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Zigzag03 · 01-12-2020, 08:02 AM

I am trying to assist a friend with a trailer lighting issue. I consider myself pretty good at electrical, having been in the auto/marine trade for more than 30 years. Kiss of death, no doubt!
The vehicle is a 98 Pontiac Transport. The trailer has a new incandescent light/wiring system, and the vehicle has a new plug and harness which goes to the LH taillight assembly.
When hooked to the vehicle, I have parking lights, but brake and turn are very dim, even with engine running. Hooked to a different vehicle, the trailer lights work fine.
While the alternator at the battery puts out 13.8 minimum, at idle, at the trailer plug I'm seeing 12.6 on the parking light wire, and only 11.5 on the brake light wires when pedal is pushed. I know there's a voltage drop from the two vehicle stop bulbs, but I don't understand why I don't get close to system voltage at the plug. 12.6 at the parking lights MIGHT be explained by the parking, side marker and plate bulbs, but even that seems low. It doesn't matter where I take the ground from, either the white wire at the plug or direct to vehicle chassis, and I get 0.00 ohms when testing between plug ground and chassis.
Besides possible poor connections at the tailight hookup, is it possible that there could be a flasher issue here, perhaps requiring something more heavy duty than stock? I'd be grateful to hear some opinions on this, as I'm heading over to inspect the taillight hook up (I didn't do it), and test voltages at the connection points later this afternoon. Many thanks.

kdauto · 01-12-2020, 08:16 AM

Has the 4 or 7 pin wiring simply been spliced in or was a converter box used?

If a converter box was used, was it one with a power wire running directly to the battery? Most newer vehicles require this as factory wiring gauge is too small to power additional lights.

Zigzag03 · 01-12-2020, 08:19 AM

This I do not know, on list for discovery later today. This is a 98, doesn't seem old to this old guy but probably no longer qualifies as "newer" vehicle!

Zigzag03 · 01-12-2020, 08:20 AM

4 pin, btw

Bipeflier · 01-12-2020, 10:09 AM

Run a seperate ground wire (12AWG) direct to the tow vehicle battery ground and see what you get.

Zigzag03 · 01-12-2020, 11:04 AM

Despite the 0.00 ohm ground reading, I found that the ground had been hooked up to a painted surface, and scraping this to bare metal restored full brightness to all lights. Still needs a converter, since the turn signals blink both sides at the same time, but the bigger mystery is solved. Thanks for response!

kdauto · 01-12-2020, 11:36 AM

Quote:

Originally Posted by Zigzag03

Despite the 0.00 ohm ground reading, I found that the ground had been hooked up to a painted surface, and scraping this to bare metal restored full brightness to all lights. Still needs a converter, since the turn signals blink both sides at the same time, but the bigger mystery is solved. Thanks for response!

Ohm testing is kinda useless as just a single strand of ground wire will yield 0 ohms. There is not enough surface area to move all the electrons needed to power up a bunch of lights so voltage drop testing is more acurate.

steve52 · 01-14-2020, 10:26 AM

Quote:

Originally Posted by kdauto

Ohm testing is kinda useless as just a single strand of ground wire will yield 0 ohms. There is not enough surface area to move all the electrons needed to power up a bunch of lights so voltage drop testing is more acurate.

Multimeter checks voltage. Test lamp verifies current is actually flowing.

kdauto · 01-14-2020, 11:17 AM

Quote:

Originally Posted by steve52

Multimeter checks voltage. Test lamp verifies current is actually flowing.

Yes, but you can use a voltage check on the ground wire to see if the ground is worth a darn or not conducting well enough. I use it at my shop almost every week to test stuff other shops miss.