Brake light fuse blows, steps to diagnose?

[river251]

My brake light fuse in my 88 F150 blows right away. I have trailer light connector installed by Uhaul years ago.
I'm comfortable with a multimeter.

How do I search for the problem?

Thanks.

[way2old]

First you need to isolate the brake system on the truck. Place ground lead on trailer connector ground and place the power lead on the brake/turn signal pins on the trailer connector. Should be the yellow wire and a green wire. If either has continuity to ground, replace the trailer connector. If the connector proves out, do the same on the truck brake lights. You will find that one of them probably has continuity to ground.

[crank.it]

hi guys-88 is on the older side check out the wires that run under the carpet and sill plate they are often the culprit....crankit