Where to tie in HEI? - Page 3 - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #31 of 35 (permalink) Old May 16th, 18, 9:45 PM
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Re: Where to tie in HEI?

Originally Posted by Dave Ray View Post
So, it seems that EVERY vehicle in the world that ever existed, and still do, need to be brought back in and have a billion dubious relays installed, by "professionals" to everything from ignition systems ti wireless headphones.

PLEASE, I do ignition systems for a living, see more than a LOT of basically well meant wrong stuff done, like relaying up a car for NO reason, and fix it when it fails, which is way past too often.

Of course, all you folks are all professionals, in automotive electrical systems and especially ignition systems, just why haven't you all convinced all the manufacturers to add every relay they possibly can to an ignition system, and fuses, and diodes, all sorts of electronics that really haven't needed to be there, FOR THE LAST 100 PLUS YEARS?
Nah I'll just keep quiet...

You're just jealous because you can't hear the voices!

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post #32 of 35 (permalink) Old May 17th, 18, 3:48 PM
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Re: Where to tie in HEI?

Originally Posted by oldcutlass View Post
Nah I'll just keep quiet...
Probably a good plan to keep from getting blasted.


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post #33 of 35 (permalink) Old May 19th, 18, 9:37 PM
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Re: Where to tie in HEI?

Golly, I'm surprised we didn't have some of the others chime in.....hmm....

Originally Posted by pnugene View Post
First thing comes to mind is computer outputs on modern cars are low current (and typically are switching the negative wiring on & off). Many of these relays have constant 12 volts on them and the CPU controls the negative side of the relay coils. The relay provides a means to use the low current output to control larger loads.


There ya go.

With more and more complex demands required from engineering to meet Federal safety, emissions, fuel usage etc. as well as increasingly complex creature comforts, modern vehicles must absolutely use microprocessor based modules to carry out all the functions efficiently and effectively. Even before the OBD systems coming into play, there was no turning back. There is literally nothing one can do in a modern car that doesn't involve a "request" through a module or digital serial communications between one or more modules.

With a few exceptions, most control modules have only low current capabilities. Either an open collector or open drain output to sink current. Relays are triggered by these outputs to carry out the final stage of the action. They do the "heavy lifting". The small current drawn from the relay coils are easily supplied by the control circuitry. Relays are cheaply and easily mass produced, even for special high current demands. Relays are a key and vital piece to the modern systems. It would be way too costly for vendors to supply several control modules that had the ability to switch many amps of current.

The days of a large B+ feed coming into the car and getting tied into a headlamp switch or HVAC control panel are long gone. No more switches or levers that trip a switch to send current to a device directly. Now when the driver or passenger activates something, they are merely sending a "request" to either something like a body control module, HVAC control module or infotainment module. Programmed instructions take a look at this request and then either allow or deny this based on multiple other inputs and active or stored conditions. If all acceptable conditions are met, then the action is carried out by activating a relay or relays.

The plus side of all this complexity as mentioned by Lucifershammer and Jwagner is greater weight and space savings. Heavier wiring can now be localized to the larger current carrying device area. Smaller more stylish switches can be used as they only supply small signal currents. Instead of multiple, varying gauge conductors being spread across the car, now small data lines can be run from module to module and the modules make the decisions for their area of specialty with only enough needed wiring to get the job done.

There ya go.

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post #34 of 35 (permalink) Old May 20th, 18, 12:38 PM
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Re: Where to tie in HEI?

Come on over, you can go through all the busted relays you care to, take 'em home, enjoy them, play with them to your heart's content, they were DOA when they got here in people's cars. 95 or so percent of them were put in to "fix" a circuit that was done incorrectly in the first place, NOT OEM installed. I have a nice 1991 Toyota Camry daily driver, just turned 150K miles, it has all sorts of JAPANESE made electronics, including factory placed relays, never a problem. The ones I have removed are all after-market ones, NOT OEM, used in some very stupid, idiotic places they never should have been placed.

Too bad if some of you can't take the real truth about things you are misled into blindly believing. A relay in a correctly designed circuit that didn't have, and/or, need one in the first place, is a crutch, NOT a real fix.

Live with it.
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post #35 of 35 (permalink) Old May 21st, 18, 5:58 AM
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Re: Where to tie in HEI?


It is not us that have a problem with 'the real truth' as you put it.

If I read you correctly, you have just stated that relay problems are caused by idiots not using them correctly, or words similar. How is that the relay's fault?? If you smack your finger with the hammer, is it the hammer's fault?

The facts are that relays are incredibly reliable & the numbers speak for themselves. That assumes they have been wired up correctly, & the relay is rated to do the job.
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