1989 new owner, have a question on ignition wiring

[superjay5ive]

Hey guys! First, thanks for such a good source of info! Bought an 1989 4.0 aw4 comanche for a father son project, we have been working thru all of cruisers tips as when we got it, it didn't run the greatest. We have it running pretty good now, BUT we were just about to finish up converting it to an open cooling system and went to start it and we got a no start.

 

While cleaning up the wiring from the PO, was an old amp and some other misc items, I clipped a red wire coming from the cab thinking it wasn't needed. Well it was! This red wire from cab has 12volts when key is on. Its was tied into the larger yellow wire that runs to the Ignition control module. I hooked it back up and it starts. How it was hooked up it did not look factory at all. I assume the original ignition wire was replaced? Digging around a little more I found a cut red wire tucked in some wire loom.

 

I guess my question is it currently works like this, but why would the PO do this? I assume the old wire got damaged and this was the easiest route to get power back to it. Is there any concern leaving it like this? Ill post some pics, I just quickly reattached it to make sure it worked, Ill make a proper wire connection if that is the route to go

 

Thanks

 

Pictures on passenger side.

[Ωhm]

10 hours ago, superjay5ive said:

This red wire from cab has 12volts when key is on.

 

Sure that RED wire isn't HOT ALL THE TIME, including KEY ON?

[superjay5ive]

3 hours ago, Ωhm said:

 

Sure that RED wire isn't HOT ALL THE TIME, including KEY ON?

I'm pretty sure it was only hot with key on. Ill double check here shortly and report back.

[superjay5ive]

Just went out and double checked. Red wire is only hot when key is on, shows 12v. Key off its 0v.

[Ωhm]

RED wire seems to be an add-on wire, not factory. RED is usually HOT AT ALL TIMES. With RED wire disconnected take the following readings:

 

Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage_(B+) on the following pins (use battery_negative terminal for ground):
D1_5:  B+ (Hot at all times)
D1_6:  At KEY ON only (B+ (Hot for 2-3 seconds)).
D2_4:  B+ (Hot during KEY ON and Hot during CRANK).
 

 

[superjay5ive]

5 minutes ago, Ωhm said:

RED wire seems to be an add-on wire, not factory. RED is usually HOT AT ALL TIMES. With RED wire disconnected take the following readings:

 

Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage_(B+) on the following pins (use battery_negative terminal for ground):
D1_5:  B+ (Hot at all times)
D1_6:  At KEY ON only (B+ (Hot for 2-3 seconds)).
D2_4:  B+ (Hot during KEY ON and Hot during CRANK).
 

 

awesome! Thanks, Ill test and report back!

[superjay5ive]

D1_5:  B+ (Hot at all times) THIS IS READING 12v all times

 

D1_6:  At KEY ON only (B+ (Hot for 2-3 seconds)) only getting like .02v with key on.

 

D2_4:  B+ (Hot during KEY ON and Hot during CRANK). same, only getting like .02v On, slight spikes to like .04 while cranking.

 

This was all done using a multimeter with the aftermarket RED wire removed

 

 

[Ωhm]

Two (2) moves here:

 

1) Disconnect C103. On the Engine Harness side, look for 12vdc on pin C103_E (YEL). Turn KEY ON for measurement.

 

 

or

 

Back track wire at D2_4 to Engine Control Harness Splice_F (YEL). Circle with the (F) in it. 

 

 

I suspect NO VOLTAGE from IGN SW (C103_E) at KEY ON or faulty Splice_F.