Wiring an aftermarket stereo in 1978 F-150 (can't get ground from battery)
 

I have a 1978 Ranger F150.

I am trying to wire a new Alpine CDE-SXM145BT head unit.

When I bought the truck, an aftermarket tape deck head unit had already been installed. I am now replacing that unit.

I used the last owner's original wiring job, but found very quickly that my newer model head unit would not retain programmed stations, Bluetooth devices, etc.

Here is the previous owner's configuration that I tried originally:This worked. Powered on, everything working. But nothing programmed gets retained in memory.

So, I ran a new 10guage wire directly off the battery. Wire comes from the battery, through a 20A in-line fuse, through the firewall, up the dash and to the head unit.

I replaced the original owner's battery (continuous) connection with my new wire.

No luck. The unit does not power on.

I got out my multimeter and checked DC current. Grounded to the battery post, it's running 12V. I checked at the connection at the battery, before the fuse, and after the fuse. All 12V.

Grounded to the ground screw in the cab, that same wire has no current.

Should I run a ground all the way back to the battery? I know the ground wire should be very short in length, and I know it is not a great idea to have a ground wire running that entire length.

Any ideas???

:-huh:-huh

Three options:
a) Test the ground wire itself - easiest way is to clip your test light ground to it and try a known good 12V like the center post of your cigarette lighter.
b) Test that continuous wire - if it is switched, you will lose your memory when you turn the ignition off. Normally on these units the switched power turns the unit off and on, and the continuous current is to power memory, clock, etc. functions.
c) The unit head may be defective. This is the least likely but still possible.

+1 on above. I'll bet you a nickel your constant 12v source is switched not constant. This sounds like it has nothing to do with your ground.

Well I hate to divulge my true n00bness, but the solution was simple:

I had the new continuous wire running from the negative battery post and not the positive post. :-X15

The wire from the negative post had a pigtail that I just jumped into, assuming I was on the right side of the battery.

So, I bought an insulated ring terminal, moved to the positive post, and all is working as expected - including the programmed stations, clock, etc.

Thx to all that looked & especially to those that offered advice! :-drink

Just an FYI....Back in the day there were head units with no ground wire... instead it was supposed to be grounded through the case and assumed the ground was provided by the factory metal bracket/hardware.

+1 to HIO Silver's comment - I have fixed intermittent weirdness in units before by adding a ground strap from a poorly grounded bracket to a good ground. The antenna wire won't cut it.


Jinxit - Guess that "continuous" wire was continuous... just not to a power source. You could always try building the world's first positive ground dentside!