Low voltage ??

Ihave a 88 4x4 & need help tp find out why there is low voltage to the fuel pump, there is only 7.5 volts at the fire wall , can this be a bad key lock ??? Ihave change every think on this truck & still not running right !!!
thanks for the help .

I am not sure you should have much more than that with the engine running. Some cars only get the full 12 volts at the initial key on 3 seconds to prime the system, and then the volts drop off to around 7 or so.

Hope someone can verify that or help you.

I am not sure you should have much more than that with the engine running. Some cars only get the full 12 volts at the initial key on 3 seconds to prime the system, and then the volts drop off to around 7 or so.

Hope someone can verify that or help you.

Are you living in the 50"s when there were 6 volt positive ground systems?

Today's system voltages should be above battery voltage with truck running at 13-14.5 volts......

As for original poster- check for a bad frame rail ground at fuel pump-- being that old, corrosion will eat you up..

Thanks but so far no one knows what is wrong at all, the grounds are all good, new comp,dist,fuel pump,truck is a cherry , one of the first 88 built, that is why we keep it nice...But we need a full 12 + volts to the fuel pump for ti to run right !! This has the edelbrock injection & a custom chip, but just can not get the voltage to the pump !!! I Have the fire wall plug harness out in the cab & can test all the wires , but still can not get the voltage ?? This is why I was asking about the key switch ??? If I have to I will replace the steering column ??? or switch, there must be some on that has run into this a some time !!!!!
SHOULD I OFFER A REWARD !!!

Ignition key switch would not enter into your problem, since fuel pump runs through a relay.

Check every point from battery up to relay, then after relay, then in front of fuel pump connector- see where voltage drops off- then there is your issue.

Do you have a good wiring diagram?

Are you living in the 50"s when there were 6 volt positive ground systems?

Today's system voltages should be above battery voltage with truck running at 13-14.5 volts......

As for original poster- check for a bad frame rail ground at fuel pump-- being that old, corrosion will eat you up..

That's why I said not sure to begin the sentence. 50's is 25 years before my time. I was thinking ground to or pinched wire, but it sounds like his problem is in front of all that.

It's beyond my knowhow at this point, but I hope you get it figured out.

Ihave a 88 4x4 & need help tp find out why there is low voltage to the fuel pump, there is only 7.5 volts at the fire wall , can this be a bad key lock ??? Ihave change every think on this truck & still not running right !!!
thanks for the help .

with the meter negative lead secured to the battery ground probe from fuel pump fuse to the fuel pump. find where the voltage drops.

you should have a wiring diagram. 1988 is old stuff. with the wiring diagram this is no big deal.

the ignition switch being bad is possible.. that would show as low voltage to the fuses....if all fuses have the full 12 volts or 13-15volts with engine running it would not be the switch..

could be fuseable link is corroded..that could be at the starter ???

Thanks guys..
I have the fire wall plug out & it is on the inside if the cab along with all the other plugs from the turn sig + OK I lit up the main hot wire to the steering column, then check the wire coming from from wall plug to the fuel pump, & there is only 7.5 volts, + one plug to the steering column has the same voltage... Now I TURN OFF THE KEY & IT SHUTS OFF ALL THE VOLTAGE LIKE IT SHOULD !! Turn on the key & low voltages is still there.

I have all the manuals from that year truck, got them when we bought the truck ..There is a green wire at the fire wall & a pink one at the small plug the goes to the steering column..

There must be a wire shorted in the wire harness some place inside the cab ??
Will keep trying & let you all know when I find the trouble MUST BE ONE IN A MIL ??

Thanks guys..
I have the fire wall plug out & it is on the inside if the cab along with all the other plugs from the turn sig + OK I lit up the main hot wire to the steering column, then check the wire coming from from wall plug to the fuel pump, & there is only 7.5 volts, + one plug to the steering column has the same voltage... Now I TURN OFF THE KEY & IT SHUTS OFF ALL THE VOLTAGE LIKE IT SHOULD !! Turn on the key & low voltages is still there.

I have all the manuals from that year truck, got them when we bought the truck ..There is a green wire at the fire wall & a pink one at the small plug the goes to the steering column..

There must be a wire shorted in the wire harness some place inside the cab ??
Will keep trying & let you all know when I find the trouble MUST BE ONE IN A MIL ??

these type of problems are quite common with any vehicle this old. the wiring gets damaged and the more work done to the vehicle by auto mechanics the more problems with the electrical.

If the body shop workers ever did any work you can find a really bad condition .....they are the worst...

you start at the battery work toward the ignition switch feed. then to the switched ignition switch power out. and so on until you find the OPEN circuit which in one case for me was a OEM slice that corroded and caused my ac to work very poorly..vehicle was 14 yrs old..perfect condition original owner..this was in the sterring collum dash area in the wire harness all taped up....not an easy find...

these type of problems are quite common with any vehicle this old. the wiring gets damaged and the more work done to the vehicle by auto mechanics the more problems with the electrical.

If the body shop workers ever did any work you can find a really bad condition .....they are the worst...

you start at the battery work toward the ignition switch feed. then to the switched ignition switch power out. and so on until you find the OPEN circuit which in one case for me was a OEM slice that corroded and caused my ac to work very poorly..vehicle was 14 yrs old..perfect condition original owner..this was in the sterring collum dash area in the wire harness all taped up....not an easy find...

Thanks guys , Getting close to that bad wire !!