relays for electric fan in truck

x2! Looks good. A nice solution. And now even using conventional 85 & 86 polarity (relay coil). Definitely worth the transient suppression diode across fan relay 86-85 unless the ECU output is a relay (but it's probably an Open-Collector transistor/FET output). And #85 to ECU diode as suggested - just in case!

What kind of diodes would I need and can I get them at Radio shack?

1N4004, yes to Radio Shack, the band sides of the diodes go to 86 (pos. coil) and the other sides to 85 (neg. coil).

Thanks.

How would I add a diode to the engine computer trigger line to keep ground from being applied to it when it isn't activated but the A/C trigger line is?

I see that those diodes are rated at 1 amp...that doesn't seem like very much ?

kaztheminotaur wrote: I realize that is more relay than i will need but better to over build it than under build it...

Not when its 2/3A solenoid blows the ECU. And not when it's big, clunky, overpriced, a fitting issue (ie hazard), etc. Normal 30A or 15A relays will do fine, with nice spade connectors for easy replacement.

Well answered Pete. 1 amp diodes are more than adequate for the coil draw on NORMAL relays, also use 4 pin where you can, the current ratings are higher. Your other question, the answer is in line on the ground switch to terminal 85, band away from the relay.

oldspark wrote: kaztheminotaur wrote: I realize that is more relay than i will need but better to over build it than under build it... Not when its 2/3A solenoid blows the ECU. And not when it's big, clunky, overpriced, a fitting issue (ie hazard), etc. Normal 30A or 15A relays will do fine, with nice spade connectors for easy replacement.

I don't follow you on the 2/3 A solenoid blows the ECU ?

Thanks you Howie. Unfortunately however, I regret to inform you that YOU are WRONG! (Bear with me readers, this is for fun - Howie is right, but shhh!) As per some other "expert advice" forum (alas I do not know which), I hereby present the following: (Howie - skip this line. Others - DO NOT follow the next advice - instead follow Howie's above!! DO NOT FOLLOW THE ADVICE IN THE ABOVE IMAGE I originally included something like the above in my last reply, but later deleted it after I thought I got it wrong! But I am right... amn't I...   [For quenching - Kathode/line towards +ve (#86); anode to gnd/negative (#85)] ? ....or &? I think I'm right - never trust expert forums. Except this one. And Howie. BTW - I was thinking the 1A diode was enough for the quenching. [And yes, it should be 400V; 200V can be a bit low. Besides, the IN4004 400V/1A is now generally "the common" lowest rated diode - ie, lesser rated power diodes cost more!] But it is also fine in series with any "normal" relay - even the oversized 100A relay with its 8W = ~0.7A solenoid/coil. I'm even thinking of buying a bulk pack of 1N4004 (a few dollar$ for 100) and throwing out those unlabelled 50V 1A I got years ago for 2c each - 50V "unpolarised" cleanskins just ain't worth it!) Rem: Hail Howie!!