Under hood wiring - Part 1

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Scott91370

Full Access Member
Joined
Apr 2, 2018
Posts
928
Reaction score
902
Location
Burleson, Tx
First Name
Scott
Truck Year
1985
Truck Model
Sierra1500
Engine Size
350
Trying to get the truck running this weekend (no spark) but I have several wires that I don't know where they go and I'm having a hard time with the wiring diagrams I have found. Basically they're not dumb enough for me to follow.
First problem is; on the driver's side there is a wiring block that comes through the cab. I have 3 wires that go nowhere from this block, here is a pic:
View media item 8551
Pink - connector:
View media item 8553Green - connector:
View media item 8552Brown - cut, no connector



Second issue I have this on the passenger's side. This pink wire was connected to the coil on the distributor (I think it may be the wrong one since I was not getting spark). As well as all the other wires in this picture, none of them were connected.
View media item 8556
Third issue is another green unknown wire that comes off what I think i the oil pressure sending unit wiring harness:
View media item 8555View media item 8554
 
Last edited:

82sbshortbed

Fuckemall!!
Joined
Mar 1, 2018
Posts
14,828
Reaction score
49,083
Location
SE Texas
First Name
Doug
Truck Year
1982, 1984
Truck Model
1500 shortbed, 1500 longbed
Engine Size
454, 305
I can't see your pics but, if you run a hot wire with key on to the post on distributor that says bat then you should get spark.

If not then at least you've got a direction to go from there.
 

Scott91370

Full Access Member
Joined
Apr 2, 2018
Posts
928
Reaction score
902
Location
Burleson, Tx
First Name
Scott
Truck Year
1985
Truck Model
Sierra1500
Engine Size
350
That worked!
Did that and no spark. Neighbor and friend came over and we traced it to the little black module in the distributor. Swapped it and we had spark. Found TDC for #1, out everything back together and BAM! No spark, again. Not sure what it is now, have a feeling the same module went out but wouldn't have a clue why.

I wonder why the pics don't work. I uploaded them to the site then added them to the post. Hopefully it is only the way you're connected and everyone else can see them.
 

chengny

Full Access Member
Joined
Feb 22, 2012
Posts
4,086
Reaction score
1,008
Location
NH
First Name
Jerry
Truck Year
1986
Truck Model
K3500
Engine Size
350/5.7
Pink - connector:

Green - connector:

Brown - cut, no connector

Second issue I have this on the passenger's side. This pink wire was connected to the coil on the distributor (I think it may be the wrong one since I was not getting spark). As well as all the other wires in this picture, none of them were connected.

Third issue is another green unknown wire that comes off what I think i the oil pressure sending unit wiring harness:

Without images it's hard to visualize what you are dealing with. But just in general:

There are two PNK leads coming through the bulkhead connector.

One is power from the ignition switch to the B+ terminal on the ignition coil. That wire transits the connector at the 2nd row from the top/3rd bay from the right.

The other PNK wire is power to the windshield washer pump. It transits the connector at the top row/3rd bay from the right.

GRN lead. There's only one out of the bulkhead connector. It is the sensing leg for the coolant temperature gauge and connects to the temperature sender (which is screwed into the LH cylinder head between 1 & 3 cylinders). Transits at 3rd row down/1st bay on the right.

BRN lead. It transits the connector block 4th row down/1st bay on the right. It goes to the # 1 terminal on the alternator. In the cab it connects to the alternator warning light or the ignition switch - depending on whether or not you have gauges.

The second PNK wire coming over from the passengers side may well be the power supply to the WSW pump as discussed above.

As far as the other GRN wire; are you sure it isn't the other end of the coolant temp sensing leg? Except for the power to the horns, there are no other GRN leads in the engine compartment - and the GRN to the horns transits the connector block in the forward light section.

Click on the image to enlarge:

You must be registered for see images attach
 
Last edited:

eskimomann209

Full Access Member
Joined
Jan 9, 2019
Posts
1,849
Reaction score
2,000
Location
Modesto
First Name
Marcus
Truck Year
1973
Truck Model
C10
Engine Size
5.3
Can’t see them
 

Scott91370

Full Access Member
Joined
Apr 2, 2018
Posts
928
Reaction score
902
Location
Burleson, Tx
First Name
Scott
Truck Year
1985
Truck Model
Sierra1500
Engine Size
350
Let's see if this works:

First problem is; on the driver's side there is a wiring block that comes through the cab. I have 1 brown wire with no connector on the end that goes nowhere from this block - labeled unknown at the bottom right of the picture. It's not the alternator wire, that one is connected.
You must be registered for see images attach

Green is coolant temperature gauge and connects to the temperature sender (which is screwed into the LH cylinder head between 1 & 3 cylinders).


