What are these relays on my firewall and do I need them?

[fender89]

Key on specifically, not starting. But if not, thats good. Also, i may not be 100% correct on this, but your drums are bigger, is your truck have C6p on the SPID label at all, the bigger rear brakes, in my mind, would see you have the next size up master cylinder(plus yours would have a plastic reservoir in 85 i think?) but i could be wrong. it matches my 78 k10s master/booster, but my 80 gmc has the master with 2 hold down wires and I also have larger rear brakes but htat is because I have c6p.

yes it does c6p - heavy duty chassis
also e60 heady duty front spr
it also shows mx1 options code for tranny. but i have identified it to have the th400. so maybe someone put in the 400, or mx1 does not specify 350 or 400

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[AuroraGirl]

yes it does c6p - heavy duty chassis
also e60 heady duty front spr
it also shows mx1 options code for tranny. but i have identified it to have the th400. so maybe someone put in the 400, or mx1 does not specify 350 or 400

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im pretty sure mx1 is th350. but i could be wrong. your year is also different than mine, so nvm, th350 were on the down swing then. does your shift indicator say PRNDL(2)L(1) or does it say PRNDSL or does it say PRNOD21 or something else?
if it has only 3 speeds on it, its almost assuredly th400 factory in my view
However this makes me think you have the wrong master

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this is a 70s but this is, im pretty sure, the size yours should be. the reservoir would be plastic however.

Well now im not so sure. those boosters are different size, right, the one on the older truck looks bigger. hmm

 

[fender89]

im pretty sure mx1 is th350. but i could be wrong. your year is also different than mine, so nvm, th350 were on the down swing then. does your shift indicator say PRNDL(2)L(1) or does it say PRNDSL or does it say PRNOD21 or something else?
if it has only 3 speeds on it, its almost assuredly th400 factory in my view
However this makes me think you have the wrong master

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this is a 70s but this is, im pretty sure, the size yours should be. the reservoir would be plastic however.

Well now im not so sure. those boosters are different size, right, the one on the older truck looks bigger. hmm

The shift indicator reads PRND21. It is a 3 speed automatic. Crawled underneath and the oil pan is clearly the 400..I was trying to figure out if it came with the 400 or someone put it in after that.
I'll have to look around for similar master cylinder. I'm not too familiar.

The truck was a fleet truck at a university.

 

[AuroraGirl]

The shift indicator reads PRND21. It is a 3 speed automatic. Crawled underneath and the oil pan is clearly the 400..I was trying to figure out if it came with the 400 or someone put it in after that.
I'll have to look around for similar master cylinder. I'm not too familiar.

The truck was a fleet truck at a university.

Hmm. but th400 sounds right for a HD c20 in the mid 80s. youre good

 

[JustaKid]

The box on the right is an emissions override relay. From what I can tell the plugs read (from left to right) power (wire color is pinkish with a black stripe), ground (black, grounded at the bell housing), Distributor (yellowish, RPM), fuse box (brown, leads inside cab), and I’m unsure of the last one as it has been cut by one of the POs.

I’m also currently trying to figure out either a delete or rewriting for this box. If anyone has any more information, I’d love to hear it as well.