assistance is appreciated.  Also I want to note that I am not restoring this $2,000 beater truck back to showroom condition.  I'm not concerned about wiring things up exactly they way they came from the factory.  I just want it to work, not be an eyesore, and not catch on fire.

1) I switched to a tach cluster which has its own 3-wire harness.  I ran the "tach" wire directly to the "tach" terminal on the distributor.  I ran the "ground" wire to that little ground tree under the dash.  Where shall I run power?  My plan was to just turn the key on and stab a voltmeter into empty slots on the fuse panel until I found a live one, crimp a flat blade terminal on the end of the wire and stick it in there.  But something tells me this is how fires start.  Unless perhaps I use an in-line fuse?

2) Electric Choke.  My Holley carb has an electric choke.  I searched and found a post on this, which says you pull the power from the oil pressure switch.  Problem is, when I bought my oil pressure switch I didn't know this and mine only has one blade terminal.  Currently, I have a wire run in the direction of the fuse panel (see bad idea above).  What is a more appropriate way to wire the electric choke, preferably not ordering a new oil pressure switch unless the one I have wont work altogether?

3) Gauges.  Previous owner put in a bunch of aftermarket gauges and molested all the wiring - I am going back to original.  There were an assortment of loose hanging wires in the engine compartment.  I used an ohmmeter to connect one lead to the end of a given wire, then touched the other lead to all the spots on the main gauge cluster connecter.  Once I saw the meter jump, I cross referenced to a wiring diagram to see what that wire seemed to be tied to.  Doing this, I found wires that seemed to be tied to water temp and oil pressure.  I crimped female blade terminals on them and hooked them up.  Did I go about this the right way?  Specifically, is my little ohmmeter trick accurate or am I way off base here?

4)  Fuel gauge.  Truck has dual tanks.  There is a tan wire coming out of the wiring loom in the engine compartment that heads down toward the fuel tank on the passenger side.  There is nothing on the end of it.  There is the same color wire coming from the area of passenger tank (maybe it goes to the tank selector valve - not sure) headed up toward the engine.  It has a butt connector crimped on the end of it.  My hope is that these two long lost lovers just need reconnected to get their spark back and all will be well.  But once again, my suspicions (and Murphy's law) tell me otherwise.  I read elsewhere that for dual tanks there should be a two-wire lead from the wiring loom down to the tank selector, so things appear to be getting off on the wrong foot.

Thanks for reading.  If you can help me out on any of these issues, I would truly appreciate it!

[JohnnyPopper]

I can offer some help:

1. Tach doesn't draw too much power to worry about heat. Share with a low draw, ignition switched circuit. Inline fuse wouldn't hurt, just match the fuse rating correctly. I.E. if the tach draw is 3-4 amps, use a 5 amp fuse.

2. Choke. look for another ign/switched circuit, like your windshield wipers. Check the amp draw of both, you may have to up your fuse rating.

[bd]

For tach power, purchase an American Autowire 500429 connector kit and use one of the clear connectors and terminals to plug into one of the IGN cavities located along the left side of the factory fuse box.  Those three IGN cavities are protected by the 20-amp GAUGES fuse.

For the OE electric choke wiring and a concise description of function, read through the technical article, GM electric choke operation for Q-jet carbs.  You can duplicate the circuit, less the instrument cluster CHOKE lamp.  Tap ignition power for the choke from the fuse box using a similar approach described previously for tachometer head power.  The electric choke requires a two-prong, SPST, non-grounding switch.





Install the switch into either one of the two oil galley taps located at the back of the intake manifold and down by the oil filter.  The oil galleys have 1/8 NPT and 1/4 NPT threads, respectively, so decide on the location before purchasing the switch.  Run the choke power wire through an unused cavity of the firewall bulkhead connector to avoid punching additional holes through the firewall.  If you want to adhere to the factory wiring color scheme, pink is the GM standard color used for ignition power leads.  Because the IGN taps in the fuse box are protected by a 20-amp fuse, I suggest employing 16-gauge wire.

It sounds like you suitably identified the coolant temp and oil pressure gauge wires using continuity checks and should be okay.

