'94 SL500 no start

[jcciem]

'94 SL500 used a couple times a week never a problem with starting until today. When I attempt a start, all warning lights in the instrument panel light up as expected. But when I turn to start the car nothing happens except a slow regular low beeping sound from somewhere in the dash or center column or instrument panel and at the same time the roll over protection bar switch flashes and the snowtire light switch is lit. It's not the battery because I substituted the battery from my other car and it still does the same thing. Things I've checked so far, removed every fuse in both the trunk and under the hood and cleaned the fuse tips and contact points. Disconnected the battery for a half hour then reconnected it. Locked and unlocked the doors with the key, and then the remote, found a relay with a fuse in it checked and cleaned the contacts. I'm at a loss. Any ideas out there?

'94 SL500 56,000
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'89 300TE 177,000