This is a 5-tap relay.
How to wire this so the truck ignition wire triggers 12 directly from batt to HEI? Is "87a" the trigger, 30 hooks to bat and 87 is HEI?

 

No. 85 or 86 goes to ground and the other goes to your current key-on power. They hook to the coil of the relay and when power is put on the coil the relay comes "in".

The drawing depicts the "off" state. So, put battery to 30 and 87 to the HEI, just like you said.

 

Like he said..

You can use the wire you were previously using (the one on the driver fender well I assume) that had the lower voltage as the trigger (to contact #85 or 86 depending on which one you use for ground).

Make sure these are good, soldered, water tight connections. You entire ignition system will depend on this relay working right and holding up..

I have the same relay; did you get the pigtail connector for it as well?

The only issue I had with the pigtail is that the wire was smaller gauge than I wanted to use; I ended up not using it and made my own connector

 

No didn't get the pigtail. Good to know on the waterproofing. May put the relay in some sort of container under the hood, or route it into the cab, (got a big hole where the computer harness was) then come back out.
I was thinking of grounding both 85 and 86. Is that an issue?

 

NOOOO! One of those has to be power and the other is ground. That's what makes the relay work.

 

So Battery goes to 30
HEI gets fed by 87
Ignition Power (to trigger the relay) is then 86 and Gnd is 85?

What to do with 87a?
Sorry, not good with electrical.

 

YES!! You don't need 87a. It will be hot when the key is off so protect it. Or, a slight upgrade is to put battery to 87 and HEI to 30. That way there isn't a hot terminal sticking out when the key is off.

Basics in next post......

 

Did you get it running? We went thru this about a month ago. Once hooked up and timed the HEI along with the new non feedback carb it probably runs better now than when new.

 

Thanks Gary, I admit it, I'm dumber that a stump with electrical sometimes.
Yet wired the whole house! 120VAC I get

 

Relay Basics

A relay is made up of three parts:

• Coil: There has to be an electrical coil that creates a magnetic force when powered. In a Bosch-style relay, which yours is, the connections to the coil are 85 and 86.
• Armature: The armature goes through the coil and is held in the off position by a spring, and moves to the on position via the magnetic force of the coil - when it is engergized.
• Contacts: Relays are shown in the "off" position and the common connection (terminal 30 in this case) is connected to terminal 87a. But, when the coil is powered then terminal 30 is connected to terminal 87. In other words, the little arm is pulled down toward the coil.

 

Thank you Professor Gary!

LOL

I know that my 85 4.9 runs MUCH better with the DUI (HEI) distributor and non-feedback carburetor.

Of course redoing the interior helped also..

 

I missed my calling as a teacher.