What is this other relay plug for?

[Cartronics]

I have a 1989 GMC V3500 with no harness or plug for this empty relay spot and a 1989 Chevy V3500 with the harness and plug for this missing relay.
What is the missing relay for and why is the plug only on my Chevy?
It's on the driver side inner fender.

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[Old77]

I have the same setup as your first pic on my 91 R3500. Just assumed there was an option that my truck didn't come equipped with that others could have I'm intrigued to hear what others that know something may have to say

 

[ajd89]

Ive only one got 1 also. 89 crew cab

 

[RetroC10Sport]

What trans do you have?

 

[Cartronics]

turbo 400

 

[chengny]

I could only find 3 relays that were mounted on those clips - if the the truck came equipped with the associated option:

1. Auxiliary cooling fan relay

2. Daytime running lamp relay

3. Cold advance glow plug inhibit relay

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Since none of you guys are from Canada or are diesel powered, I would guess the relay you see is for an auxiliary cooling fan.

 

[gmachinz]

I’d bet if you have the tow package option RPO you got the HD cooling and aux fan which would use that relay spot.

 

[rpcraft]

Train horn relay!!

 

[Cartronics]

Yes, that's where I'll put the train horn relay. Yes, my neighbors will love me.