Car Stereos: Deck doesnt hold memory, red hot wire, amp fuse

Question
Brian,
I've got a problem I've never encountered before. I just installed a Pioneer DEH-p3000IB cd deck in my 93 cougar,I purchased the wiring harness also.

After hooking everything up,I noticed I get no power in Acc mode...the only way I'm able to get the stereo to work,is if I also connect the 12v (yellow) to the red hot wire...so this makes the memory useless on this stereo.

I had to twist the red and yellow wires from the stereo together in order for it to work. I know this isn't right,I did check the red wire from the harness,and all was fine...but when I checked the yellow (from the harness) I got nothing,so I was wondering.....where would I find the constant (yellow) feed I need in order to keep all my settings in tact when I shut the car off?

Thanks for any help.

Answer
Hi Kevin,

There's definitely a constant power wire present in the factory radio plug, represented by the yellow wire in the adapter harness.  It should match up with a factory wire that's green with a yellow stripe.   

If the factory constant power wire doesn't have any voltage, the most likely explanation by far is a blown fuse in the factory fuse box.  As it happens, this is a fairly common problem in the 90's Cougar and Thunderbird, because of the way the factory system is designed.  You should be able to find the radio memory fuse in the fuse box located in your car's engine compartment.  The fuse you're looking for is rated at 5 amps.

If you re-wire the radio harness to the adapter wiring (yellow to yellow, red to red), then replace this fuse, your new CD player should start working correctly.  However, it's very likely that the fuse will blow again at some point, because a 5-amp fuse isn't large enough to supply your CD player.  That's the difference between the factory radio and your after-market system:  the original radio in the Cougar drew most of its operating power through the "accessory" connection, and the "memory" wire's function was just to keep the presets and clock memory stored.  However, an after-market deck uses the "accessory" connection as a turn-on signal, and draws almost all of its operating power through the "memory" lead.  That's why a 5-amp supply that's ample for the factory radio is undersized when an after-market deck is installed.

So what can you do about it?  Well, the obvious solution is to replace the 5-amp fuse with a 7.5 amp or 10-amp one.  This is what most people do, and it will probably work without a problem.  However, I hate to recommend increasing a factory fuse size, just as a matter of principle.

A better solution is to run a new constant power wire for your after-market deck, instead of using the under-sized factory circuit.  Possible voltage sources for the new wire are the battery, fuse box, ignition harness or cigarette lighter wiring.  If you run a new wire, it's a good idea to put a 10-amp fuse on the wire within a few inches of your voltage source.

I hope this helps!  Thanks for your question.

Brian