Bad battery cables - diagnosis
Just helped a good friend with a problem i thought i would share.
His coach was working fine, then the generator would not turn over and start.
He has new coach batteries ( 2 x 6 volt Optima's in series) and when he turned on the interior lights on coach power, then hits the genny, all the lights went dim and only 8 volts at the generator starter solenoid.
First thought, jammed starter on the Onan, and all voltage readings suggested it. Jumped a fresh 12v battery across the two 6v in series, same problem. On shore power the 2 x 6's appear to be charging at 13.7 volts.
After some further testing with a very accurate digital voltmeter, found that lower battery in chain the one going to chassis, had 6.15v, and across the two 12.22v.
BUT, from battery 1 positive to battery 2 negative, a voltage drop of 0.5 volts with no load.
Diagnosis, bad jumper cable from battery 1 + to battery 2 -, bypassed it with a big jumper cable, generator started right away.
Hope this may help others who have 2 x 6 volt batteries in series for their coach supply, and a clue to check the ground cables whenever you have a starting problem.