What the heck are these wires for? --> 1987 Chevy Silverado V10 4x4

[Mike Phillips]

What the heck are these wires for? --> 1987 Chevy Silverado V10 4x4


For some of the regulars, you probably know I had to remove the engine in my truck to get the frame welded up.  See the thread here,

http://tinyurl.com/y7bybvyy


I have the engine installed and about 95% of everything hooked back up except I'm not sure what the two wires in the pictures below are for and where they go?

Could be they are for diagnostics?

I'll post one picture below and make a second post for the second picture to make it easier to talk about by quoiting the individual post.


This wire is coming off the top of the coil?

[Mike Phillips]

Continued....

This wire was poked up inside the box next to where it's coming out but it doesn't look like it was actually connected to any of the pins inside of the box thingamajiggy?



What are these two electrical components and does anyone know what that free floating wire is for and where it should go?

[bd]

Fig 1 is the tach lead.  Unless you have a tach, it won't connect to anything.  However, don't eliminate it.  It can be useful for connecting test instruments or a future tachometer.

One of the two relays in Fig 2 is the fuel pump relay (FPR).  My guess is that the FPR is the one on the right that is disconnected in the image.  The relay on the left has a service replacement pigtail plugged into it (all white wires).  The left relay may be for an optional auxiliary cooling fan or some added accessory.  Is there a ~11" factory caged electric fan in front of the radiator?

Edit:  Both pictured relays have SPDT contacts.  The "free" wire is connected to one of the contacts that isn't used - my guess is the normally closed contact.  The 'free' wire is the result of using a service replacement connector that has one too many wires for the application.

[Irish_Alley]

about the FPR, by the looks of over spray on the one not connected i would imagine they replaced it with the other one and never removed it

[Mike Phillips]

Fig 1 is the tach lead.  Unless you have a tach, it won't connect to anything.  However, don't eliminate it.  It can be useful for connecting test instruments or a future tachometer.

Copy that.

No Tach on the truck.  I'll leave it alone.

One of the two relays in Fig 2 is the fuel pump relay (FPR).  My guess is that the FPR is the one on the right that is disconnected in the image.

The fuel pump works, at least it has worked since I bought the truck.  So has someone bypassed this relay?

 The relay on the left has a service replacement pigtail plugged into it (all white wires). 

Didn't know that... thanks for the info.

The left relay may be for an optional auxiliary cooling fan or some added accessory. 

Is there a ~11" factory caged electric fan in front of the radiator?

No.  There is no caged electric fan in front of the radiator.

Edit:  Both pictured relays have SPDT contacts. 

The "free" wire is connected to one of the contacts that isn't used - my guess is the normally closed contact. 

The 'free' wire is the result of using a service replacement connector that has one too many wires for the application.

Okay, so I'm trying to understand the above...

Does the free dangling white wire need to be attatched to one of the pins inside the relay on the right?

It doesn't look like it was ever attached before but it was bent and pushed up inside the opening on the relay on the right.

When I get over to the truck I'lll take a picture of the inside of the un-used relay.


At some point today I'm going to install the battery and hit the key, if the truck runs and stays running then I guess that means everything that needs to be hooked up is hooked up.

If the engine fires up, (squirt of starting fluid), but does not continue running then this could mean the fuel pump is not pumping and the dangling white wire needs to be attached?

Note to self - never buy anything this new again.  Stick to old school carberated, HEI engines with NO onboard computer.

[Mike Phillips]

about the FPR, by the looks of over spray on the one not connected i would imagine they replaced it with the other one and never removed it

Even though the bracket looks factory, and has places to attatch two relays?

?

[ehjorten]

As BD said...that wire coming off of your coil is the tachometer connection.  The wire coming off of your Fuel Pump Relay is the Fuel Prime wire.  In stock form it would have had the same connector on the end of it as your tach connection.  This connector is a test connection to manually operate the fuel pumps.  It may be powered directly from the battery to run the fuel pump while the engine is not running.

I know in the service manual it usually shows the FPR on the inboard side of that 2 relay bracket, but on mine it is on the outboard side and I believe the wiring diagram book shows it that way.

The relay for the auxiliary fan is mounted on the LH inner fender.  The relay next to your Fuel Pump Relay would have been used for the DRL option I believe, but I will have to double check my wiring diagrams when I get home.  It is a relay for one of the RPOs.

[Irish_Alley]

about the FPR, by the looks of over spray on the one not connected i would imagine they replaced it with the other one and never removed it

Even though the bracket looks factory, and has places to attatch two relays?

?

yes, on my 91 it has one relay but another spot for a second relay on the same bracket. but the short lead is normally red with a spade connector.

[bd]

about the FPR, by the looks of over spray on the one not connected i would imagine they replaced it with the other one and never removed it

Even though the bracket looks factory, and has places to attatch two relays?

yes, on my 91 it has one relay but another spot for a second relay on the same bracket. but the short lead is normally red with a spade connector.

If the engine starts and runs with the relay connections as pictured, then I agree with Irish and ehjorten, the original fuel pump relay was abandoned and a new relay with new connector was installed on the blank hanger of the factory bracket.  In that case the dangling wire is the Prime or Test lead that connects directly to the fuel pump through the relay normally closed contacts.  You can install an insulated terminal on the end of that wire and leave it hanging free.  It can be useful for testing purposes.

[Mike Phillips]

Okay - 2 new mystery wires

This first one comes from the firewall as a part of the wires that go to the air conditioning compressor.



?


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[Mike Phillips]

This second wire is attached to the ESC module (I think that's what it's called, see second picture)





?


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[bd]

The loose plug in the second set of pics connects to the AIR Management Valve that attaches to the AIR pump.

[Mike Phillips]

The loose plug in the second set of pics connects to the AIR Management Valve that attaches to the AIR pump.

Thank you sir!

There is no longer any air pump or air management valve, wasn't present when I bought the truck.