The tan wire running rearward along the right frame rail from the firewall bulkhead plug should come from the instrument cluster fuel gauge.  Verify this by performing another continuity check with your ohmmeter.  The two dangling tan wires that you describe below the cab should splice together.  The second tan wire loops back up the left frame rail and enters the cab through a circular four-wire plug on the firewall before connecting to the dash mounted fuel tank selector switch.  The tank selector switch in the '79 model year actually switches the gauge between the two tanks, as well as, energizes the tank selector solenoid valve.

You can refer to the GM 1979 Wiring Manual for specific details.

[JohnnyPopper]

Or you can do that...

bd, ever the purist 

[bigben5054]

Thanks so much!  I tried starting it last night to no avail.  Backfired once through the carb and another time through the exhaust.  That happened only after I poured gas into the carb vents.  So I think it’s a timing issue, which I think I can figure out.

Gauges seem to be working...the tach jumps when cranking.  I see the choke plate moving.  Fuel shows full tank on one side, then goes way past full when I switch tanks.  Not sure either one is accurate.

Bigger problem for time being is despite a fair amount of cranking, there is no fuel in my fram see through fuel filter.  Dual tanks.  I’ll need to do some looking at the lines, etc., but would a bad fuel selector valve cause no fuel?  Anyway to test the selector valve?

[Mike81K10]

Make sure your fuel tanks are clean of rust. My 81 fuel tanks had bad rust and chunks of rust in the tanks. My whole fuel system was full of rust and one tank would not feed. You can see some of the pics on my rebuild post. Gas today with Ethanal can destroy the fuel system in the older trucks. Decided to change out my tanks and fuel lines, then ended up with a full restoration job.

[bigben5054]

Thought I would drop by and share an update.  As I thought about it further, I decided I messed up and had the distributor 180 out.  So I switched that around.  Poured a little more gas in the carb vents and tried again.  It tried to pop off.  I checked the fuel filter and low and behold it was full of gas now.  Resumed cranking and it fired off and took a couple breaths.  Took another peek at the motor and there was gas everywhere.  All over the distributor, puddled on the intake.  It then dawned on me that I forgot to tighten up the chrome fuel line going into the carb.  Now there's a great way to start a fire!  I mopped up the gas with a shop rag and figure I'll let it air out overnight before I try again.  Progress...and that 2 seconds it ran was GLORIOUS!  Thanks for all the help.

[JohnnyPopper]

Good job! keep us posted please

[bigben5054]

Started it up today and it runs pretty darn good.  I ran it up to about 2200 and was letting it run to break in the cam.  I was checking on the gauges frequently.  Volt gauge doesn't seem to be working, it registers nothing.  The tach is way off, registering about 2000 rpm at idle and just going berserk when the engine is actually at 2,000+ RPM   Oil pressure seems good, pegged at 60 psi.  Temp slowly crawled up until it hit the red after about 5 minutes.  It was also about that time I noticed the radiator was leaking out the fins where I accidentally hit it when pulling the motor.  I shut it down right away.  So I'm going to have to find a new radiator.  My water temp sending unit is in the side of the head.  I've seen some in the intake.  Does it matter?  Also, the way I filled the truck with antifreeze was just filling the radiator until it was full.  I left the cap off while it ran a bit and it sucked way down.  Took about another gallon+ to top it back off.  Is this the correct way to fill with antifreeze?

[JohnnyPopper]

Well, sounds like you broke in the cam and lifters! How does it sound? Any loud clicks or clacks, or worse?

Better in the head, closer to the real temp you need to be worried about.

[bigben5054]

Most of what I have read says that to break in a new flat tappet cam, you need to run it for 20-30 minutes varying between 2,000 and 3,000 RPMs.  I plan to run it another 20 minutes or so when I get the other wrinkles ironed out.  There's an exhaust leak, but otherwise no unexpected noises or issues.  Is it just me, or is it scary as heck revving your brand new baby up immediately to 2,500 RPM and just watching her sing?

[JohnnyPopper]

Scary yes! but best practice of many good motor heads...

One of my guys tells a story of breaking in a '65 Riviera 425

The mechanic said that the engine had to run at that RPM for at least 15 minutes

Unbeknown to anyone, they had the t-stat in upside down

Though they endured helter skelter, the old guy would not back off till the clock ran out.

