Maker Pro
Maker Pro

Question on relays

R

Raul Rivera

Jan 1, 1970
0
I want to install a relay that will light up my third brake light on my car
when a certain signal is generated by the ECU. The problem is, the brake
light circuit is also wired to the brake pedal and if I activate the light
with the ECU signal, won't the current also flow back throught the brake
wiring? Do I have to install diodes on both circuits so this won't happen?

Here are more specifics...

I have an -88 Honda CRX Si car with an engine swap. The new engine uses
Honda's VTEC technology. I put a VTEC sticker on my third brake light so
when the brakes are depressed, the VTEC sticker lights up.

VTEC is activated by the ECU at 6000 rpms and I want to use this signal via
a relay to light the VTEC sticker. My concern is that when that happens, the
current may pass back to the brake circuit. The same when I depress the
brakes - the current will flow back to the ECU.

HELP!
 
D

DaveC

Jan 1, 1970
0
VTEC is activated by the ECU at 6000 rpms and I want to use this signal via
a relay to light the VTEC sticker. My concern is that when that happens, the
current may pass back to the brake circuit. The same when I depress the
brakes - the current will flow back to the ECU.

Install 1 diode (100v silicon rectifier such as 1N4002) in each wire from the
brake switch and the ECU:

1n4002 1n4002
from brake switch --->|---+---|<--- from VTEC signal (ECU)
|
|
to 12v ^ |
| |
| 8
relay contacts \ 8 relay coil
| 8
| |
bulb @ |
| |
| |
+---+
|
===
GND

Good luck,
 
Top