ABS problem

We use a mastertech. Not only pulls codes, but can monitor the data stream and run function test and more.

The abs system is separate from the hydrolic brake system. I expect that you have a wheel speed sensor going bad. May be part of the wheel bearing and hub assy. Take a look for the wiring harnesses going to the sensors and check for damage or bad connections first.

You will need to pull codes from the body control module to narrow it down as you know.

Get an obdII scanner for your truck, it will pull the abs code from the datalink connector under your dash, the abs module works thru that link. Not only that, it'll work for all your obd needs, everyone should have one, not a whole bunch of money, depending on how complex you want to get. Most people probably spend more in a week on coffee and doughnuts

When my 1993 Explorer ABS light went on. I took it to the dealer and they told me it was either a sensor or the ABS relay. It wound up being a bad ABS relay. It is under the hood in the relay/fuse box and cost about $5.
Good luck.

That's a rarity! At least from what I have seen. But good to post none the less!

I don't know how much of a rarity. I have had to replace 2 of these in my car. The ABS relay and the electronic engine control relays. I even replaced one in my wife's car (maybe more of a precaution) when she said that her car stopped on her once.

Could this be a precursor to a bigger problem with my electrical system? What voltage should there be at the fuse block?

I really wish I could discuss electical testing intelligently and such, but I am still learning it. Therefore I can't answer the question of voltage. I just haven't seen many relays go bad versus sensors. It is certainly possible and on a larger may be more common.

My suggestion to to pull the codes from the computer, that should/could be of great help.
Tauruswheel suggested that earlier and is good advice.

I'm not sure how your scanner is set up, but the ABS codes will be in the body control module.

For the po174, Chris wrote a good post for that:
https://www.2carpros.com/forum/p0171p0174-ford-40l-common-causes-testing-and-fixes-vt27348.html

The Chilton repair manual (mine is the 26688 book, page 9-28) lists the codes for the 4WABS module. It states that "a scan tool such as Rotunda NGS tester 007-00500, is required to retrieve the codes."
It also has some replacement procedures for the ABS sensors and control units.
I don't see that info in the "Haynes" manual.