What Is This? (Engine bay, 1970 C10.)
 

Me and my father are working on a 70 C10 currently and are nowhere near wiring pros, we learn as we go. But this has us stumped.

It's right on the firewall (square looking thing with prongs). We believe the engine is an early-mid 80s model (alternator on other side, choke on other sode, ect).

This truck has factory AC, and factory power steering. (If that helps)

Thanks in advance. Hope you guys can help.

BTW: pic is sideways, flip clockwise to have actual in person view. (New to posting pics)

Re: What Is This? (Engine bay, 1970 C10.)
 

Can you take a clearer pic using a flash? Its hard to see what we're lookin for.

Re: What Is This? (Engine bay, 1970 C10.)
 

No problem.

Re: What Is This? (Engine bay, 1970 C10.)
 

At first I thought it was a relay for the TCS system ( transmission controlled spark) but that didn't start until 1971 I believe. It also looks like the AC fan relay. Does the AC work in the truck?

Re: What Is This? (Engine bay, 1970 C10.)
 

It only works when I push all of the switches to the right. With me and my fathers limited knowledge, we believe the AC compressor is not there.

Re: What Is This? (Engine bay, 1970 C10.)
 

High speed windshield pressure sensor relay.?



(sorry that's all I got)

Re: What Is This? (Engine bay, 1970 C10.)
 

It appears to be a horn relay....not 100% sure but that is what it looks like. It has been added to that (non-original) position under the hood for some reason.
Check up under your dash above your main fuse panel to see if the original one is still there.
Does your horn work?
Coley

Re: What Is This? (Engine bay, 1970 C10.)
 

I had one there on my 71 it wasnt hooked up and wasint in the new harness if i went with out it

Re: What Is This? (Engine bay, 1970 C10.)
 

My 1970 Blazer has this. It has no A/C, possibly relay for high idle solenoid?

Re: What Is This? (Engine bay, 1970 C10.)
 

Came across this old thread while looking at wiring pictures. I have that thing on my firewall too. And it had me stumped too According to the 1970 factory service manual, it's the relay for the transmission controlled spark system. Mine actually had wires attached and running down to the trans area, although it wasn't plugged in. My truck has factory air too and I had thought it might be something for it, but the manual is pretty clear. Cheers!