Almost no lights after engine harness change.

[Silverado81]

Hey guys, sorry I haven't been on in a long long time, had a lot of life happen!
Anyway, I decided to tackle the engine harness on my 81 Silverado as the old one is all hacked up with butt splices, and lack of fusible link at the starter. I ordered one that is set up for the serpentine conversion. One at a time as I disconnected an old connection, then hooked up the new connection working from the wiper motor/washer pump, across the engine, and down to the starter. There is a tan wire headed underneath the cab I transferred from the old harness to the new harness, with the correct connector in the same slot it was in, to the left of the blue wire on the bottom row. Possibly for the fuel gauge sender? I got everything hooked up, no wires left over, and plugged the bulkhead into the firewall. I hooked the battery up, opened the door, noticed no clock ticking, and interior lights did not come on. I thought it was completely dead, and just for the heck of it, turned the key, she fired right up, and all the gauges work(except clock). Choke light stays on now too, until I short the oil pressure switch connector. It was previously hooked to a green wire I haven't had a chance to trace out yet. Oil pressure switch is MIA, Pressure switch connector was dangling, still is, but before the harness swap the choke light would operate normally, it would come on when I turned the key, and go off when the engine started. Next I check headlights, dash lights and marker lights, no go either. I do however have brake lights, and turn signals. All lights worked as they should before the harness swap. HVAC, radio(except backlight), power locks, and windows are fully functional as well. I stared at wiring diagrams until I went cross-eyed. It has to be something simple, any help sure would be appreciated!

 

[GTME94]

The choke light will stay on with no oil pressure switch. The power to the electric choke runs thru an oil pressure switch so the choke doesn't start to back off until the engine is running (oil pressure). Without a switch in there the light will come on.

Sorry, I'm no help on the lights.

 

[Rusty Nail]

Remember that thing about the switched wires in the headlight plug , a while back? Does that help? Lol?

 

[Silverado81]

The choke light will stay on with no oil pressure switch. The power to the electric choke runs thru an oil pressure switch so the choke doesn't start to back off until the engine is running (oil pressure). Without a switch in there the light will come on.

Sorry, I'm no help on the lights.

No problem! My oil pressure switch came in today, and I have a brass adapter ordered to accept both the oil sender, and switch on the way. Napa said my truck didn't have one, but it is right there on the wiring diagram! It does just what you said. At least that portion of the issue will be solved.

 

[Silverado81]

Remember that thing about the switched wires in the headlight plug , a while back? Does that help? Lol?

I must have missed that lesson!! Send me the thread please! Funny thing is everything worked as it should before the harness swap, even the choke light. I have no idea how it was hacked to work, but it did, and plan to get back on it this weekend, I want it right.

 

[theblindchicken]

Sounds like you've got a missing or incorrectly placed ground wire.

Check the plugs at the headlights for the correct pin out. May have the high/low pins switched. Also check the ground for your gauge cluster.. if still nothing, check power coming out of the headlight switch.

 

[Rusty Nail]

That "lesson" was in a thread about headlight 'upgrades' . LEDs or whatever trendy thing kids are into these days....
You can find it, it's not old.

 

[Camar068]

yeh sounds familiar

 

[Silverado81]

Hey guys,
Thanks so much for the suggestions! Here is what I have found this morning after tracing out some wiring. From the plug on top of the alternator, there is a red wire that goes to circuit 2 on the bulkhead upper left side. It has very little power going through it, like 0.05 millivolts. For test purposes I stuck a paper clip where the red wire goes into the bulkhead connector. Then jumped a wire directly to the junction block on the firewall, and power was restored to headlights, dome light, clock, etc. So my question is there something in the alternator that is open, and not allowing power though the red wire to #2 circuit?

 

[Rusty Nail]

Why is that alternator plug blue? I'd start there...

 

[Silverado81]

Why is that alternator plug blue? I'd start there...

I'm not sure, I guess that's what color they were making them that day!? I'm concerned about the red wire, why it only has .05 millivolts to the bulkhead, and how to resolve that issue.

 

[Rusty Nail]

I don't like that blue plug.�� it looks ******. Aftermarket.

The terminal dealy that the red wire attaches to (10mm nut?) - has threads on the other end too, it threads into the alternator.

Disconnect the battery.
Get your 10mm and inspect that red wire.
See if you can "tighten" that stud into the alternator. If you can, the alternator is probably broken. Something happened while you were?

The red wire is grounding out somewhere..It's not hard dude, look.

 

[chengny]

I started to write this a couple of days ago and got distracted. From what I read above, it sounds like you are on the right track - no power on the main RED 2G & 2J leads. Both of these leads are supplied by RED 2H (which is always hot from the battery) via a fusible link - the link is located down near the starter solenoid. Check the fusible link for voltage in and out. Voltage on the solenoid side but not on the engine side indicates that the fusible link is melted.



opened the door, noticed no clock ticking, and interior lights did not come on.

Next I check headlights, dash lights and marker lights, no go either. I do however have brake lights, and turn signals.

Those two statements identify (at least in a general sense) the problem as being with one of the RED 2 main power feeds.

One lead originates at one of the fusible links down at the starter solenoid (the one that immediately splits off into two separate leads) and is run straight to the main harness connector at the firewall (top left corner). The other lead goes to the 2 terminal on the alternator.


You have no power coming through the firewall and into the cab on RED-2J. After exiting the main harness connector - behind the fuse block - RED-J2 splits into two separate feeds. These battery power feeds provide power to two very specific circuits.

1. The BAT bank of the fuse block (serves T/L CTSY & HRN DM fuses and clock)

2. The exterior lighting circuits - other than directionals/hazards & brake lights

 

[Silverado81]

Ok here is what I have for voltages. There is only one fusible link on my harness down by the starter. There are three wires hooked to the starter total, the purple solenoid wire, positive battery, and the wire with fusible link that hooks up to junction block. I have 12.22 volts at the starter side, and to junction block after isolating that wire from the block. Where I get lost is the diagram shows a split after the fusible link. One goes to 2G on the alternator, and the other goes to 2J which is where I have no power to the bulkhead. Kind of seems to be a wiring error in the harness to me. The way 2J is wired on my harness is 2G from the alternator hooks directly to 2J on the bulkhead. Now 2C has 12.22 volts, the stud on the back of the alternator is tight, as well as the wire connected to it, and wired according to the schematic. With my jumper wire attached to 2J from the junction I can restore power to the items not working. The problem with that is when I start the truck, and pull the light switch, I get lights, but also an overcharge situation where the alternator is screaming, and the voltage gauge gets into the upper red zone about 16 volts, so I quickly shut off the lights, and all went back to normal. With no lights on the voltage on the battery is 14.50 volts with engine running. This is my first ever rewiring job, I apologize for my skill level being low on this job! It's a pain cleaning up someone else's mess!

 

[Silverado81]

I started dissecting my old harness, and found 2,2G and 2C are all tied together. The alternator pigtail used from left to right starting at the largest terminal: 2G, next terminal not used, the blue wire from the oil pressure switch was hooked here, and the brown wire in the fourth terminal.