‘77 620 showing 14V key in on position.. HELP

[H-BRATSON]

My datto is showing 14v when the key is turned to the on position at the ignition coil to a known ground. No spark. Went through a lot of wiring and got the truck to crank and fixed a lot of the body harness already. Really struggling with this one. Recently changed the distributor because the truck required an electronic dizzy and I had a points distributor on it(previous owner). Never had power to the coil before i swapped distributor and fixed wiring. Now it has power but is running 14v. Every time the key is turned to the on position, the spark tester lights and same thing when I turn it off. No spark when it should though. Also note that the ignition relay clicks when the spark tester lights up(when key is turned to on/off position. Help..

[Crashtd420]

Well 2 things jump out at me....

 

First you should check for power at the coil when you turn the ignition to start position not just on.... 

 

2nd how are you seeing 14v with the vehicle not running?

At rest a battery only is 12.5v, the alternator once running brings it up to 14.2 to charge the battery and run the electronics... so 14v isnt bad. 

[datzenmike]

The '77 620 has a points distributor from the factory. Nothing wrong with an RI distributor swap but there are 2 styles, remote igniter and matchbox.

 

The remote igniter distributor looks like this...

 

 

... and requires this 'remote igniter' box mounted in the cab near the glove box...

 

 

 

 

This is a matchbox distributor and the remote igniter box has been miniaturized and placed on it's side

 

 

It would be wired like this if put in place of a points distributor.

 

 

 

So which distributor do you have????

 

[H-BRATSON]

14 minutes ago, Crashtd420 said:

Well 2 things jump out at me....

 

First you should check for power at the coil when you turn the ignition to start position not just on.... 

 

2nd how are you seeing 14v with the vehicle not running?

At rest a battery only is 12.5v, the alternator once running brings it up to 14.2 to charge the battery and run the electronics... so 14v isnt bad. 

Well, kinda working on it by myself.. little difficult to turn the ignition to start and test it by myself.

 

def will try to get a second set of hands to help out with testing. Thanks!

[H-BRATSON]

4 minutes ago, datzenmike said:

The '77 620 has a points distributor from the factory. Nothing wrong with an RI distributor swap but there are 2 styles, remote igniter and matchbox.

 

The remote igniter distributor looks like this...

 

 

... and requires this 'remote igniter' box mounted in the cab near the glove box...

 

 

 

 

This is a matchbox distributor and the remote igniter box has been miniaturized and placed on it's side

 

 

It would be wired like this if put in place of a points distributor.

 

 

 

So which distributor do you have????

 

Well Mike I have the remote ignitor transistor box in the cab and the correct dizzy for it as well. I have kind of a different weird transistor box however.

[datzenmike]

Well someone put it in or you have a '78 truck, the '77 was a points truck. That said the California trucks were the first to get the EI system so maybe a California truck. Look on the driver's door jam for the build date to confirm '77 or '78 and post this information.

 

Better post a picture of what you have.

 

 

With ignition on the + side of the coil will show battery, and this should be under 12.6v. 14v is unlikely and makes me suspicious of your meter.

 

When the engine is turned by the starter the meter or test light should flash (probably dimly) as the EI system makes and breaks a path to ground to fire the coil.

 

 

[H-BRATSON]

It is a '77 verified by build date in door and comparing it to the wiring diagram it's looking like it is indeed a California model based on the ballast resistor used( I believe they used a different one correct me if wrong). I will try to take and upload some pictures when I get a chance. Trying to figure out how to upload images on here since they have to be uploaded via URL.

[H-BRATSON]

Okay really been having trouble getting Images to upload. It is the e12-12a hitachi trasistor box.

[H-BRATSON]

I also got a new meter. Voltage to the positing terminal is 12.1V.went through ignition switch wiring to see if it had been messed with and everything is perfect there. Gone through the harness looking for shorts and i have none. Verified ground. I’m at a loss lol

[datzenmike]

On 12/7/2021 at 7:01 AM, H-BRATSON said:

It is a '77 verified by build date in door and comparing it to the wiring diagram it's looking like it is indeed a California model based on the ballast resistor used( I believe they used a different one correct me if wrong). I will try to take and upload some pictures when I get a chance. Trying to figure out how to upload images on here since they have to be uploaded via URL.

 

Yup has three terminals. Those I know very little about as they are early EI. We can check for obvious faults like a bad coil or lack of power to it....

 

Check positive terminal of coil for power with key on.

Check that there is power while engine is being turned by the starter.

 

If it turns out the transistor unit is faulty there is a cheap alternative for replacing it.

[H-BRATSON]

What would you recommend replacing it with? Also going to have the girlfriend crank it while i rad the voltage at the positive terminal to verify volrage while cranking. And I guess my transistor box is a 5 terminal?? Has black(ground), black white(power from ignition switch), blue(signal?), red and green(terminal contact points for electronic distributor). Do you know about these guys?

[H-BRATSON]

Did a little more research last night regarding the coil, ballast resistor, and box. Found a video of a guy testing his coil and ballast resistor on a Z. I noticed the same ballast resistor and am thinking the ei system may be the same for the 620..:/?