Correct voltages at hitch end

[Roundhead]

I've been tracing the wiring on my 1993 Suburban to convert its 6-pin plug to a modern 7-way RV plug before I tow my 1971 A/S.

I think I'm getting close.

However, to be sure, I'm verifying connections, voltage, resistance, etc., using a multimeter.

The charge line gives me a solid 12.0 DCV, and the brake line voltage varies at something under 12 volts. That seems AOK.

But signals and running lights are not giving me the full 12 volts when "hot". Lights are 10.x DCV and voltage of turn signals ramps up and down, never exceeding 4.0 DCV.

How am I doing here? Shouldn't each lead give me a 12-volt reading when "hot"?

Has anyone done similar testing? What results? Tips?

Thanks.

Roundhead

[uwe]

What kind of a meter are you using? Some meters have a slow response, so the turn signal interval might not allow a full reading.
You should get more than 12V at the charge line with the engine running. I get 13.4 V while running, and 12.6 with the engine off. My lights read 12.5V.
Do check your meter first - I own 4 of them and one of them is drastically off.( It's a digital one from Radio Shack)
Also, make sure that there is no corrosion where you put the ground connector, and that the terminals of the plug are corrosion free.
I am not sure what the brake wire should read - that one is not exactly the same on my vehicle as the lights, but yet the brakes work great.
I make it a habit to check all the ground connections first, that way you can be sure not to have grounding problems.
Good luck with your test.

[Roundhead]

Thx. Uwe.

I tested without the engine running....I'll try again with it running.

I think the ground is good. I found good continuity.

[Roundhead]

My digital multimeter is a Sperry DM 4400. (45 bucks at Home Depot).

[uwe]

That would be a good quality meter.
Some voltage drop is normal, it is a long run from the front of the truck all the way to the rear. It is really minimal, though on my Dodge 350 extended van.

[john hd]

roundhead,

i work for the power company, on my crew alone we have 5 voltmeters.

all of them cost over 250 bucks each, no two of them have the same reading. some are off by 5 to 10 volts!

check yours against another meter, and go from there.

what do you get right at your battery?

if you get good voltage there and bad or low voltage at the rear end, you need to look for bad connections.

you cold have good voltage at your plug and not know it because your meter is off.

john

[Roundhead]

I don't think its the gauge.

I re-tested it with the vehicle running, and the voltage on the charge terminal and running lights is OK. 13.4 and 12.8

I'll just keep working on the other lines till I find the problem.

Just wanted to be sure I wasn't trying to fix something (low voltage) that wasn't actually fine as is.