They managed some how not to blow the motor.

He said after it cooled off and he drove it, it was an screaming animal!

[75gmck25]

I always wondered what my neighbors think I was doing when I was running the engine to break in a cam.  I don't have really loud mufflers, but listening to an engine at 2000-2500 for 20 minutes is probably not pleasant for the folks next door.

For a replacement radiator take a look at the aluminum Champion store brand from Jegs.  I used one of them in my '75 and it cools much better than the old 3 row copper radiator.  I also used a Stewart Stage One high flow iron water pump and high flow 195 degree thermostat.  I could probably leave the truck idling all day in 90 degree weather with the A/C on and it would never get above about 195 degrees.

Stock location for the temp sending unit is in the driver's side head.

Bruce

[bigben5054]

For tach power, purchase an American Autowire 500429 connector kit and use one of the clear connectors and terminals to plug into one of the IGN cavities located along the left side of the factory fuse box.  Those three IGN cavities are protected by the 20-amp GAUGES fuse.

For the OE electric choke wiring and a concise description of function, read through the technical article, GM electric choke operation for Q-jet carbs.  You can duplicate the circuit, less the instrument cluster CHOKE lamp.  Tap ignition power for the choke from the fuse box using a similar approach described previously for tachometer head power.  The electric choke requires a two-prong, SPST, non-grounding switch.





Install the switch into either one of the two oil galley taps located at the back of the intake manifold and down by the oil filter.  The oil galleys have 1/8 NPT and 1/4 NPT threads, respectively, so decide on the location before purchasing the switch.  Run the choke power wire through an unused cavity of the firewall bulkhead connector to avoid punching additional holes through the firewall.  If you want to adhere to the factory wiring color scheme, pink is the GM standard color used for ignition power leads.  Because the IGN taps in the fuse box are protected by a 20-amp fuse, I suggest employing 16-gauge wire.

It sounds like you suitably identified the coolant temp and oil pressure gauge wires using continuity checks and should be okay.

The tan wire running rearward along the right frame rail from the firewall bulkhead plug should come from the instrument cluster fuel gauge.  Verify this by performing another continuity check with your ohmmeter.  The two dangling tan wires that you describe below the cab should splice together.  The second tan wire loops back up the left frame rail and enters the cab through a circular four-wire plug on the firewall before connecting to the dash mounted fuel tank selector switch.  The tank selector switch in the '79 model year actually switches the gauge between the two tanks, as well as, energizes the tank selector solenoid valve.

You can refer to the GM 1979 Wiring Manual for specific details.

I'm not getting any volts reading from any of the IGN slots on the left side of the fuse panel.  All fuses are good.  I could have sworn that when I checked them a month or so ago I had some volts, 6 or 8 maybe, but currently there is nothing.  This is with the key in the IGN position (or whatever it's called in between off and run).  What should I check to troubleshoot this?  Thanks.

[bd]

I'm not getting any volts reading from any of the IGN slots on the left side of the fuse panel.  All fuses are good.  I could have sworn that when I checked them a month or so ago I had some volts, 6 or 8 maybe, but currently there is nothing.  This is with the key in the IGN position (or whatever it's called in between off and run).  What should I check to troubleshoot this?  Thanks.

These are the key positions from fully CCW to fully CW:

• ACCESSORY (aka, ACC) - key rotated fully CCW - key cannot be removed - only certain accessories can be used
  
  
• LOCK (OFF) - key can be removed
  
  
• UNLOCK (OFF) - key cannot be removed
  
  
• IGNITION (aka, IGN, RUN) - key cannot be removed - all ignition and accessory powered appliances can be used
  
  
• CRANK (aka, START) - key rotated fully CW against spring pressure - the starter cranks the engine - key cannot be removed and rotates CCW one position to IGN/RUN if released
  

IGN and RUN are the same.  In between OFF (LOCK) and IGN (RUN) is UNLOCK.  You need to rotate the key to the IGN (RUN) position in order to power the IGN cavities in the fuse box.  If you measured only 6-8 volts previously with the key in the IGN/RUN position, either the battery was dead or there is serious resistance in the primary wiring/ignition circuit.  Once you establish power to the fuse box, recheck the voltage available from the fuse box IGN power taps.