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1lo620

620 lost power at key.

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So it started out with loosing the ability to turn truck over with key. But have been jumping it with hand held trigger. But now I lost my low beams on headlights driving home the other day. Now I have no dash warning lights and my lights won't come on at all. Battery is fine it will turn over with the trigger starter. But won't start.. I am not an electronic guy and just a moderate mechanic. Where should I look start...???

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Which 620? '77 or '74.

 

 

If the truck runs then not the fusible link. Also not the power to the ignition switch.

 

 

LIGHTS

If 4 way flasher works then you have power to the fuse for the lights. Hold a quarter across the fuse terminals of the 10 amp fuse closest to you on the left side of the fuse box. This is for either truck. Lights should come on. Fuse is blown or bad contact. Clean clips an/or replace fuse. 

 

 

STARTER

Check that the small Black/Yellow wire to the starter solenoid is secure and tight on the solenoid. If OK pull wire off and check voltage to it when in the START position. If near 12v and no start then the solenoid may be bad. If 4-8V then the start signal is weak.  Use this weak signal to trip a hot start relay....  

 

 

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It doesn't run I can turn the starter over with the bypass trigger. But the truck won't start now. I have no lights no turn signals no dash warning lights. It is just like everything just turned off. It is on my 74. All fuses in block are fine. Hate electronics..

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My guess is a bad positive battery cable...maybe it has the greenish oxidization inside like my "79 Kinkcab had which gave mine similar symptoms.....

 

Vicdat

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If the starter can turn the engine over then not the battery posts. Starters draw hundreds of amps.

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Why not start where it is failing....

Get a test light and see if power is passing through the switch .... 

 

Could be as simple as the ignition switch failed.....

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wiggle the key switch connector in back.

 

pull the START WIRE at starter and see if you have 12volt with Key in START.

 

the Low beam lights do not use the key switch so that might be a separate issue also. which might be more fuse or the main wire going to the starter lug to suplly the fuse box. I forgot what you call it(fusable link. IM NOT A 620 expert BUT MAYBE THERE IS 2 WIRES ON A 620 iM NOT SURE.

 

DASH WARNING LIGHTS ?  recheck the ignition key/ fuse on this. I had a bad alternator/ or was it a solid state volt reg would pop) and it would blow fuses.then I would loose my ignition light

 

Edited by banzai510(hainz)

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Still not working. I have been starting it with a trigger starter. Going to try the relay set up. Just haven't had the time. 

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Measure the start voltageon the

On 11/10/2020 at 3:55 PM, datzenmike said:

 

 

 

STARTER

Check that the small Black/Yellow wire to the starter solenoid is secure and tight on the solenoid. If OK pull wire off and check voltage to it when in the START position. If near 12v and no start then the solenoid may be bad. If 4-8V then the start signal is weak.  Use this weak signal to trip a hot start relay....  

 

 

 

If the ignition switch is bad and there is no start signal putting a hot start relay won't do a thing.

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