I have recently purchased a 1979 Mercury Cougar XR7. Interested plan on restoring it. It is in Fair condition. So far I have had the carburetor rebuilt and a new starter put in. I, myself, have replaced the alternator, the coil, the fuel pump, the starter solenoid, the voltage regulator, and the positive battery terminal wire. My battery is also brand new. Now, recently I have been having some issues. It seems that either the battery drains over night, or form the fuse that runs the ignition, dome light, and key buzzer is bad. I say thus because I will get it running and then suddenly it wont start. I get no sound from the starter at all. And also the dome light wont come on and the key buzzer wont work. Does anyone have a clue what it could be?
Here’s my standard instructions for finding electrical shorts and/or excessive current draws:
First, always install electrical wiring with the battery disconnected.
Physically install the underdash harness with fuses. Connect all underhood and taillight harnesses.
When ready to check out the harness, close all doors, turn off all lights, ignition key in the OFF position, accessories off, etc. Make sure both battery connectors are disconnected. Connect the positive battery cable to the starter solenoid. Leave the negative terminal disconnected from the battery. Then use a digital volt meter to measure the current draw across the battery. Place one probe of the DVM on the negative battery cable terminal, and the other probe on the negative battery post. Be sure that the DVM is set to amps, DC. If there are no shorts in the wiring connections, the reading should be on the order of 30 milliamps or less. Anything above 1 amp indicates some accessory is on; readings above 10 amps (may blow the fuse on the DVM) indicates a dead short.
If you have a short, disconnect all other wiring from the starter solenoid post where the battery connects and re-measure the current. If current drops, the source is the underdash wiring harness or the harness from the starter solenoid to the firewall. Reconnect the wiring to the starter post and then disconnect the underhood harness from the firewall and test again to isolate the source of the short.
If the short is not in the underhood or underdash harness, the problem lies in the alternator or voltage regulator. Disconnect each of these in turn to isolate the source.
If the short or high current comes from the underdash region, keep the battery negative side disconnected and remove one fuse at a time. Measure the current as above. If you now see low current, there is either a short or an item on that particular fuse circuit is on. Turn off that item and continue checking.
Eventually, you’ll have low current readings with all fuses installed and all wiring connected. This series of tests checks all of the battery directly powered systems. To check the Accessory systems, now repeat all of the tests above with the ignition key in the ACC position. The current with the key in the ACC position may be up to 1 amp or so. When all of the tests are done and no anomalous current is noted, at that time, and only at that time, is it safe to connect the negative battery cable to the battery.
That is completely confusing. First because if nothing is connected to th positive post on the battery itself then there is no current at all. Second, Im not installung the new harness, just trying to find out what is draning the battery.
Although the advice was written for installing new harnesses, the steps to find shorts are straightforward. As I said, you start with both terminals disconnected, but then connect only the positive side. You use the negative side to measure current. By the process of elimination of which fuse or if no fuses reduces current flow, then removal of various lines attached to the starter solenoid should isolate what circuit is draining your battery.
These instructions have been provided to my customers for 8+ years without a single issue in not finding the problem.
Tony based on it going from running fine to suddenly not starting and acting completely dead, I’d be inclined to think it’s something faulty in the ignition or a bad solenoid. The advice midlife is giving you is correct and exactly what you will probably need to do. I hate electrical and usually get a hand from someone to track down gremlins like that.
I used a multimeter. Charged the battery. Fully charged it read 12.30. I connected only the positive terminal. All doors were clised, lights off, radio disconnected, etc. Then I bridged the negative post with the negative wire. It read 12.30. Which means that something is drawing all 12.30 volts while my car is parked.
And I already replaced the alternator, the battery, and the solenoid.
Tony I think you are still just measuring the battery voltage. what you want to do is hook up the multimeter between the negative battery post and the negative cable. (if I’m ready midlife’s post correct). remember to set it to DC amps.
Yes, the voltage between the negative disconnected battery connector and the negative battery post will read battery voltage. You want to measure DC current. Be sure that your multimeter leads are properly located, as most units require the positive lead to be in a different position than voltage or resistance readings.
Any progress? Let us know how it goes.
I tried a voltage meter. It was a cheapo one that didnt have the right settings. So i triedvthe testblight method. With tbe doors closed and everything possible disconnected, i disconnected the ground wire from the terminal on the battery and bridged them with a test light. It came on indicating a current draw on my battery. So i fixed the test light in place and began pulling the fuses one by one until the light turned off. That didnt work. I know on some older cars, power seats and power windows arent run through the fuse box. Does anyone know if this is the case with the 79 XR7?
This is a 1979 and not a 1969? It doesn’t matter…the test procedures should still work.
Did you disconnect everything on the battery side of the starter solenoid except for the battery and alternator? That’s the next step. Did you disconnect the voltage regulator plug? Final step is to disconnect the alternator from the starter solenoid. At this point, you only have the battery connected to the starter solenoid and nothing else. Remove all other wires at the starter solenoid and see if you are still drawing current. If so, it has to be the starter solenoid by a process of elimination.
I diconnected the starter wire from the solenoid. My alternator has a positive post, a ground post, and a plug. The positive wire and plug run directly to the voltage regulator. I found out, through process of elimination by disconnecting and reconnecting everything from my solenoid, that the draw only occurs when the plug is in the alternator and the wire that leads to the distributor is connected to the solenoid. Individually connected, there is no draw. But when both are connected there is a draw. Being that the only thing connected that would draw power was the alternator, I am assuming thats what is causing the draw. And because the alternator still puts out a charge, I am assuming the cause of the draw is a bad diode.
Fuse pull test showed NOTHING. Replaced the alternator… AGAIN!!! Still a draw on my battery!!! I am about ready to put a canon fuse in the gas tank and applaud when it explodes. Any help would be appreciated…
What wire leads to the distributor that is connected to the solenoid? Are you talking about the 90* slip-on connector further away from the battery post on the starter solenoid? If not, there’s something attached that shouldn’t be there unless you have an aftermarket ignition system. That 90* connector That should not draw power unless the starter solenoid is engaged or the ignition switch is in the RUN position. Have you disconnected your ignition switch?
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