unplug the pump and see what the voltages are (or was that measurement made with the pump unplugged) -- a shorted pump would show values like that and the Balast usually will keep the fuse from blowing (with the balast in the circuit there's only like 11 amps being pulled by a shorted pump).
You didn't mention any voltage measurements at the balast resistor - take those under bothe sets of conditions -- the pump side of the balast should "roughly" correlate with the info you collected at the pump plug and the other side of the balast should show 12V with key-on...
The thinking is that if the plug shows data which does not correlate with the plug - then you've developed resistance or damage in the harness between those two-points, if the pump side of the balast shows what you're seeing at the pump and the other side of the balast is not exhibiting battery voltage, then the issue is supply side from there (relay/socket/fuse etc...)
When you find that the supply at the ballast is inadequate, pull the fuel-Pump relay (the 2nd on from the front - the front one is the o2 heater relay) and probe it's contacts -- I believe that pin 5 is where the fuseable link connects (verify this the ballast wasn't in the original '87 design, so some of the installations were retrofitted to include the necessary, if pin 5 isn't hot key-off relay out, then pin 3 should be - you'll get the idea -- if 5 is hot then 3 represents the output of that relay to the balast.. or numbers are swapped) - Verify teh connections for the fuseable link and it's integrity - you can load the circuit (jumper from 5 to 3 - and measure there -- jumper will pass the pump current - could get a little warm be careful.
For reference (something not often posted) I've added the pin-out and socket diagram for the relays used on the MJ/XJs
RELAY PIN-OUTS
Code:
Euro Std Jeep Socket -- function
(Bosch) number
________ _______ ______________
-30- 1 Common
-85- 2 Coil (usually the ground)
-86- 5 Coil (usually the V+)
-87- 4 Normally Open
-87A- 3 Normally Closed
Looking at the SOCKET (relay removed) kinda is like this
Code:
|
|1
| |
2| ____ |5
3
____
4