I recently purchased a 1991 crx si and the rear defroster worked intermittently but now doesn't work at all. The fuse is good and I have 12 volts at the fuse itself, but the switch will not energize (no yellow light) I have good wiring to the rear of the car, but haven't purchased a repair manual yet. Any suggestions as to what part might have failed and how to test them? I'm leaning towards the switch itself, but don't want to buy a part unless I figure out how to test it first and if there is a relay in there somewhere I wanted to at least tap on it before switching it out. Any suggestions are appreciated. Thanks Jere

 

As with most newbies, I should have taken more time in the archives. After searching for about an hour, I found a fantastic reply to a post on troubleshooting the rear defroster issue by HondaHeddie. Since I knew my wiring was good I concentrated on the switch troubleshooting steps and narrowed it down to that piece. I'm going to use a removable jumper until my new one arrives, but I'm posting the steps below for everyone else to use. Thanks HondHeddie, that's good stuff!!
Jere

1. Check for voltage between drvr side window terminal(should be the pos term) and gnd(body)
if no voltage - faulty relay(in dash fusebox)-open wire

2.If there is voltage check for continuity from neg term(pass side) to body If no continuity bad gnd wire

3.If there is voltage at the pos term then you should read 6v from middle of each defgr window trace to neg term

To eliminate switch as issueThis is what I used)

open instrmt panel and unplug defog switch
turn ign ON
check for voltage between blak/yellow and blak wire
-if no voltage , broken blak/yellow wire

If there is voltage

connect a jumper from blak/yellow to blak/green terminals and turn on ign
deffoger should work with jumper
If it does the you have a bad switch

relay test:

Bottom of relay.
__----------------__
|...A.............C......|
|..........................|
|...B.............D......|
|_____________|

a-b should have continuity when bat is connected to c-d
a-b should be open when no bat