What is the other relay for?
 

Does anyone know why some 87's have two relays on the firewall. I know one is for the fuel pump, but what is the other one for?
Thanks

Re: What is the other relay for?
 

If it has an M40 trans it's a downshift relay.

Re: What is the other relay for?
 

Thanks. I've be a chevy guy for a long time and had never heard of M40. Learn something new everyday.

Re: What is the other relay for?
 

M40 is the RPO code for the TH400 transmission.

Re: What is the other relay for?
 

I'm surprised to see a TH400 in a shortbed 1/2 ton. Seems overkill.

Re: What is the other relay for?
 

Yeah, I've seen a few 87 1/2 tons with a TH400 behind a 305. Definitely overkill, but I think TH350's had been phased out by 1987, leaving the TH400 as the only non-overdrive automatic available.

Re: What is the other relay for?
 

Late to this party, I know, but have a footnote for this topic someone might find of some use. I have a '87 shortbed 2wd with the 4.3 and a TH375 from the factory. Made the discovery when it came time to replace the output shaft seal. Prior to that was curious why the hd tranny was in such a light truck.
Planning to replace it with a manual 5 speed so if anyone needs one it will eventually be available at a really good deal (includes the relay!).