Homebuilders Expertise Appreciated on NAV 122d install

Since I figure you guys have installed or built just about every manner of flying conveyance and experimented with all forms of flying machine, I'm hoping someone out there can give me some guidance on this little problem with my far less exciting than experimental Grumman AA1. I had Narco 122 (original 1970's unit) give up the ghost on me so I purchased a newer Narco 122 d/gps unit to replace it (supposedly a pin for pin swap that doesn't require any additional wiring). I put the unit in the same location and used the legacy connector and antenna wires and was able to get the VOR Morse code signal to come through, however when I went flying this morning the GS and Nav needles didn't actually indicate anything! Any ideas? I will say that I failed to connect the ground lug in the back of the unit (will remedy that this weekend). Would my failure to attach the grounding wire have any impact on the unit's function or am I looking at checking in with an avionics shop? Any advice would be appreciated.

I put the same unit (122-d-GPS) to replace an older unit in my AA1B and it worked fine.
Yes you need to make ALL the connections including the ground!
Check and re-check that all your mating connectors are clean and bright. This includes the power, signal, ground and antenna connections. Also check the VOR antenna on the vertical stab too; a cracked insulator, loose wisker or a poor connection will cause you problems.
Out of curiousity; in what manner did your 122 fail? Also; don't throw it away, even dead it's worth good money in parts...

Chris

Hiper,

Thanks for the reply, I had the feeling that something simple may be causing the problem. As for how the old 122 kicked the bucket, I have to revert to what the previous owner(s) told me. Basically (and from my limited understanding) the unit was no longer indicating (I think the gears were stripped) so they bought a GPS 196 and stuck that on the windshield...the mechanic pulled the old unit out before I bought the plane and left a blank cover plate. I'm trying to get my IFR rating and figured it would be most cost effective (HAH!) if I replaced the 122 with another since it wouldn't require any modifications and since all the plugs and antennas were still there unlike say trying to plug a GNS 430 into the dash. I'll hook up that ground wire this weekend and check the quality of the BNC connectors hopefully that will fix it.

I hooked up that ground wire on Saturday but still no love. Looks like I'm heading to an avionics shop for someone else to take a look and see what they can find.

Hiperbipe is correct. The old radio does have value and I am interested, if you still have it ( I realize this is an old post).