Weird Electrical Problem
Thread Starter
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Mountain Pass
Joined: May 2004
Posts: 201
Likes: 1
From: El Paso, TX
Weird Electrical Problem
Well, here it is. On my 89 f150 I6 the gauges move when ever the a/c is on. For example, with the a/c off the temp reads at the "n", the oil pressure reads at the "m" and the voltmeter in exactly half on the gauge. Turn the a/c on and the temp immediately jumps to the "o", the oil pressure goes past the "l" and the voltage drops below half. I suppose this is not very strange and should be expected; perhaps a bad voltage regulator? The strange part is what happens to the cruise control. If I have the a/c on and set the cruise, the engine and vehicle speed will increase every time I use the mic on my cb radio. Is it just me or is that strange? What do you guys think about these problems? Thanks for any advice.
Post Fiend
Joined: Oct 2003
Posts: 6,214
Likes: 13
From: New Jersey
This could indicate a few different things.
Odd gauge movement like that where all the gauges move up slightly, and the voltage gauge moves down, usually indicates a weak battery or a dying alternator/regulator.
Warm the truck up to operating temperature, then let it idle in park or neutral. Connect a voltmeter across the battery, and you should see a hair over 13V. Then when you click on the A/C (have a friend sit inside and do it for you, leaving the truck in park or neutral), and watch the volt meter.
It will likely dip for a split second to 11.5-12V then almost imediately jump back to whatever you saw while it was idling with the AC off.
If the voltage goes down, it might be that the A/C idle setting is off, or the alternator/regulator might be marginal and going to die fairly soon.
Also check on the passenger side of the engine if the grounding strap between the firewall and the engine is not rotted out completely. When that grounding strap goes, sometimes Fords of all kinds start to do weirdo things.
Odd gauge movement like that where all the gauges move up slightly, and the voltage gauge moves down, usually indicates a weak battery or a dying alternator/regulator.
Warm the truck up to operating temperature, then let it idle in park or neutral. Connect a voltmeter across the battery, and you should see a hair over 13V. Then when you click on the A/C (have a friend sit inside and do it for you, leaving the truck in park or neutral), and watch the volt meter.
It will likely dip for a split second to 11.5-12V then almost imediately jump back to whatever you saw while it was idling with the AC off.
If the voltage goes down, it might be that the A/C idle setting is off, or the alternator/regulator might be marginal and going to die fairly soon.
Also check on the passenger side of the engine if the grounding strap between the firewall and the engine is not rotted out completely. When that grounding strap goes, sometimes Fords of all kinds start to do weirdo things.