Second issue I have this on the passenger's side. This pink wire was connected to the coil on the distributor (which we now know is the wrong one since I was not getting spark). As well as all the other wires in this picture, none of them were connected.
You must be registered for see images attach




Third issue is another greenish blue unknown wire that comes off what I think i the oil pressure sending unit wiring harness (not the bulkhead connector):
You must be registered for see images attach


Comes from above plug/harness to this end connector: Electric Choke?
You must be registered for see images attach



Last issue, for this thread, Green Connector:
This connector is in the same harness as the A/C plug. Fast Idle Solenoid?
You must be registered for see images attach
 
Last edited:

Scott91370

Full Access Member
Joined
Apr 2, 2018
Posts
928
Reaction score
902
Location
Burleson, Tx
First Name
Scott
Truck Year
1985
Truck Model
Sierra1500
Engine Size
350
I have now found another connector with a blue wire and yellow wire.
It comes from loom under the truck, driver's side.
You must be registered for see images attach

You must be registered for see images attach
 
Last edited:

chengny

Full Access Member
Joined
Feb 22, 2012
Posts
4,086
Reaction score
1,008
Location
NH
First Name
Jerry
Truck Year
1986
Truck Model
K3500
Engine Size
350/5.7
I have now found another connector with a blue wire and yellow wire.
It comes from loom under the truck, driver's side.
You must be registered for see images attach

You must be registered for see images attach


That plugs into the EGR bleed solenoid - part of the TCC control circuit.
 

Scott91370

Full Access Member
Joined
Apr 2, 2018
Posts
928
Reaction score
902
Location
Burleson, Tx
First Name
Scott
Truck Year
1985
Truck Model
Sierra1500
Engine Size
350
Thanks. I see nothing else EGR looking on the truck so I will find a nice place to tuck it away.
 

Matt69olds

Full Access Member
Joined
Jan 8, 2018
Posts
2,345
Reaction score
3,590
Location
Central Indiana
First Name
Matt
Truck Year
81
Truck Model
GMC 1/2 ton
Engine Size
455 Olds
You must be registered for see images attach
This wire went to the choke heater on the passenger side of the carburetor
 

Matt69olds

Full Access Member
Joined
Jan 8, 2018
Posts
2,345
Reaction score
3,590
Location
Central Indiana
First Name
Matt
Truck Year
81
Truck Model
GMC 1/2 ton
Engine Size
455 Olds
My first thought for this wire was for the temp sending unit, but you said it was part of the A/C harness. That suggests to me your on the right track thinking idle solenoid. The blue wire you mentioned is most likely the oil pressure sending unit. Make a jumper wire with the smallest rating fuse you can find. With the key on, ground the blue wire. The oil gauge should drop to zero, or the light come on. Same thing with the green wire. If the gauge goes full hot (or the light comes on) then you know what that wire does.

the 4 pin connector most likely went to the distributor. If your distributor does t have a matching plug, then someone sometime in the past “lobotimized” your truck by removing the computer controlled distributor and replaced it with a old school HEI.

You must be registered for see images attach
 

Scott91370

Full Access Member
Joined
Apr 2, 2018
Posts
928
Reaction score
902
Location
Burleson, Tx
First Name
Scott
Truck Year
1985
Truck Model
Sierra1500
Engine Size
350
Thanks everyone for all the input! That is all but the one, what appears to be, brown or tan colored wire that the connector was clipped from which could be the alternator gauge wire
that chengny mentioned:
BRN lead. It transits the connector block 4th row down/1st bay on the right. It goes to the # 1 terminal on the alternator. In the cab it connects to the alternator warning light or the ignition switch - depending on whether or not you have gauges.

I just don't remember a #1 marked terminal on my alternator and it's raining so much today I won't be able to double check.
 

Scott91370

Full Access Member
Joined
Apr 2, 2018
Posts
928
Reaction score
902
Location
Burleson, Tx
First Name
Scott
Truck Year
1985
Truck Model
Sierra1500
Engine Size
350
I like that!

I think I now have everything sorted. I think the one I call brown is actually tan and it is for electric choke.
Well, except maybe this group which we think was for the old distributor:
You must be registered for see images attach




Thanks to everyone for your help!!
 

Forum statistics

Threads
42,070
Posts
908,405
Members
33,546
Latest member
Tater81
Top