Headlight module question

I'm converting the headlight motor control system on my '85 'Vette, with it's 3 external relays and 3 internal switches per motor to use a module from an '87 and up Firebird. I got the module from a salvage yard and after hooking everything up there was no ground output from the module. The + output was switching but no -. I figured the module had to be bad so I went back to the Pick-N-Pull and exchanged it for another one. Got it home and.....same thing :mad: It seems unlikely to get 2 in a row with the same problem but everything else seems to be good. The input ground is good at the harness pin. I can't think of what I'm missing. :screwy: Does anyone have a manual with a diagnostic procedure for the module? Is it possible to check/test one with a DVOM?
Thanks in advance for any help.

you picked the worst headlight system in the world to try and be fixing man.Mines an 82.At first it was that they messed up in the rain.Then after i bought all new relays and replaced one headlight motor just cause it was noisy now they dont work at all.The relays was 17 bucks apiece.The headlight motor was $50.00 used,and i tested it making sure it worked on the car i got it from ,using the new relays i bought to test it with.I know i should try and replace the headlight switch or make sure its plugged in,but after all that i just screwed them up manually,pulled the relays and forgot about it.Good luck

Anybody else? :banghead: