What does the main relay do ?

Asked by Nov 18, 2015 at 02:55 PM about the Mercury Grand Marquis

Question type: Maintenance & Repair

when I put the key in the ignition, and go to start, all warning lights come on and then I hear a click and lose all power, just like a dead battery, then I disconnect the battery and reconnect all power come back, until I again try to start the car, then when I again turn the key in the key in the ignition, and go to start, all warning lights come on and then I hear a click and lose all power, just like a dead battery, then I disconnect the battery and reconnect all power come back, then repeat, until car finally starts & runs normally.

2 Answers

57,155

Clean your battery terminals and the cable ends. I think you have a bad battery connection. If you cannot tighten up the connections properly then you may need new battery cables.

Well, Thank you for your effort. I do believe to start simple & work into the details of the system. Being the electrical system, this would be one of the few simple starting points. I started with the ignition switch, which had one burnt contact causing it not start 1 out of 5 times, unless you open and closed the door (vibration caused the lose connection to let it start). However, I took your suggestion knowing I have clean contacts, a 2 year old good 1200amp special service battery and had moved the relays around. WHAT I DID NOT NOTICE BEFORE IS THAT THE ORIGINALCABLE THOUGH IN GOOD ORDER & CLEAN, THAT THE POS CABLE SPLITS OFF INTO TWO SMALLER WIRES, BOTH CONNECTED TO THE MAIN RELAY BOX... WHEN I MOVE THE TWO SMALLER CABLES PRIOR TO STARTING, THE CAR STARTED 10 TIMES IN A ROW, AND WITH THE ALL LIGHTS & ACCESSORIES ON THIS TIME. THANK YOU, with your simple suggestion, I went back through & found what seems to be a week link that I will replace with a new POS CABLE (less than a 1foot cable). Thank you again,

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