Whats This Electrical Contraption?

[Rob73-87]

Originally Posted by lurch115

if the truck was converted from a diesel to a gas that relay and such would have stayed with the diesel since the diesels don't use a distributor, and they also have different valve covers.... that and the glow plug controller is larger than that relay...

Believe me - GM won`t mount a relay to a valve cover !!!!??? As I said, I have the same relay too, and my truck came with a TH700 - so it can`t be the kickdown-switch....

Any idea ?

[sierra4x4]

I think you may be right f.monroe becouse my 84 3/4 ton 350/Th400 has one and I have a buddy with a twin to my truck (both optioned identical both bought new by a construction outfit) the only differance is that his was a 305/700r4 and his truck does not have it.

[Dezdon]

I looked in my Haynes 67-87 chev/gmc repair manual and couldnt find anything on it. It does look OEM to me. I have seen these over the years.
My suspicions:
Cruise control system
Power steering or a/c activation sensor(when a/c kicks on or power steering, it senses the load and changes something in the RPM or something.
A factory option not being used.
Something to do with emissions?
I'll ask a few old time techs I know next time I see them and post back if I have anything.
But it runs the same with out it?

[JohnC]

Could it possibly be something that only Canadian trucks have? The two that say they have it are both in Canada.

[gchemist]

It's a GM installation. I've seen it posted. I'll try to dig it up or find what it does.

[DirtyLarry]

I will have to eat my shoe if it is proven to be OEM because I don’t believe it is a GM installation for a second. I have had my head of under hundreds if not more of these trucks and have never seen a relay on the valve cover. I just cannot wrap my head around the idea GM would ever mount a relay on the engine of all places. Yes, the reply is a GM relay but that means nothing. The same part number of relay could be used in any circuit that would require a relay…heck you could use the GM relay on a Dodge if you wanted. The harness could look OEM as well if the aftermarket supplier purchased connectors from the Packard (old GM electrical supplier) back then. That happens a lot still today….many aftermarket suppliers use Delphi connectors for aftermarket components for ease of installation into GM products. The turn signal lights on the ARB front bull bar I just bought for my ’05 HD is a good example of aftermarket companies using GM supplier components.

That said, I am 99.9% sure that is an aftermarket dealeo of some sort unless it is something specific to Canadian trucks.

[enaberif]

Why would ANYONE install something onto the valve cover.. that is what baffles me.

[73chevyman]

after looking at your first pic looks like you got a water leak from your bell housing noticed radiator fluid on your intake

[Dezdon]

Now that I look at it, your right, that cant be a OEM install. I would think if GM had something on thier valve cover, it would have a bracket spot welded to the valve cover and raised up off the surface. then the relay would just kinda clip in place.
This thing is just nut and bolted through the valve cover, not a factory engineer style.
What about one of those after market A/C kits, or a snow plow adaptor electric component.

[Dezdon]

Hey, what about one of those old "knox" device kits from the 70-80's from California emission laws?

[Blue85]

Originally Posted by Dezdon

Now that I look at it, your right, that cant be a OEM install. I would think if GM had something on thier valve cover, it would have a bracket spot welded to the valve cover and raised up off the surface. then the relay would just kinda clip in place.
This thing is just nut and bolted through the valve cover, not a factory engineer style.
What about one of those after market A/C kits, or a snow plow adaptor electric component.

If you look close at the pic there is a bracket spot welded to the cover,sits about an 1/8" off, and the stud is welded to the bracket, after thinkin about it I can almost guarantee this had some thing to do with the emissions system that used to be on the truck. Heres what ive figured out on it so far, gets main power from the bat wire goin to the coil, it uses voltage from the tach to activate the relay, mabye it was used to activate a canister purge solenoid when the rpm was in a certain range. I sont really have the tools to check how much voltage the relay opens at, but thats what ive figured so far.

[lurch115]

i just can't wrap my brain around this either....that relay looks like a heater relay to me (for the blower motor) and i just have a hard time believing that GM would mount a relay to a valve cover like that...the constant heating up and cooling down would kill it. especially since it is cased in metal....if i am wrong i am wrong....just going off of what i know from what i have seen.

[lurch115]

okay, now i have to eat my words....if you look at chapter 6 (emissions control systems) page 3 (6-3) of the Haynes repair manual...in the 2nd picture down on the left hand side of the page you will see the relay...but as to what it is or does...still not sure...i'll thumb through the whole book if i have to to find out though....

[rafterman191]

Originally Posted by Longhorn321

You're not on here asking about a F@%d are you?

hehe, I just chuckled at that one.

[ElGracho]

I just looked in my Haynes book. It is the 67-87 Chevy and GMC pickups book. On page 213 and 214 it describes the Throttle Return Control (TRC) system. It holds the throttle open slightly when the engine is coasting. It consists of the wiring harness, the
"Engine Speed Switch" (the thing we are trying to figure out) and the TRC solenoid.

It even shows a picture of the switch mounted on the valve cover on page 214.

I'm sure this is the mystery box...

[Blue85]

I think we have a winner lol!

[Blue85]

BTW here is a pic of the bracket it sits on.

[ElGracho]

Here's a blurry digital picture from page 214, right column. I don't have a scanner...

[Blue85]

You must have an older manual than me, mine is in sections, like 5-12, what section of your manual is it in?

[Longhorn321]

Originally Posted by ElGracho

It holds the throttle open slightly when the engine is coasting. It consists of the wiring harness, the
"Engine Speed Switch" (the thing we are trying to figure out) and the TRC solenoid.

It even shows a picture of the switch mounted on the valve cover on page 214.

I'm sure this is the mystery box...

That would explain the wire going to the dizzy.

[Rob73-87]

Originally Posted by ElGracho

I just looked in my Haynes book. It is the 67-87 Chevy and GMC pickups book. On page 213 and 214 it describes the Throttle Return Control (TRC) system. It holds the throttle open slightly when the engine is coasting. It consists of the wiring harness, the
"Engine Speed Switch" (the thing we are trying to figure out) and the TRC solenoid.

It even shows a picture of the switch mounted on the valve cover on page 214.

I'm sure this is the mystery box...

wow, - now check this out! - He is proved correct. GM actually mounted those relays on valvecovers.... sorry I really couldn`t imagine..

[JohnC]

El Gracho you are the MAN

[DirtyLarry]

I will start eating my shoe as well. I would have never guess GM would mount any relay on the valve cover. Someone pass the Tabasco souce please.....

[cjracing15]

Well I will be diped.

[Square84]

my buddy has a 85 1 ton with a 350/th400 and his has it but he has an edelbrock carb and if you unplug his the truck won't start?